MaxCompute:Type conversions

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) = 1 to 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) = 1 to 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) = 1.0 to convert 1 of the STRING type to 1.0 of the DOUBLE type.
• The default format yyyy-mm-dd hh:mi:ss is 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 DECIMAL operation 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<STRING>.
  • ARRAY<BIGINT> can be explicitly converted to ARRAY<INT>. Implicit conversions are not supported.
  • ARRAY<BIGINT> cannot be implicitly or explicitly converted to ARRAY<DATETIME>.
  • 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.

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 IN are 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/A

  Note

  • 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.
• 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.

• 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.

• 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.