What is the difference in between
两者之间有什么区别
set test_var = 20;
and
和
set test_var:=20;
as they both seem to assign the value ?
因为他们似乎都分配了价值？
3 个解决方案
#1
9
Both of them are assignment operators but one thing I can find their differences is that = can be used to perform boolean operation while := cannot.
它们都是赋值运算符，但有一点我可以发现它们的区别在于=可以用于执行布尔运算，而：=不能。
valid: SUM(val = 0)
Invalid: SUM(val := 0)
有效：SUM（val = 0）无效：SUM（val：= 0）
来自用户定义的变量
One more thing, 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.
还有一件事，您还可以在SET以外的语句中为用户变量赋值。在这种情况下，赋值运算符必须是：=而不是=因为后者在非SET语句中被视为比较运算符=。
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 |
+------+------+------+--------------------+
#2
8
It's more or less Syntactic sugar.
它或多或少是句法糖。
Take a look here
看看这里
Most important difference is
最重要的区别是
Unlike =, the := operator is never interpreted as a comparison operator. This means you can use := in any valid SQL statement (not just in SET statements) to assign a value to a variable.
与=不同，：=运算符永远不会被解释为比较运算符。这意味着您可以在任何有效的SQL语句中使用：=（而不仅仅是在SET语句中）为变量赋值。
#3
1
You can only use := for assignment - never for comparison. It's just a bit of syntactic sugar, it doesn't really change the functionality at all. You'll see it a lot in generated SQL from code.
您只能使用：=进行分配 - 永远不会用于比较。它只是一些语法糖，它根本没有真正改变功能。你会从代码生成的SQL中看到很多东西。
#1
9
Both of them are assignment operators but one thing I can find their differences is that = can be used to perform boolean operation while := cannot.
它们都是赋值运算符，但有一点我可以发现它们的区别在于=可以用于执行布尔运算，而：=不能。
valid: SUM(val = 0)
Invalid: SUM(val := 0)
有效：SUM（val = 0）无效：SUM（val：= 0）
来自用户定义的变量
One more thing, 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.
还有一件事，您还可以在SET以外的语句中为用户变量赋值。在这种情况下，赋值运算符必须是：=而不是=因为后者在非SET语句中被视为比较运算符=。
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 |
+------+------+------+--------------------+
#2
8
It's more or less Syntactic sugar.
它或多或少是句法糖。
Take a look here
看看这里
Most important difference is
最重要的区别是
Unlike =, the := operator is never interpreted as a comparison operator. This means you can use := in any valid SQL statement (not just in SET statements) to assign a value to a variable.
与=不同，：=运算符永远不会被解释为比较运算符。这意味着您可以在任何有效的SQL语句中使用：=（而不仅仅是在SET语句中）为变量赋值。
#3
1
You can only use := for assignment - never for comparison. It's just a bit of syntactic sugar, it doesn't really change the functionality at all. You'll see it a lot in generated SQL from code.
您只能使用：=进行分配 - 永远不会用于比较。它只是一些语法糖，它根本没有真正改变功能。你会从代码生成的SQL中看到很多东西。