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mysqldatabaseoperatorscolon-equals

What is the difference between = and := in MySQL?

What is the difference in between 

set test_var = 20;

and 

set test_var:=20;

as they both seem to assign the value ?

Solution

  • Both of them are assignment operators but one thing I can find their differences is that = can be used to perform boolean operation while := cannot.

    valid: SUM(val = 0)
    Invalid: SUM(val := 0)

    FROM User-Defined Variables

    One more thing, You can also assign a value to a user variable in statements other than SET. In this case, the assignment operator must be := and not = because the latter is treated as the comparison operator = in non-SET statements.

    mysql> SET @t1=1, @t2=2, @t3:=4;
mysql> SELECT @t1, @t2, @t3, @t4 := @t1+@t2+@t3;
+------+------+------+--------------------+
| @t1  | @t2  | @t3  | @t4 := @t1+@t2+@t3 |
+------+------+------+--------------------+
|    1 |    2 |    4 |                  7 | 
+------+------+------+--------------------+