如何在MySQL中使用Straight Join？

MySQL中的Straight join类似于inner join或join。这意味着它仅返回匹配行。首先，我们需要了解MySQL中的Straight join。为此，我们需要创建两个表，并使用外键约束将两个表关联起来。

这是第一个表

mysql> CREATE table ForeignTableDemo
-> (
-> Id int,
-> Name varchar(100),
-> FK int
-> );
Query OK, 0 rows affected (0.47 sec)

这是第二个表 –

mysql> CREATE table PrimaryTableDemo
-> (
-> FK int,
-> Address varchar(100),
-> primary key(FK)
-> );
Query OK, 0 rows affected (0.47 sec)

此后，我们将添加约束 –

mysql> ALTER table ForeignTableDemo add constraint FKConst foreign key(FK) references
PrimaryTableDemo(FK);
Query OK, 0 rows affected (1.54 sec)
Records: 0 Duplicates: 0 Warnings: 0

现在将记录添加到第二个表中 –

mysql> INSERT into PrimaryTableDemo values(1,'US');
Query OK, 1 row affected (0.10 sec)

mysql> INSERT into PrimaryTableDemo values(2,'UK');
Query OK, 1 row affected (0.14 sec)

mysql> INSERT into PrimaryTableDemo values(3,'Unknown');
Query OK, 1 row affected (0.08 sec)

阅读更多：MySQL 教程

显示记录

mysql> SELECT * from PrimaryTableDemo;

以下是输出 –

+----+---------+
| FK | Address |
+----+---------+
| 1  | US      |
| 2  | UK      |
| 3 | Unknown  |
+----+---------+
3 rows in set (0.00 sec)

现在，将记录添加到第一个表中

mysql> INSERT into ForeignTableDemo values (1,'John',1);
Query OK, 1 row affected (0.20 sec)

mysql> INSERT into ForeignTableDemo values (2,'Bob',2);
Query OK, 1 row affected (0.27 sec)

使用SELECT语句显示所有记录 –

mysql> SELECT * from ForeignTableDemo;

以下是输出

+------+------+------+
| Id   | Name | FK   |
+------+------+------+
| 1    | John | 1    |
| 2    | Bob  | 2    |
+------+------+------+
2 rows in set (0.00 sec)

Straight join查询的查询方式如下，仅显示匹配行 –

mysql>SELECT ForeignTableDemo.Id, ForeignTableDemo.Name, PrimaryTableDemo.Address
-> from ForeignTableDemo
-> Straight_join PrimaryTableDemo
-> on ForeignTableDemo.FK = PrimaryTableDemo.FK;

以下是输出 –

+------+------+---------+
| Id   | Name | Address |
+------+------+---------+
| 1    | John | US      |
| 2    | Bob  | UK      |
+------+------+---------+
2 rows in set (0.00 sec)