Graphical introduction to the difference between := and = in MySQL

The difference between := and =

=

• Only when setting and updating does it have the same effect as :=, that is, assignment; otherwise it has the effect of equality. In view of this, when using variables to implement line numbers, you must use :=

:=

• It not only has the function of assigning values ​​when setting and updating, but also when selecting.

If you understand the difference between = and :=, then you will understand the following phenomenon.

@num:=@num+1, := is the function of assignment, so @num+1 is executed first, and then the value is assigned to @num, so the function of row number can be correctly realized.

@num=@num+1, here = means equal, @num is not equal to @num+1, so it always returns 0. If it is changed to @num=@num, it always returns 1. In the MySQL database, 1 represents true and 0 represents false.

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