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Status Delivered
Workspace Db2 for z/OS
Created by Guest
Created on May 24, 2021

Different Column Names for Union Query

IBM Db2 z/OS development team to allow different column names in different parts of a UNION clause, as long as their types match, and assign the column names from the first part of the UNION clause to the columns of resulting table

Needed by Date May 31, 2021
  • Guest
    Reply
    |
    Jun 15, 2021

    Okay thanks.

  • Admin
    Janet Figone
    Reply
    |
    Jun 15, 2021

    Hello Benjamin, Below please find feedback from development. Thank you.

    Alias can be added as in below. That allows customer to specify column name for the result of UNION.

    SELECT * FROM (

    SELECT C1,C2 FROM T1 UNION

    SELECT C2,C1 FROM T1 UNION

    SELECT C3,C4 FROM T1

    ) AS TX(C1,C2)

  • Guest
    Reply
    |
    Jun 15, 2021

    Hi,
    Thanks, it seems the problem is an alias cannot be used. The column name returned is a number. For example,
    SELECT
    T1.C1 AS C1Alias
    FROM
    T1
    UNION
    SELECT
    T2.C1
    FROM
    T2
    benjamin

  • Guest
    Reply
    |
    Jun 15, 2021

    Hi Janet,


    You are right that the query runs fine, but, Db2 assigns standard column names (Col1, Col2) for such result sets. Benjamin was looking for Db2 to assign the column names as C1 and C2 (as they are the column names for the first part of the query) for your example.

  • Admin
    Janet Figone
    Reply
    |
    Jun 15, 2021

    Hi Benjamin, I'm marking this delivered as it currently supported.

    For example, the following SQL runs successfully on Db2.

    SELECT * FROM (

    SELECT C1,C2 FROM T1 UNION

    SELECT C2,C1 FROM T1 UNION

    SELECT C3,C4 FROM T1

    );

    Please let us know if you have any further questions. Thank you!

  • Guest
    Reply
    |
    May 27, 2021

    It is never required to have the same column name across union legs. It works as long as data type matches.


    For example, the following SQL runs successfully on Db2.


    SELECT * FROM (

    SELECT C1,C2 FROM T1 UNION

    SELECT C2,C1 FROM T1 UNION

    SELECT C3,C4 FROM T1

    );