DB2 How to use case with multiple conditions? - db2

Question

I have a DB2 Server and I want to select data depending on the condition.
If I have the Value Value in the ColumnX, ColumnY or ColumnZ it should search for it between the TB2.Column1 and TB3.Column1
My statement is a bunch of left outer joins but it looks like that:
SELECT
CASE
WHEN (TB1.ColumnX || TB1.ColumnY || TB1.ColumnZ) = 'Value'
THEN Statement1
ELSE ' '
END AS MyColumn
FROM
TB1 LEFT OUTER JOIN TB2 ON TB1.JOINCOL = TB2.JOINCOL
LEFT OUTER JOIN TB3 ON TB2.JOINCOL2 = TB3.JOINCOL
WHERE TB1.Column1 between TB2.Column1 and TB3.Column1
But it doesn't work, is there a mistake in the syntax?

Answer 1

It is not possible to check for multiple equalities using just a single expression. You may use the following syntax trick:
CASE WHEN 'Value' IN (TB1.ColumnX, TB1.ColumnY, TB1.ColumnZ)
THEN Statement1 ELSE ' ' END AS MyColumn
The alternative to this would be to repeat the full equality check for each column:
SELECT
CASE
WHEN TB1.ColumnX = 'Value' OR
TB1.ColumnY = 'Value' OR
TB1.ColumnZ = 'Value'
THEN Statement1
ELSE ' '
END AS MyColumn
FROM
TB1 LEFT OUTER JOIN TB2
ON TB1.JOINCOL = TB2.JOINCOL
LEFT OUTER JOIN TB3
ON TB2.JOINCOL2 = TB3.JOINCOL
WHERE
TB1.Column1 BETWEEN TB2.Column1 AND TB3.Column1;
If you need to refer to the CASE expression in the WHERE clause, then you have two choices. First, you may subquery your current query, and assign an alias to the CASE expression:
SELECT *
FROM
(
SELECT CASE WHEN ... AS exp
FROM TB1 ...
) t
WHERE exp = ...
Or, you may avoid the subquery and just repeat the entire CASE expression in the WHERE clause.