What's the difference between DECLARE and SET using SQL (or more specifically MySQL)?
使用SQL(或更具体的MySQL)DECLARE和SET之间有什么区别?
Both can set variables it seems. I have read the MySQL docs and I did not understand the difference between the two.
两者都可以设置变量。我已阅读MySQL文档,我不明白两者之间的区别。
2 个解决方案
#1
4
DECLARE does not initialize the variable. When you declare it you declare the variable name, the type, and a default value, which could be an expression.
DECLARE不初始化变量。声明它时,您声明变量名称,类型和默认值,它可以是表达式。
SET is for initializing the variable you declared previously, and you cannot SET the variable until you DECLARE it.
SET用于初始化您之前声明的变量,并且在DECLARE它之前不能设置变量。
#2
3
DECLARE defines the variable type and SET initializes the variable.
DECLARE定义变量类型,SET初始化变量。
DECLARE @Var1 INT;
DECLARE @Var2 INT;
SET @Var1 = 1;
SET @Var2 = 2;
#1
4
DECLARE does not initialize the variable. When you declare it you declare the variable name, the type, and a default value, which could be an expression.
DECLARE不初始化变量。声明它时,您声明变量名称,类型和默认值,它可以是表达式。
SET is for initializing the variable you declared previously, and you cannot SET the variable until you DECLARE it.
SET用于初始化您之前声明的变量,并且在DECLARE它之前不能设置变量。
#2
3
DECLARE defines the variable type and SET initializes the variable.
DECLARE定义变量类型,SET初始化变量。
DECLARE @Var1 INT;
DECLARE @Var2 INT;
SET @Var1 = 1;
SET @Var2 = 2;