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

colon-equals, database, mysql, operators

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 | 
+------+------+------+--------------------+

Problem

What is the difference in between ``` set test_var = 20; ``` and ``` set test_var:=20; ``` as they both seem to assign the value ?

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