If condition in mysql query

Question

I've searched through google and here but didn't find an answer to my question.

I'm trying to use IF in a query (not stored procedure) in that way:

IF EXISTS (SELECT *  FROM TABLE WHERE COLUMN=VALUE) THEN
DO SOMETHING
END IF;

I've tryed in MySql Workbench and didn't work (Syntax error).

Anybody knows if it's possible to use IF in that way?

Thanks in advance.

What SOMETHING do you wish to DO ?

eggyal
– eggyal

2013-01-19 17:05:27 +00:00
Commented Jan 19, 2013 at 17:05 — eggyal
– eggyal, Commented Jan 19, 2013 at 17:05
SOMETHING in that case in an INSERT .

Valerio
– Valerio

2013-01-19 17:33:38 +00:00
Commented Jan 19, 2013 at 17:33 — Valerio
– Valerio, Commented Jan 19, 2013 at 17:33

Dutow · Accepted Answer · 2013-01-19 17:21:33Z

1

It depends on what is SOMETHING

If it is an UPDATE, DELETE or SELECT, you can specify the conditions in the where clause.

WHERE IF( (SELECT COUNT(*) FROM TABLE WHERE COLUMN=VALUE) > 0, 1, 2) = 1

For other statements (INSERT, CREATE, etc.) i don't think this is possible.

answered Jan 19, 2013 at 17:21

Dutow

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4 Comments

Valerio Over a year ago

I need to do an insert but before that I need to check if already exists a row with these values.

eggyal Over a year ago

@Valerio: So, if a record already exists with COLUMN=VALUE you don't want the INSERT to be performed? Why not define a UNIQUE index over COLUMN, which will enforce such a constraint for you?

Dutow Over a year ago

for inserts, see the INSERT ... ON DUPLICATE KEY UPDATE. It is not exactly the same, but maybe it is what you are looking for

Valerio Over a year ago

@eggyal: In my case I need to check 4 column for duplicate value. I'll try in that way. Thanks a lot.

ypercubeᵀᴹ · Accepted Answer · 2013-01-19 18:22:53Z

0

In your comments you say that "SOMETHING" is an INSERT operation. You can then, instead of:

INSERT INTO tableName
  (colA, colB, ...)
VALUES
  (a, b, ...) ;

use:

INSERT INTO tableName
  (colA, colB, ...)
SELECT
  a, b, ... 
FROM 
  dual
WHERE
  EXISTS (SELECT * FROM TABLE WHERE COLUMN=VALUE) ;

answered Jan 19, 2013 at 18:22

ypercubeᵀᴹ

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3 Comments

Valerio Over a year ago

Didn't know this syntax :( . I'm gonna try. Thanks!

Valerio Over a year ago

OK, I've tryed this syntax and I need to insert only if record doesn't alredy exists so after a couple of test I've seen that the correct syntax for me is : INSERT INTO tableName (colA, colB, ...) SELECT a, b, ... FROM dual WHERE NOT EXISTS (SELECT * FROM TABLE WHERE COLUMN=VALUE);

Valerio Over a year ago

Thanks ! I've some problem with writing comments ;)

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