MySQL declaring variables and assigning values

Variables in SQL Server must be affirmed first and then assigned values:

The local variables are identified with one @ and the global variables with two @ (common global variables are usually defined );

Declare the local variable Syntax: declare @ variable name data type; for example, declare @ num int;

Value assignment: There are two methods (@ num is the variable name and value is the value)

Set @ num = value; or select @ num = value;

If you want to obtain a field value in the query statement, you can use select to assign values to the variable, as shown below:

Select @ num = field name from table name where ......

MySQL variables do not need to be stated beforehand. You can simply use "@ variable name" when using them.

First usage: Set @ num = 1; or set @ num: = 1; // use the variable to save the data. Use the @ num variable directly.

Second usage: Select @ num: = 1; or select @ num: = field name from table name where ......

Note that the above two values can be set with "=" or ": =", but ": =" must be used for select"