mySQL select which query evaluate by parameter

Question

I've a query like this one:

SELECT IF(@param = 42, 'static', SELECT ... );

But it doesn't work because I can't insert a SELECT statement inside a IF(). My problem is that I can't do otherwise (use an if-then statement outside sql) because to "architecture restrictions".

Any solution to select if evaluate or not a query based to parameter value?

Is the second select static? In that case you can just move the IF inside the query. If ... is foo FROM bar you get SELECT (case when @param = 42 then 'static' else foo end) FROM bar. — Klas Lindbäck
– Klas Lindbäck, Commented Oct 6, 2014 at 12:11

Gordon Linoff · Accepted Answer · 2014-10-06 11:45:23Z

2

You don't need a select:

select (case when @param = 42 then 'static' else date_format(now(), '%Y-%m-%d') end)

Note that you are trying to mix two different types -- a datetime and string. You should explicitly convert the datetime to a string, using your preferred format.

You can write this with if(). case is slightly more general and the ANSI standard.

answered Oct 6, 2014 at 11:45

Gordon Linoff

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2 Comments

Alvins Over a year ago

My fault. I need to run a generic query, not only a now(). It only was for a short example.

Gordon Linoff Over a year ago

@Alvins . . . If you need the subquery, put it in parentheses.

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