MySQL 如何模拟数组变量？

使用MySQL中的临时表来模拟数组变量，语法如下 –

create temporary table if not exists yourTemporaryTableName
select yourColumnName1,yourColumnName2,......N from yourTableName where condition

为了理解上述语法，先创建一个表格。创建表格的查询如下 –

mysql> create table SimulateArrayDemo
   -> (
   -> Id int,
   -> FirstName varchar(100),
   -> LastName varchar(100
   -> )
   -> );
Query OK, 0 rows affected (1.25 sec)

使用 insert 命令向表格中插入一些记录。查询如下 –

mysql> insert into SimulateArrayDemo values(1,'Sam','Taylor');
Query OK, 1 row affected (0.10 sec)

mysql> insert into SimulateArrayDemo values(2,'Carol','Taylor');
Query OK, 1 row affected (0.18 sec)

mysql> insert into SimulateArrayDemo values(3,'Bob','Smith');
Query OK, 1 row affected (0.09 sec)

mysql> insert into SimulateArrayDemo values(4,'David','Taylor');
Query OK, 1 row affected (0.16 sec)

mysql> insert into SimulateArrayDemo values(5,'John','Smith');
Query OK, 1 row affected (0.11 sec)

mysql> insert into SimulateArrayDemo values(6,'Mike','Taylor');
Query OK, 1 row affected (0.21 sec)

使用 select 命令从表格中显示所有记录。查询如下 –

mysql> select *from SimulateArrayDemo;

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输出

+------+-----------+----------+
| Id   | FirstName | LastName |
+------+-----------+----------+
|    1 | Sam       | Taylor   |
|    2 | Carol     | Taylor   |
|    3 | Bob       | Smith    |
|    4 | David     | Taylor   |
|    5 | John      | Smith    |
|    6 | Mike      | Taylor   |
+------+-----------+----------+
6 rows in set (0.00 sec)

下面是使用临时表模拟数组变量的查询 –

mysql> create temporary table if not exists SimulationOfArray
   -> select Id,FirstName from SimulateArrayDemo where LastName='Taylor';
Query OK, 4 rows affected (0.10 sec)
Records: 4 Duplicates: 0 Warnings: 0

显示来自临时表的记录。查询如下 –

mysql> select *from SimulationOfArray;

输出

+------+-----------+
| Id   | FirstName |
+------+-----------+
|    1 | Sam       |
|    2 | Carol     |
|    4 | David     |
|    6 | Mike      |
+------+-----------+
4 rows in set (0.00 sec)