Aggregate functions group multiple input records to form a single output record. You can use an aggregate function with a GROUP BY
clause of MaxCompute SQL. This topic describes the syntax, parameters, and examples of aggregate functions that are supported by MaxCompute SQL. It guides you through data development by using aggregate functions.
The following table describes the aggregate functions that are supported by MaxCompute SQL.
Function | Description |
Returns a random value from a specific column. | |
Returns an approximate number of distinct input values in a specified column. | |
Returns the column value of the row that corresponds to the maximum value of a specified column. | |
Returns the column value of a row that corresponds to the minimum value of a specific column. | |
Returns the average value of a column. | |
Aggregates input values based on the bitwise AND operation. | |
Aggregates input values based on the bitwise OR operation. | |
Aggregates the specified columns into an array. | |
Aggregates distinct values from a specified column into an array. | |
Returns the number of records that match a specified criteria. | |
Returns the number of records whose expr value is True. | |
Returns a map that contains the number of times each input value appears. | |
Returns a map that is created by using a and b. a is the key in the map. b is the value of the key in the map. | |
Returns a new map that is the union of all input maps. | |
Returns a new map that is the union of all input maps. The output map sums the values of the matching keys in all input maps. | |
Returns the maximum value of a column. | |
Returns the column value of the row that corresponds to the maximum value of a specified column. | |
Returns the median value of a column. | |
Returns the minimum value of a column. | |
Returns the column value of a row that corresponds to the minimum value of a specific column. | |
Returns a map that is created by using a and b. a is the key in the map. b is used to create an array, which is used as the value of the key in the map. | |
Returns an approximate histogram based on a specified column. | |
Returns approximate percentiles. This function applies to scenarios in which a large amount of data is calculated. | |
Returns the population standard deviation of all input values. | |
Returns the sample standard deviation of all the input values. | |
Returns the sum of a column. | |
Concatenates strings with a specified delimiter. |
Precautions
MaxCompute V2.0 provides additional functions. If the functions that you use involve new data types that are supported in the MaxCompute V2.0 data type edition, you must execute the SET statement to enable the MaxCompute V2.0 data type edition. The new data types include TINYINT, SMALLINT, INT, FLOAT, VARCHAR, TIMESTAMP, and BINARY.
Session level: To use the MaxCompute V2.0 data type edition, you must add
set odps.sql.type.system.odps2=true;
before the SQL statement that you want to execute, and commit and execute them together.Project level: The project owner can run the following command to enable the MaxCompute V2.0 data type edition for the project based on the project requirements. The configuration takes effect after 10 to 15 minutes. Run the following command:
setproject odps.sql.type.system.odps2=true;
For more information about
setproject
, see Project operations. For more information about the precautions that you must take when you enable the MaxCompute V2.0 data type edition at the project level, see Data type editions.A worker can contain a maximum of 2 million elements.
If you use an SQL statement that includes multiple aggregate functions and the project resources are insufficient, memory overflow may occur. We recommend that you optimize the SQL statement or purchase computing resources based on your business requirements.
Syntax
Syntax of an aggregate function:
<aggregate_name>(<expression>[,..]) [within group (order by <col1>[,<col2>…])] [filter (where <where_condition>)]
<aggregate_name>(<expression>[,..])
: a built-in aggregate function or a user-defined aggregate function (UDAF). The format of an aggregate function is based on its syntax.within group (order by <col1>[,<col2>…])
: If the syntax of an aggregate function includes this expression, the system automatically sorts the input data of<col1>[,<col2>…]
in ascending order. To sort the input data in descending order, use the expressionwithin group (order by <col1>[,<col2>…] [desc])
.Before you use this expression, take note of the following limits:
You can use this expression only for WM_CONCAT, COLLECT_LIST, COLLECT_SET, and UDAFs.
If multiple aggregate functions of a SELECT statement include the expression
within group (order by <col1>[,<col2>…])
,order by <col1>[,<col2>…]
must be the same for these functions.If the parameters of an aggregate function include the DISTINCT keyword, columns with distinct values must be specified in the expression
order by <col1>[,<col2>…]
. Columns that are specified in theORDER BY
clause are a subset of columns with distinct values. The data type of the fields in the expression<col1>[,<col2>…]
must be the same as the data type of the input parameter of the aggregate function.NoteOnly one input parameter can be specified in an aggregate function that uses the expression
within group (order by <col1>[,<col2>…])
. Therefore, if the input parameter in the aggregate function includes the DISTINCT keyword, only one column can be specified in theORDER BY
clause. The data type of the column must be the same as the data type of the input parameter of the aggregate function.For example, if the input parameter of the WM_CONCAT function is of the STRING data type, the data type of the field specified in the
ORDER BY
clause must also be STRING. For more information, see Example 4. For more information about how to create the emp table, see Sample data.
Examples:
-- Example 1: Sort the input data in ascending order and return the output data. select x, wm_concat(',', y) within group (order by y) from values('k', 1),('k', 3),('k', 2) as t(x, y) group by x; -- The following result is returned: +------------+------------+ | x | _c1 | +------------+------------+ | k | 1,2,3 | +------------+------------+ -- Example 2: Sort the input data in descending order and return the output data. select x, wm_concat(',', y) within group (order by y desc) from values('k', 1),('k', 3),('k', 2) as t(x, y) group by x; -- The following result is returned: +------------+------------+ | x | _c1 | +------------+------------+ | k | 3,2,1 | +------------+------------+ -- Example 3 select id, wm_concat(distinct ',', name) within group (order by name desc) from values('k', '1'),('k', '3'),('k', '2') as t(id, name) group by id; -- The following result is returned: +------------+------------+ | id | _c1 | +------------+------------+ | k | 3,2,1 | +------------+------------+ -- Example 4 -- The parameters of an aggregate function include the DISTINCT keyword. In this case, if the input parameter sal of the WM_CONCAT function is of the BIGINT data type, the data type of the input parameter is implicitly converted into a value of the STRING data type. -- To ensure data type consistency, you must use the CAST function to convert the data type of the input parameter sal into a value of the STRING data type. Otherwise, an error is reported. select deptno, wm_concat(distinct ',', sal) within group (order by cast(sal as STRING ) desc) from emp group by deptno order by deptno; -- The following result is returned: +------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 5000,2450,1300 | | 20 | 800,3000,2975,1100 | | 30 | 950,2850,1600,1500,1250 | +------------+------------+
[filter (where <where_condition>)]
: If an aggregate function includes this expression, the aggregate function processes only the data that meets the condition specified by<where_condition>
. For more information about<where_condition>
, see WHERE clause (where_condition).Before you use this expression, take note of the following limits:
Only built-in aggregate functions support this expression. UDAFs do not support this expression.
count(*)
supports the expression[filter (where <where_condition>)]
.The COUNT_IF function does not support the expression
[filter (where <where_condition>)]
.
Examples:
-- Example 1: Filter and aggregate data. select sum(x), sum(x) filter (where y > 1), sum(x) filter (where y > 2) from values(null, 1),(1, 2),(2, 3),(3, null) as t(x, y); -- The following result is returned: +------------+------------+------------+ | _c0 | _c1 | _c2 | +------------+------------+------------+ | 6 | 3 | 2 | +------------+------------+------------+ -- Example 2: Use multiple aggregate functions to filter and aggregate data. select count_if(x > 2), sum(x) filter (where y > 1), sum(x) filter (where y > 2) from values(null, 1),(1, 2),(2, 3),(3, null) as t(x, y); -- The following result is returned: +------------+------------+------------+ | _c0 | _c1 | _c2 | +------------+------------+------------+ | 1 | 3 | 2 | +------------+------------+------------+
Sample data
This section provides sample source data and examples for you to understand how to use the functions. Create a table named emp and insert the sample data into the table. Sample commands:
create table if not exists emp
(empno bigint,
ename string,
job string,
mgr bigint,
hiredate datetime,
sal bigint,
comm bigint,
deptno bigint);
tunnel upload emp.txt emp;
The emp.txt file contains the following sample data:
7369,SMITH,CLERK,7902,1980-12-17 00:00:00,800,,20
7499,ALLEN,SALESMAN,7698,1981-02-20 00:00:00,1600,300,30
7521,WARD,SALESMAN,7698,1981-02-22 00:00:00,1250,500,30
7566,JONES,MANAGER,7839,1981-04-02 00:00:00,2975,,20
7654,MARTIN,SALESMAN,7698,1981-09-28 00:00:00,1250,1400,30
7698,BLAKE,MANAGER,7839,1981-05-01 00:00:00,2850,,30
7782,CLARK,MANAGER,7839,1981-06-09 00:00:00,2450,,10
7788,SCOTT,ANALYST,7566,1987-04-19 00:00:00,3000,,20
7839,KING,PRESIDENT,,1981-11-17 00:00:00,5000,,10
7844,TURNER,SALESMAN,7698,1981-09-08 00:00:00,1500,0,30
7876,ADAMS,CLERK,7788,1987-05-23 00:00:00,1100,,20
7900,JAMES,CLERK,7698,1981-12-03 00:00:00,950,,30
7902,FORD,ANALYST,7566,1981-12-03 00:00:00,3000,,20
7934,MILLER,CLERK,7782,1982-01-23 00:00:00,1300,,10
7948,JACCKA,CLERK,7782,1981-04-12 00:00:00,5000,,10
7956,WELAN,CLERK,7649,1982-07-20 00:00:00,2450,,10
7956,TEBAGE,CLERK,7748,1982-12-30 00:00:00,1300,,10
Filter expressions
Limits
Only built-in aggregate functions of MaxCompute support filter expressions. UDAFs do not support filter expressions.
COUNT(*)
cannot be used with filter expressions. Use the COUNT_IF function with filter expressions.
Syntax
<aggregate_name>(<expression>[,...]) [filter (where <where_condition>)]
Description
All aggregate functions support filter expressions. If you specify a filter condition, only the row data that meets the filter condition can be passed to the related aggregate function for data processing.
Parameters
aggregate_name: required. The name of the aggregate function. Select an aggregate function that is described in this topic based on your business requirements.
expression: required. The parameters of the aggregate function that you select. Specify this parameter based on the description of the aggregate function that you select.
where_condition: optional. The filter condition. For more information about where_condition, see WHERE clause (where_condition).
Return value
For more information, see the description of the return value for each aggregate function.
Sample statement:
select sum(sal) filter (where deptno=10), sum(sal) filter (where deptno=20), sum(sal) filter (where deptno=30) from emp;
The following result is returned:
+------------+------------+------------+ | _c0 | _c1 | _c2 | +------------+------------+------------+ | 17500 | 10875 | 9400 | +------------+------------+------------+
ANY_VALUE
Syntax
any_value(<colname>)
Description
Returns a random value from a specific column. This function is an additional function of MaxCompute V2.0.
Parameters
colname: required. The name of a column, which can be of any data type.
Return value
The data type of the return value is the same as the data type of the colname parameter. If the value of the colname parameter is null, the row that contains this value is not used for calculation.
Examples
Example 1: Select one of the employees. Sample statement:
select any_value(ename) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | SMITH | +------------+
Example 2: Use this function with
GROUP BY
to group all employees based on the deptno column and select one employee from each group. Sample statement:select deptno, any_value(ename) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | CLARK | | 20 | SMITH | | 30 | ALLEN | +------------+------------+
APPROX_DISTINCT
Syntax
approx_distinct(<colname>)
Description
Returns the approximate number of distinct input values in a specified column. This function is an additional function of MaxCompute V2.0.
Parameters
colname: required. The name of the column from which duplicates need to be removed.
Return value
A value of the BIGINT type is returned. This function produces a standard error of 5%. If a value of the column that is specified by the colname parameter is null, the row that contains this value is not used for calculation.
Examples
Example 1: Calculate an approximate number of distinct values in the sal column. Sample statement:
select approx_distinct(sal) from emp;
The following result is returned:
+-------------------+ | numdistinctvalues | +-------------------+ | 12 | +-------------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the approximate number of distinct values in the sal column. Sample statement:select deptno, approx_distinct(sal) from emp group by deptno;
The following result is returned:
+------------+-------------------+ | deptno | numdistinctvalues | +------------+-------------------+ | 10 | 3 | | 20 | 4 | | 30 | 5 | +------------+-------------------+
ARG_MAX
Syntax
arg_max(<valueToMaximize>, <valueToReturn>)
Description
Finds the row in which the value of valueToMaximize is included and returns the value of valueToReturn in the row. This function is an additional function of MaxCompute V2.0.
Parameters
valueToMaximize: required. The name of a column, which can be of any data type.
valueToReturn: required. The name of a column, which can be of any data type.
Return value
The data type of the return value is the same as the data type of the valueToReturn parameter. If multiple rows contain the largest value of valueToMaximize, the value of valueToReturn in one of the rows is randomly returned. If the value of valueToMaximize is null, the row that contains this value is not used for calculation.
Examples
Example 1: Return the name of the employee who has the highest salary. Sample statement:
select arg_max(sal, ename) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | KING | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and return the name of the employee with the highest salary in each group. Sample statement:select deptno, arg_max(sal, ename) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | KING | | 20 | SCOTT | | 30 | BLAKE | +------------+------------+
ARG_MIN
Syntax
arg_min(<valueToMinimize>, <valueToReturn>)
Description
Finds the row in which the minimum value of valueToMinimize is included and returns the value of valueToReturn in the row. This function is an additional function of MaxCompute V2.0.
Parameters
valueToMinimize: required. A value of any data type.
valueToReturn: required. A value of any data type.
Return value
The data type of the return value is the same as the data type of the valueToReturn parameter. If multiple rows contain the smallest value of valueToMinimize, the value of valueToReturn in one of the rows is randomly returned. If the value of valueToMinimize is null, the row that contains this value is not used for calculation.
Examples
Example 1: Return the name of the employee who has the lowest salary. Sample statement:
select arg_min(sal, ename) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | SMITH | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and return the name of the employee with the lowest salary in each group. Sample statement:select deptno, arg_min(sal, ename) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | MILLER | | 20 | SMITH | | 30 | JAMES | +------------+------------+
AVG
Syntax
DECIMAL|DOUBLE avg(<colname>)
Description
Returns the average value of a column.
Parameters
colname: required. Column values support all data types and can be converted into the DOUBLE type before calculation.
Return value
If the value of colname is null, the row that contains this value is not used for calculation. The following table describes the mappings between data types of input data and return values.
Input type
Return value type
TINYINT
DOUBLE
SMALLINT
DOUBLE
INT
DOUBLE
BIGINT
DOUBLE
FLOAT
DOUBLE
DOUBLE
DOUBLE
DECIMAL
DECIMAL
Examples
Example 1: Calculate the average salary (sal) values of all employees. Sample statement:
select avg(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 2222.0588235294117 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the average salary (sal) values of employees in each department. Sample statement:select deptno, avg(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 2916.6666666666665 | | 20 | 2175.0 | | 30 | 1566.6666666666667 | +------------+------------+
BITWISE_AND_AGG
Syntax
bigint bitwise_and_agg(bigint value)
Description
Aggregates input values based on the bitwise AND operation.
Parameters
value: required. A value of the BIGINT type. The null value is not used for calculation.
Return value
A value of the BIGINT type is returned.
Examples
select id, bitwise_and_agg(v) from values (1L, 2L), (1L, 1L), (2L, null), (1L, null) t(id, v) group by id;
The following result is returned:
+------------+------------+ | id | _c1 | +------------+------------+ | 1 | 0 | | 2 | NULL | +------------+------------+
BITWISE_OR_AGG
Syntax
bigint bitwise_or_agg(bigint value)
Description
Aggregates input values based on the bitwise OR operation.
Parameters
value: required. A value of the BIGINT type. The null value is not used for calculation.
Return value
A value of the BIGINT type is returned.
Examples
select id, bitwise_or_agg(v) from values (1L, 2L), (1L, 1L), (2L, null), (1L, null) t(id, v) group by id;
The following result is returned:
+------------+------------+ | id | _c1 | +------------+------------+ | 1 | 3 | | 2 | NULL | +------------+------------+
COLLECT_LIST
Syntax
array collect_list(<colname>)
Description
Aggregates the values that are specified by colname into an array. This function is an additional function of MaxCompute V2.0.
Parameters
colname: required. The name of a column, which can be of any data type.
Return value
A value of the ARRAY type is returned. If a value of the column specified by colname is null, the row that contains this value is not used for calculation.
Examples
Example 1: Aggregate the salary (sal) values of all employees into an array. Sample statement:
select collect_list(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | [800,1600,1250,2975,1250,2850,2450,3000,5000,1500,1100,950,3000,1300,5000,2450,1300] | +------------+
Example 2: Use this function with
GROUP BY
to group all employees based on the deptno column and aggregate the values in the sal column of each group into an array. Sample statement:select deptno, collect_list(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | [2450,5000,1300,5000,2450,1300] | | 20 | [800,2975,3000,1100,3000] | | 30 | [1600,1250,1250,2850,1500,950] | +------------+------------+
Example 3: Use this function with
GROUP BY
to group all employees based on the deptno column and aggregate the values in the sal column of each group after duplicates are removed. Sample statement:select deptno, collect_list(distinct sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | [1300,2450,5000] | | 20 | [800,1100,2975,3000] | | 30 | [950,1250,1500,1600,2850] | +------------+------------+
COLLECT_SET
Syntax
array collect_set(<colname>)
Description
Aggregates the values that are specified by colname into an array with only distinct values. This function is an additional function of MaxCompute V2.0.
Parameters
colname: required. The name of a column, which can be of any data type.
Return value
A value of the ARRAY type is returned. If a value of the column specified by colname is null, the row that contains this value is not used for calculation.
Examples
Example 1: Aggregate the salary (sal) values of all employees into an array with only distinct values. Sample statement:
select collect_set(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | [800,950,1100,1250,1300,1500,1600,2450,2850,2975,3000,5000] | +------------+
Example 2: Use this function with
GROUP BY
to group all employees based on the deptno column and aggregate the values in the sal column of the employees in each group into an array with only distinct values. Sample statement:select deptno, collect_set(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | [1300,2450,5000] | | 20 | [800,1100,2975,3000] | | 30 | [950,1250,1500,1600,2850] | +------------+------------+
COUNT
Syntax
bigint count([distinct|all] <colname>)
Description
Returns the number of records that match a specified criteria.
Parameters
distinct|all: optional. This parameter specifies whether to remove duplicates during the counting. The default value is all, which indicates that all records are counted. If this parameter is set to distinct, only records with distinct values are counted.
colname: required. The name of a column, which can be of any data type. The value of colname can be an asterisk (
*
).count(*)
indicates that the number of all rows is returned.
Return value
A value of the BIGINT type is returned. If a value of the column specified by colname is null, the row that contains this value is not used for calculation.
Examples
Example 1: Calculate the total number of employees in all departments. Sample statement:
select count(*) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 17 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the number of employees in each department. Sample statement:select deptno, count(*) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 6 | | 20 | 5 | | 30 | 6 | +------------+------------+
Example 3: Remove duplicates when you calculate the number of departments. Sample statement:
select count(distinct deptno) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 3 | +------------+
COUNT_IF
Syntax
bigint count_if(boolean <expr>)
Description
Returns the number of records whose expr value is True.
Parameters
expr: required. A BOOLEAN expression.
Return value
A value of the BIGINT type is returned. If the value of the expr parameter is False or the value of a specific column in expr is null, the row that contains this value is not used for calculation.
Examples
select count_if(sal > 1000), count_if(sal <=1000) from emp;
The following result is returned:
+------------+------------+ | _c0 | _c1 | +------------+------------+ | 15 | 2 | +------------+------------+
HISTOGRAM
Syntax
map<K, bigint> histogram(K input);
Description
Returns a map that contains the number of times each input value appears. The keys in the map are the input values. Each value in the map is the number of times an input value appears. The null value is ignored.
Parameters
input: input values, which are used as the keys in the map.
Return value
A map that contains the number of times each input value appears is returned.
Examples
select histogram(a) from values ('hi'), (null), ('apple'), ('pie'), ('apple') t(a);
The following result is returned:
+----------------------------+ | _c0 | +----------------------------+ | {"pie":1,"hi":1,"apple":2} | +----------------------------+
MAP_AGG
Syntax
map<K, V> map_agg(K a, V b);
Description
Returns a map that is created by using a and b. a is the key in the map. b is the value of the key in the map. If the key in the map is null, the key is ignored. If the key field has duplicate values, one of the values is randomly retained.
Parameters
a: an input field that is used as the key in the map.
b: an input field that is used as the value in the map.
Return value
A new map is returned.
Examples
select map_agg(a, b) from values (1L, 'apple'), (2L, 'hi'), (null, 'good'), (1L, 'pie') t(a, b);
The following result is returned:
+------------------------+ | _c0 | +------------------------+ | {"2":"hi","1":"apple"} | +------------------------+
MAP_UNION
Syntax
map<K, V> map_union(map<K, V> input);
Description
Returns a new map that is the union of all input maps. If a key exists in multiple input maps, one of the values that correspond to the key is randomly retained.
Parameters
input: the input maps.
Return value
A new map is returned.
Examples
select map_union(a) from values (map(1L, 'hi', 2L, 'apple', 3L, 'pie')), (map(1L, 'good', 4L, 'this')), (null) t(a);
The following result is returned:
+-----------------------------------------------+ | _c0 | +-----------------------------------------------+ | {"4":"this","1":"good","2":"apple","3":"pie"} | +-----------------------------------------------+
MAP_UNION_SUM
Syntax
map<K, V> map_union_sum(map<K, V> input);
Description
Returns a new map that is the union of all input maps. The output map sums the values of the matching keys in all input maps. If the value that corresponds to a key is NULL, the value is converted into 0.
NoteThe values in input maps must be of the BIGINT, INT, SMALLINT, TINYINT, FLOAT, DOUBLE, or DECIMAL data type.
Parameters
input: the input maps.
Return value
A new map is returned.
NoteThe values in the new map are of the BIGINT, DOUBLE, or DECIMAL type.
Examples
select map_union_sum(a) from values (map('hi', 2L, 'apple', 3L, 'pie', 1L)), (map('apple', null, 'hi', 4L)), (null) t(a);
The following result is returned:
+----------------------------+ | _c0 | +----------------------------+ | {"apple":3,"hi":6,"pie":1} | +----------------------------+
MAX
Syntax
max(<colname>)
Description
Returns the maximum value of a column.
Parameters
colname: required. The name of a column, which can be of any data type other than BOOLEAN.
Return value
The type of the return value is the same as the type of the colname parameter. The return value varies based on the following rules:
If the value of colname is null, the row that contains this value is not used for calculation.
If the value of colname is of the BOOLEAN type, the value is not used for calculation.
Examples
Example 1: Calculate the highest salary (sal) of all employees. Sample statement:
select max(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 5000 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the highest salary of employees in each department. Sample statement:select deptno, max(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 5000 | | 20 | 3000 | | 30 | 2850 | +------------+------------+
MAX_BY
Syntax
max_by(<valueToReturn>,<valueToMaximize>)
Description
NoteThe MAX_BY function provides the same feature as the ARG_MAX function. The difference lies in the parameter order. The MAX_BY function is introduced in MaxCompute to maintain compatibility with the open source syntax.
Finds the row in which the value of valueToMaximize is included and returns the value of valueToReturn in the row. This function is an additional function of MaxCompute V2.0.
Parameters
valueToMaximize: required. A value of any data type.
valueToReturn: required. A value of any data type.
Return value
The data type of the return value is the same as the data type of the valueToReturn parameter. If multiple rows have the largest value of valueToMaximize, the value of valueToReturn in one of the rows is randomly returned. If the value of valueToMaximize is null, the row that contains this value is not used for calculation.
Examples
Example 1: Return the name of the employee who has the highest salary. Sample statement:
select max_by(ename,sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | KING | +------------+
Example 2: Use this function with
GROUP BY
to group all employees based on the deptno column and return the name of the employee with the highest salary in each group. Sample statement:select deptno, max_by(ename,sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | KING | | 20 | SCOTT | | 30 | BLAKE | +------------+------------+
MEDIAN
Syntax
double median(double <colname>) decimal median(decimal <colname>)
Description
Returns the median value of a column.
Parameters
colname: required. The name of a column, which can be of the DOUBLE or DECIMAL type. If the input value is of the STRING or BIGINT type, it is implicitly converted into the DOUBLE type before calculation.
Return value
If the value of colname is null, the row that contains this value is not used for calculation. The following table describes the mappings between data types of input data and return values.
Input type
Return value type
TINYINT
DOUBLE
SMALLINT
DOUBLE
INT
DOUBLE
BIGINT
DOUBLE
FLOAT
DOUBLE
DOUBLE
DOUBLE
DECIMAL
DECIMAL
Examples
Example 1: Calculate the median salary (sal) values of all employees. Sample statement:
select median(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 1600.0 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the median salary values of employees in each department. Sample statement:select deptno, median(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 2450.0 | | 20 | 2975.0 | | 30 | 1375.0 | +------------+------------+
MIN
Syntax
min(<colname>)
Description
Returns the minimum value of a column.
Parameters
colname: required. The name of a column, which can be of any data type other than BOOLEAN.
Return value
The type of the return value is the same as the type of the colname parameter. The return value varies based on the following rules:
If the value of colname is null, the row that contains this value is not used for calculation.
If the value of colname is of the BOOLEAN type, the value is not used for calculation.
Examples
Example 1: Calculate the lowest salary (sal) of all employees. Sample statement:
select min(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 800 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the lowest salary of employees in each department. Sample statement:select deptno, min(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 1300 | | 20 | 800 | | 30 | 950 | +------------+------------+
MIN_BY
Syntax
min_by(<valueToReturn>,<valueToMinimize>)
Description
NoteThe MIN_BY function provides the same feature as the ARG_MIN function. However, the functions differ in the parameter order. The MIN_BY function is introduced in MaxCompute to maintain compatibility with the open source syntax.
Finds the row in which the minimum value of valueToMinimize is included and returns the value of valueToReturn in the row. This function is an additional function of MaxCompute V2.0.
Parameters
valueToMinimize: required. A value of any data type.
valueToReturn: required. A value of any data type.
Return value
The data type of the return value is the same as the data type of the valueToReturn parameter. If multiple rows contain the smallest value of valueToMinimize, the value of valueToReturn in one of the rows is randomly returned. If the value of valueToMinimize is null, the row that contains this value is not used for calculation.
Examples
Example 1: Return the name of the employee who has the lowest salary. Sample statement:
select min_by(ename,sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | SMITH | +------------+
Example 2: Use this function with
GROUP BY
to group all employees based on the deptno column and return the name of the employee with the lowest salary in each group. Sample statement:select deptno, min_by(ename,sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | MILLER | | 20 | SMITH | | 30 | JAMES | +------------+------------+
MULTIMAP_AGG
Syntax
map<K, array<V>> multimap_agg(K a, V b);
Description
Returns a map that is created by using a and b. a is the key in the map. b is used to create an array, which is used as the value of the key in the map. If the key in the map is null, the key is ignored.
Parameters
a: an input field that is used as the key in the map.
b: an input field that is used as the value in the map. Fields that correspond to the same key are placed in the same array and are used as values in the map.
Return value
A new map is returned.
Examples
select multimap_agg(a, b) from values (1L, 'apple'), (2L, 'hi'), (null, 'good'), (1L, 'pie') t(a, b);
The following result is returned:
+----------------------------------+ | _c0 | +----------------------------------+ | {"2":["hi"],"1":["apple","pie"]} | +----------------------------------+
NUMERIC_HISTOGRAM
Syntax
map<double key, double value> numeric_histogram(bigint <buckets>, double <colname> [, double <weight>])
Description
Returns an approximate histogram based on a specified column. This function is an additional function of MaxCompute V2.0.
Parameters
buckets: required. A value of the BIGINT type. This parameter specifies the maximum number of buckets in the column whose approximate histogram is returned.
colname: required. A value of the DOUBLE type. This parameter specifies the columns whose approximate histograms need to be calculated.
weight: optional. The weight value of data in each row. The value is of the DOUBLE type.
Return value
A value of the
map<double key, double value>
type is returned. In the return value, key indicates the X-axis of the approximate histogram, and value indicates the approximate height of the Y-axis of the approximate histogram. The return value varies based on the following rules:If the value of buckets is null, null is returned.
If the value of colname is null, the row that contains this value is not used for calculation.
Examples
Return an approximate histogram of the sal column. Sample statement:
select numeric_histogram(5, sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | {"1328.5714285714287":7.0,"2450.0":2.0,"5000.0":2.0,"875.0":2.0,"2956.25":4.0} | +------------+
Return the approximate histogram of the sal column. The
deptno
in each row of data indicates the department weight. Sample statement:select numeric_histogram(5, sal, deptno) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | {"2944.4444444444443":90.0,"2450.0":20.0,"5000.0":20.0,"890.0":50.0,"1350.0":160.0} | +------------+
PERCENTILE_APPROX
Syntax
double percentile_approx (double <colname>[, double <weight>], <p> [, <B>])) -- Returns multiple approximate percentiles as an array. array<double> percentile_approx (double <colname> [, double <weight>], array(<p1> [, <p2>...]) [, <B>])
Description
Returns approximate percentiles. This function applies to scenarios in which a large amount of data is calculated. This function sorts the values in a specified column in ascending order and then returns the approximate percentile of the column at the p th percentage. The value of
percentile_approx
starts from 1. For example, a column contains values of 100, 200, and 300, and the sequence numbers of these values are 1, 2, and 3. If you calculate the 0.6th percentile of this column, thePERCENTILE_APPROX
function returns 180, which is calculated by using the following formula:100 + (200 - 100) × 0.8
. This value corresponds to 1.8, which is calculated by using the formula 3 × 0.6 and is between sequence numbers 1 and 2. This function is an additional function of MaxCompute V2.0.NoteDifferences between
PERCENTILE_APPROX
andPERCENTILE
:PERCENTILE_APPROX
is used to calculate an approximate percentile, andPERCENTILE
is used to calculate an exact percentile. If the amount of data is large,PERCENTILE
may fail to run due to memory limits, butPERCENTILE_APPROX
does not have this issue.The implementation of
PERCENTILE_APPROX
is consistent with that ofPERCENTILE_APPROX
in Hive, but the calculation algorithm of PERCENTILE_APPROX is different from that ofpercentile
. If the amount of data is small, the execution result of PERCENTILE_APPROX is different from that ofPERCENTILE
.
Parameters
colname: required. The name of a column, which can be of the DOUBLE type.
weight: optional. The weight value of data in each row. The value is of the DOUBLE type.
p: required. The approximate percentile. Valid values:
[0.0,1.0]
.B: the accuracy of the return value. A higher accuracy indicates a more accurate value. If you do not specify this parameter, 10000 is used.
Return value
A value of the DOUBLE or ARRAY type is returned. The return value varies based on the following rules:
If the value of colname is null, the row that contains this value is not used for calculation.
If the value of p or B is null, an error is returned.
Examples
Example 1: Calculate the 0.3rd percentile in the sal column. Sample statement:
select percentile_approx(sal, 0.3) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 1252.5 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees based on the deptno column and calculate the 0.3rd percentile of employees in each group in the sal column. Sample statement:select deptno, percentile_approx(sal, 0.3) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 1300.0 | | 20 | 950.0 | | 30 | 1070.0 | +------------+------------+
Example 3: Use this function with
GROUP BY
to group all employees based on the deptno column and calculate the 0.3rd, 0.5th, and 0.8th percentiles of employees in each group in the sal column. Sample statement:set odps.sql.type.system.odps2=true; select deptno, percentile_approx(sal, array(0.3, 0.5, 0.8), 1000) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | [1300.0,1875.0,3470.000000000001] | | 20 | [950.0,2037.5,2987.5] | | 30 | [1070.0,1250.0,1580.0] | +------------+------------+
Example 4 (example with weight specified): Use this function with
GROUP BY
to group all employees based on the deptno column and calculate the 0.3rd, 0.5th, and 0.8th percentile of employees in each group in the sal column. Values in thecnt
column of theemp
table indicate the number of employees whose salaries are in the specified percentile. Sample statement:select deptno, percentile_approx(sal, deptno, array(0.3, 0.5, 0.8), 1000) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | [1300.0,1875.0,3470.0] | | 20 | [950.0,2037.5,2987.5] | | 30 | [1070.0,1250.0,1580.0] | +------------+------------+
STDDEV
Syntax
double stddev(double <colname>) decimal stddev(decimal <colname>)
Description
Returns the population standard deviation of all input values.
Parameters
colname: required. The name of a column, which can be of the DOUBLE or DECIMAL type. If the input value is of the STRING or BIGINT type, it is implicitly converted into the DOUBLE type before calculation.
Return value
If the value of colname is null, the row that contains this value is not used for calculation. The following table describes the mappings between data types of input data and return values.
Input type
Return value type
TINYINT
DOUBLE
SMALLINT
DOUBLE
INT
DOUBLE
BIGINT
DOUBLE
FLOAT
DOUBLE
DOUBLE
DOUBLE
DECIMAL
DECIMAL
Examples
Example 1: Calculate the population standard deviation of salary (sal) values of all employees. Sample statement:
select stddev(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 1262.7549932628976 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the population standard deviation of salary values (sal) of employees in each department. Sample statement:select deptno, stddev(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 1546.1421524412158 | | 20 | 1004.7387720198718 | | 30 | 610.1001739241043 | +------------+------------+
STDDEV_SAMP
Syntax
double stddev_samp(double <colname>) decimal stddev_samp(decimal <colname>)
Description
Returns the sample standard deviation of all the input values.
Parameters
colname: required. The name of a column, which can be of the DOUBLE or DECIMAL type. If the input value is of the STRING or BIGINT type, it is implicitly converted into the DOUBLE type before calculation.
Return value
If the value of colname is null, the row that contains this value is not used for calculation. The following table describes the mappings between data types of input data and return values.
Input type
Return value type
TINYINT
DOUBLE
SMALLINT
DOUBLE
INT
DOUBLE
BIGINT
DOUBLE
FLOAT
DOUBLE
DOUBLE
DOUBLE
DECIMAL
DECIMAL
Examples
Example 1: Calculate the sample standard deviation of salary (sal) values of all employees. Sample statement:
select stddev_samp(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 1301.6180541247609 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the sample standard deviation of salary values of employees in each department. Sample statement:select deptno, stddev_samp(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 1693.7138680032901 | | 20 | 1123.3320969330487 | | 30 | 668.3312551921141 | +------------+------------+
SUM
Syntax
DECIMAL|DOUBLE|BIGINT sum(<colname>)
Description
Returns the sum of a column.
Parameters
colname: required. Column values support all data types and can be converted into the DOUBLE type before calculation. The name of a column, which can be of the DOUBLE, DECIMAL, or BIGINT type. If the input value is of the STRING type, it is implicitly converted into the DOUBLE type before calculation.
Return value
If the value of colname is null, the row that contains this value is not used for calculation. The following table describes the mappings between data types of input data and return values.
Input type
Return value type
TINYINT
BIGINT
SMALLINT
BIGINT
INT
BIGINT
BIGINT
BIGINT
FLOAT
DOUBLE
DOUBLE
DOUBLE
DECIMAL
DECIMAL
Examples
Example 1: Calculate the sum of salary (sal) values of all employees. Sample statement:
select sum(sal) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | 37775 | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and calculate the sum of salary values of employees in each department. Sample statement:select deptno, sum(sal) from emp group by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 17500 | | 20 | 10875 | | 30 | 9400 | +------------+------------+
WM_CONCAT
Syntax
string wm_concat(string <separator>, string <colname>)
Description
Concatenates values in colname by using a delimiter that is specified by separator.
Parameters
separator: required. The delimiter, which is a constant of the STRING type.
colname: required. A value of the STRING type. If the input value is of the BIGINT, DOUBLE, or DATETIME type, the value is implicitly converted into the STRING type before calculation.
Return value (The
GROUP BY
clause is specified, and the ORDER BY clause is not specified.)A value of the STRING type is returned. The return value varies based on the following rules:
If the value of separator is not a constant of the STRING type, an error is returned.
If the value of colname is not of the STRING, BIGINT, DOUBLE, or DATETIME type, an error is returned.
If the value of colname is null, the row that contains this value is not used for calculation.
NoteIf the value of
table_name
in theselect wm_concat(',', name) from table_name;
statement is an empty set, null is returned.Examples
Example 1: Concatenate the names (ename) of all employees. Sample statement:
select wm_concat(',', ename) from emp;
The following result is returned:
+------------+ | _c0 | +------------+ | SMITH,ALLEN,WARD,JONES,MARTIN,BLAKE,CLARK,SCOTT,KING,TURNER,ADAMS,JAMES,FORD,MILLER,JACCKA,WELAN,TEBAGE | +------------+
Example 2: Use this function with
GROUP BY
to group all employees by department (deptno) and concatenate the names (ename) of employees in each department. Sample statement:select deptno, wm_concat(',', ename) from emp group by deptno order by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | CLARK,KING,MILLER,JACCKA,WELAN,TEBAGE | | 20 | SMITH,JONES,SCOTT,ADAMS,FORD | | 30 | ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES | +------------+------------+
Example 3: Use this function with
GROUP BY
to group all employees by department (deptno) and concatenate the salary values of the employees in each department after duplicates are removed. Sample statement:select deptno, wm_concat(distinct ',', sal) from emp group by deptno order by deptno;
The following result is returned:
+------------+------------+ | deptno | _c1 | +------------+------------+ | 10 | 1300,2450,5000 | | 20 | 1100,2975,3000,800 | | 30 | 1250,1500,1600,2850,950 | +------------+------------+
Example 4: Use this function with
GROUP BY
andORDER BY
to group all employees by department (deptno), concatenate the salary values (sal) of all employees in each department, and sort the salary values (sal) in a specified order. Sample statement:select deptno, wm_concat(',',sal) within group(order by sal) from emp group by deptno order by deptno;
The following result is returned:
+------------+------------+ |deptno|_c1| +------------+------------+ |10|1300,1300,2450,2450,5000,5000| |20|800,1100,2975,3000,3000| |30|950,1250,1250,1500,1600,2850| +------------+------------+