MySQL查询中输入参数（变量）的语法是什么？

在MySQL中设置变量，需要使用SET命令。以下是语法：

set @yourVariableName:=yourValue;
select *from yourTableName where yourColumnName=@yourVariableName;

让我们首先创建一个表：

mysql> create table DemoTable
(
   Id int,
   FirstName varchar(20),
   LastName varchar(20)
);
Query OK, 0 rows affected (0.83 sec)

以下是使用insert命令将记录插入表中的查询语句：

mysql> insert into DemoTable values(10,'Carol','Taylor');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable values(20,'John','Doe');
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable values(30,'John','Smith');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values(40,'David','Miller');
Query OK, 1 row affected (0.18 sec)

以下是使用select命令从表中显示记录的查询语句：

mysql> select *from DemoTable;

这将产生以下输出：

+------+-----------+----------+
| Id   | FirstName | LastName |
+------+-----------+----------+
| 10   | Carol     | Taylor   |
| 20   | John      | Doe      |
| 30   | John      | Smith    |
| 40   | David     | Miller   |
+------+-----------+----------+
4 rows in set (0.00 sec)

现在让我们看一下如何在MySQL中设置用户定义的变量：

mysql> set @myId:=30;
Query OK, 0 rows affected (0.00 sec)
mysql> select *from DemoTable where Id=@myId;

这将产生以下输出：

+------+-----------+----------+
| Id   | FirstName | LastName |
+------+-----------+----------+
| 30   | John      | Smith    |
+------+-----------+----------+
1 row in set (0.00 sec)

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