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Comment: add links to DDL doc for ALTER TABLE CHANGE COLUMN

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  1. Determine what precision/scale you would like to set for the decimal column in the table.
  2. For each decimal column in the table, update the column definition to the desired precision/scale using the ALTER TABLE command:

    Code Block
    sql
    sql
    ALTER TABLE foo CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);

    If the table is not a partitioned table, then you are done.  If the table has partitions, then go on to step 3.

  3. If the table is a partitioned table, then find the list of partitions for the table:

    Code Block
    sql
    sql
    SHOW PARTITIONS foo;
     
    ds=2008-04-08/hr=11
    ds=2008-04-08/hr=12
    ...
  4. Each existing partition in the table must also have its DECIMAL column changed to add the desired precision/scale.

    This can be done with a single ALTER single ALTER TABLE CHANGE COLUMN by using dynamic partitioning (available for ALTER TABLE CHANGE COLUMN in Hive 0.14 or later, with HIVE-8411):

    Code Block
    sql
    sql
    SET hive.exec.dynamic.partition = true;
     
    -- hive.exec.dynamic.partition needs to be set to true to enable dynamic partitioning with ALTER PARTITION
    -- This will alter all existing partitions of the table - be sure you know what you are doing!
    ALTER TABLE foo PARTITION (ds, hr) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);

     

    Alternatively, this can be done one partition at a time using ALTER TABLE CHANGE COLUMN, by specifying one partition per statement (This is available in Hive 0.14 or later, with HIVE-7971.):

    Code Block
    sql
    sql
    ALTER TABLE foo PARTITION (ds='2008-04-08', hr=11) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);
    ALTER TABLE foo PARTITION (ds='2008-04-08', hr=12) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);
    ...

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