MySQL 中 = 和 := 的区别 [英] Difference between = and := in MySQL

问题描述

在MySQL中这两个命令有什么区别?

in MySQL what is the difference between these two command?

它们工作得很好，结果总是一样的:

They work perfectly and the result is always the same:

set @numRecords = (select count(*) from config);

set @numRecords := (select count(*) from config);

谢谢大卫

推荐答案

引用 MySQL 5.7 参考手册，第 10.4 节用户定义的变量:

Quoting the MySQL 5.7 Reference Manual, section 10.4 User-Defined Variables:

对于 SET，可以使用 = 或 := 作为赋值运算符.

For SET, either = or := can be used as the assignment operator.

您还可以在其他语句中为用户变量赋值比SET.在这种情况下，赋值运算符必须是 := 而不是 =因为后者在非 SET 中被视为比较运算符 =声明

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

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