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