What's the difference between := and = in MySQL?
mysql
Solution
In short, when using `SET` they both act as assignment operators, but in any non-set statements, `:=` is for assingment and `=` checks for equality.
For SET, either = or := can be used as the assignment operator.
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 = is treated as a 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 |
+------+------+------+--------------------+
Taken from MySQL 8.4 User Defined Variables
Problem
``` mysql> set @num := 1; Query OK, 0 rows affected (0.00 sec) mysql> set @num = 0; Query OK, 0 rows affected (0.00 sec) mysql> select @num; +------+ | @num | +------+ | 0 | +------+ 1 row in set (0.00 sec) ``` Seems both works.