Help Center/ MapReduce Service/ Component Operation Guide (Normal)/ Using CarbonData (for MRS 3.x or Later)/ CarbonData Syntax Reference/ DDL/ CHANGE DATA TYPE
Updated on 2024-12-11 GMT+08:00
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CHANGE DATA TYPE

Function

This command is used to convert INT to BIGINT or increase decimal precision.

Syntax

ALTER TABLE [db_name.]table_name CHANGE col_name col_name changed_column_type;

Parameters

Table 1 CHANGE DATA TYPE parameters

Parameter

Description

db_name

Database name. If this parameter is not specified, the current database is selected.

table_name

Table name.

col_name

Name of a column in a table. A column name consists of letters, digits, and underscores (_).

changed_column_type

Target data type.

Precautions

  • The decimal precision conversion is available only when no data is lost. The decimal precision is represented in the (precision, scale) format.

    Example:

    • Unavailable: Decimal precision cannot be changed from (10,2) to (10,5) because only the scale increases, but the total number of digits remains unchanged.
    • Available: Decimal precision can be changed from (10,2) to (12,3). The total number of digits increases by 2 but the scale increases only by 1, which does not cause any data loss.
  • The maximum precision allowed is (38,38).

Example Value

  • Convert the data type of column a1 from INT to BIGINT.

    ALTER TABLE test_db.carbon CHANGE a1 a1 BIGINT;

  • Change the precision of column a1 from 10 to 18.

    ALTER TABLE test_db.carbon CHANGE a1 a1 DECIMAL(18,2);

Response

You can run the DESCRIBE command to check the changed data type of the modified column.

Parent topic: DDL