我有这两个表具有相同的密钥ID,但其中一个具有比另一个更多的记录,因此内部联接不起作用。我的查询结果只显示了两个表的常见记录:
t1:
---------------------
id, data
----------------------
1,aaa
2,bbb
4,ccc
t2:
-------------------
id
-------------------
1
2
3
4
5
join result :
-------------------
1,aaa
2,bbb
3,null
4,ccc
5,null
此查询不起作用:
$query=" SELECT t2.id, t1.data FROM table1 t1
INNER JOIN table2 t2
ON t1.id = t2.id
ORDER BY t2.id " ;
mysql> create table t1(id int,data varchar(20));
Query OK, 0 rows affected (0.36 sec)
mysql> insert into t1 values(1,'aaa'),(2,'bbb'),(4,'ccc');
Query OK, 3 rows affected (0.04 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> create table t2(id int);
Query OK, 0 rows affected (0.36 sec)
mysql> insert into t2 values(1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.06 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select t2.id,t1.data from t2 left join t1 on (t2.id = t1.id);
+------+------+
| id | data |
+------+------+
| 1 | aaa |
| 2 | bbb |
| 4 | ccc |
| 3 | NULL |
| 5 | NULL |
+------+------+
5 rows in set (0.00 sec)
mysql>
请试试这个。
$query=" SELECT t2.id, t1.data FROM table1 t1
RIGHT JOIN table2 t2
ON t1.id = t2.id
ORDER BY t2.id" ;
好吧,您提供的查询按照INNER JOIN
操作的预期工作。
SELECT t2.id, t1.data
FROM table1 t1
INNER JOIN table2 t2
ON t1.id = t2.id
ORDER BY t2.id
会产生:
| id | data |
| 1 | aaa |
| 2 | bbb |
| 4 | ccc |
如果你想查看第二个表中的所有值,你需要在LEFT JOIN
表上进行table2
操作。
SELECT t2.id, t1.data
FROM table2 t2
LEFT JOIN table1 t1
ON t1.id = t2.id
会产生:
| id | data |
| 1 | aaa |
| 2 | bbb |
| 3 | (null) |
| 4 | ccc |
| 5 | (null) |