MaxCompute SQL allows you to convert data types. Two conversion methods are supported: explicit conversion and implicit conversion.
Y indicates that the conversion is supported. N indicates that the conversion is not supported. N/A indicates that the conversion is not required. An error is returned if an unsupported explicit conversion is performed.
SELECT CAST(user_id AS DOUBLE) AS new_id; SELECT CAST('2015-10-01 00:00:00' AS DATETIME) AS new_date; SELECT CAST(ARRAY(1,2,3) AS ARRAY<STRING>); SELECT CONCAT_WS(',', CAST(ARRAY(1, 2) AS ARRAY<STRING>));
- If a value of the DOUBLE type is converted into that of the BIGINT type, digits after the decimal point are removed. For example, you can execute
CAST(1.6 AS BIGINT) = 1to convert 1.6 of the DOUBLE Type to 1 of the BIGINT type.
- If a value of the STRING type that meets the format of the DOUBLE type is converted into the BIGINT type, the STRING type is first converted into the DOUBLE type and then to the BIGINT type. During the conversion, the digits after the decimal point are removed. For example, you can execute
CAST("1.6" AS BIGINT) = 1to convert 1.6 of the STRING type to 1 of the BIGINT type.
- If a value of the STRING type that meets the format of the BIGINT type is converted into the DOUBLE type, one digit is retained after the decimal point. For example, you can execute
CAST("1" AS DOUBLE) = 1.0to convert 1 of the STRING type to 1.0 of the DOUBLE type.
- The default format
yyyy-mm-dd hh:mi:ssis used during the conversion that involves the DATETIME type.
- Some data types cannot be explicitly converted, but can be converted by using SQL built-in functions. For example, you can use the TO_CHAR function to convert the BOOLEAN type into the STRING type. For more information, see TO_CHAR. You can also use the TO_DATE function to convert the STRING type into the DATETIME type. For more information, see TO_DATE.
- If the value of the DECIMAL type exceeds its value range, the
CAST STRING TO DECIMALoperation may cause errors, such as overflow of the most significant bit or removal of the least significant bit.
- A conversion from the DECIMAL type to the DOUBLE or FLOAT type results in a loss of precision. In scenarios where high precision is required, for example, when you calculate the bill amount or premium rate, we recommend that you retain the DECIMAL type.
- MaxCompute allows you to convert complex data types. Implicit conversions between complex data types can be implemented only when their subtypes support implicit conversions. Explicit conversions between complex data types can be implemented only when their subtypes support explicit conversions. If you convert the STRUCT type, field names can be inconsistent, but the number of fields must be consistent and these fields must support implicit or explicit conversions. Examples:
ARRAY<BIGINT>can be implicitly or explicitly converted to
ARRAY<BIGINT>can be explicitly converted to
ARRAY<INT>. Implicit conversions are not supported.
ARRAY<BIGINT>cannot be implicitly or explicitly converted to
STRUCT<a:BIGINT,b:INT>can be implicitly converted to
STRUCT<col1:STRING,col2:BIGINT>. Implicit or explicit conversions to
STRUCT<a:STRING>are not supported.
Implicit conversion and its application scope
Y indicates that the conversion is supported. N indicates that the conversion is not supported. N/A indicates that the conversion is not required. An error is returned if an unsupported implicit conversion is performed or if a conversion fails.
- MaxCompute V2.0 introduces the methods to define constants of the DECIMAL and DATETIME types. For example, 100BD indicates value 100 of the DECIMAL type.
2017-11-11 00:00:00indicates a constant of the DATETIME type. Constants can be directly defined in the VALUES clauses and tables.
- If an implicit conversion is used, MaxCompute automatically converts data types based on context. If the types do not match, you can use the CAST function to explicitly convert data types.
- Implicit conversion rules apply to specific scopes. In specific scenarios, only part of the rules take effect.
SELECT user_id+age+'12345', CONCAT(user_name,user_id,age) FROM user;
- Implicit conversions with relational operators
Relational operators include
=, <>, <, ≤, >, ≥, IS NULL, IS NOT NULL, LIKE, RLIKE, and IN. The rules that use
LIKE, RLIKE, and INare different from those that use other relational operators. The rules described in this section do not apply to the three operators.The following table describes the rules of implicit conversions when data of different types is used for relational operations.
From/To BIGINT DOUBLE STRING DATETIME BOOLEAN DECIMAL BIGINT N/A DOUBLE DOUBLE N N DECIMAL DOUBLE DOUBLE N/A DOUBLE N N DECIMAL STRING DOUBLE DOUBLE N/A DATETIME N DECIMAL DATETIME N N DATETIME N/A N N BOOLEAN N N N N N/A N DECIMAL DECIMAL DECIMAL DECIMAL N N N/ANote
- If two values you want to compare do not support implicit conversions, the relational operation cannot be completed and an error is returned.
- For more information about relational operators, see Operators.
- Implicit conversions with special relational operators
Special relational operators are
LIKE, RLIKE, and IN.
- Syntax of LIKE and RLIKE
source LIKE pattern; source RLIKE pattern;Note
- The source and pattern parameters of LIKE and RLIKE must be of the STRING type.
- Other types can neither be involved in the operation nor be implicitly converted into the STRING type.
- Syntax of IN
key IN (value1, value2, ...)Note
- The data types in the value list next to IN must be consistent.
- If the data types of values include BIGINT, DOUBLE, and STRING, convert the values of the BIGINT and STRING types into the DOUBLE type. If the data types of values include DATETIME and STRING, convert the values of the STRING type into the DATETIME type. Conversions between other data types are not allowed.
- Syntax of LIKE and RLIKE
- Implicit conversions with arithmetic operators
Arithmetic operators include:
+, -, *, /, and %. The following rules apply to implicit conversions with these operators.
- Only the values of the STRING, BIGINT, DOUBLE, and DECIMAL types can be used for arithmetic operations.
- Values of the STRING type are implicitly converted into the DOUBLE type before the arithmetic operations.
- If values of the BIGINT and DOUBLE types are used for the arithmetic operations, the value of the BIGINT type is implicitly converted into the DOUBLE type.
- The values of the DATETIME and BOOLEAN types cannot be used for arithmetic operations.
- Implicit conversions with logical operators
Logical operators include
AND, OR, and NOT. The following rules apply to implicit conversions with these operators:
- Only the values of the BOOLEAN type can be used for logical operations.
- Value of other types cannot be used for logical operations or implicitly converted.
Implicit conversions with built-in functions
- If you call a built-in function and the data type of an input parameter is different from that defined in the function, the data type of the input parameter is converted into the function-defined data type.
- The parameters of each built-in function in MaxCompute SQL have different requirements for implicit conversions. For more information, see Built-in functions.
Implicit conversions with CASE WHEN
- If the return values are of the BIGINT and DOUBLE types, all the values are converted into the DOUBLE type.
- If the return values include those of the STRING type, all the values are converted into the STRING type. If a conversion, such as a conversion from BOOLEAN to STRING fails, an error is returned.
- Conversions between other data types are not allowed.
Conversions between the STRING and DATETIME types
MaxCompute supports conversions between the STRING and DATETIME types. The format
yyyy-mm-dd hh:mi:ss is used during the conversions.
|Time unit||String (not case-sensitive)||Valid value|
- If the first digit of the value range of each time unit is 0, 0 cannot be omitted. For example,
2014-1-9 12:12:12is an invalid DATETIME format and it cannot be converted from the STRING type to the DATETIME type. It must be written as
- Only the STRING type that meets the preceding format requirements can be converted into the DATETIME type. For example,
CAST("2013-12-31 02:34:34" AS DATETIME)converts
2013-12-31 02:34:34of the STRING type to the DATETIME type. Similarly, if the DATETIME type is converted into the STRING type, the
yyyy-mm-dd hh:mi:ssformat is automatically used after the conversion.
CAST("2013/12/31 02/34/34" AS DATETIME) CAST("20131231023434" AS DATETIME) CAST("2013-12-31 2:34:34" AS DATETIME)
CAST("2013-02-29 12:12:12" AS DATETIME) -- An error is returned because February 29, 2013 does not exist. CAST("2013-11-31 12:12:12" AS DATETIME) -- An error is returned because November 31, 2013 does not exist.
MaxCompute provides the TO_DATE function to convert the STRING type that does not meet the format of the DATETIME type to the DATETIME type. For more information, see TO_DATE.