Mysql - order of the "OR" operator

Question

In a large query, I have

INNER JOIN file
ON ( file.file_id = temp_student_table.converted_file 
     OR file.file_id = temp_student_table.uploaded_file)

If file.file_id = temp_student_table.converted_file is a match, does MySQL check for the second statement? what happens if both of them return a match? Does it only consider the first statement?

No. If it is `OR` and the first matches, the second does not have to be matched. — fedorqui, Oct 30 '14 at 15:47
@fedorqui So if theyre both matched, it only considers the first one. Right? — Nu Gnoj Mik, Oct 30 '14 at 15:48
Why not test it and find out? I can't take more than a minute. — jpw, Oct 30 '14 at 15:48
@Strawberry It matters if one of them has side effects or errors, such as divide by zero. — Barmar, Oct 30 '14 at 15:51
Depends if its a @Strawberry tree. They usually make a lot of noise.. — Nu Gnoj Mik, Oct 30 '14 at 15:52
possible duplicate of [Is the SQL WHERE clause short-circuit evaluated?](http://stackoverflow.com/questions/789231/is-the-sql-where-clause-short-circuit-evaluated) — sp00m, Oct 30 '14 at 15:54
Related: [Short-circuit logic evaluation operators](http://stackoverflow.com/q/16969780/2359271) — Air, Oct 30 '14 at 15:55
The order that MySQL checks the OR function is irrelevant. The OR operator returns true if either or both conditions are true. — Mr. Mascaro, Oct 30 '14 at 15:56

score 0 · Answer 1 · answered Oct 30 '14 at 15:48

0

Since you are using an OR operator here it checks for the first condition.If the first statement is matched then it proceeds.The second one need not be matched in the condtion

answered Oct 30 '14 at 15:48

Avinash Babu

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score 0 · Accepted Answer · answered Oct 30 '14 at 15:51

In an OR condition, it will just evaluate the first condition and exit if it is already true.

OR operator has this behaviour:

A | B | A OR B
0   0     0
0   1     1            0 = False
1   0     1            1 = True
1   1     1

This means the A OR B is true unless A and B are false. For this, A OR B will evaluate the minimum necessary: if A is already true, there is no point in continuing to evaluate the condition.

score 0 · Answer 3 · answered Oct 30 '14 at 15:53

0

In Mysql, OR will return true:

if the first operand is true, in that case the second operand won't be tested
if the first operand is false and the second one is true

answered Oct 30 '14 at 15:53

fluminis

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Mysql - order of the "OR" operator

3 Answers3