Mysql select query condition

Question

I have two database columns in a mysql database, A and B. In a select query, I want to implement this logic:

Select the rows where A is 'X'. If A is not set in a row, then check and select the row only if column B='Y'.

So one can say that column B is a fallback for column A.

How could I construct a SELECT query with 'X' and 'Y' as inputs for the WHERE clause?

Yamikuronue · Accepted Answer · 2011-04-21 17:19:49Z

7

Use boolean logic:

SELECT *
FROM table
WHERE A = 'X' OR (A IS NULL AND B = 'Y')

answered Apr 21, 2011 at 17:19

Yamikuronue

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2 Comments

frabala Over a year ago

I have a question on this solution. This query will return both A and B (because of 'SELECT *') and maybe one of them will be null. Is there a way NOT to return A in case it is null?

Yamikuronue Over a year ago

@frabala If you have a question you should ask using the "Ask Question" link up at the top, it'll get you a lot more responses than a comment on an old answer from last year :)

Marco · Accepted Answer · 2011-04-21 17:19:13Z

2

I think this should work:

SELECT * FROM table
WHERE (A='X') OR ((A IS NULL) AND (B='Y'))

answered Apr 21, 2011 at 17:19

Marco

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Comments

odrm · Accepted Answer · 2011-04-21 17:20:54Z

2

SELECT * FROM table WHERE A='X' OR (A IS NULL AND B='Y')

answered Apr 21, 2011 at 17:20

odrm

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