通用测试表
-- 学生表
CREATE TABLE student (
SNO INT,
SNAME VARCHAR(10),
ICNO INT
);
-- 食堂IC卡表
CREATE TABLE IC (
ICNO INT,
ICNAME VARCHAR(10),
ICMoney INT
);
INSERT INTO student
SELECT 1, '张三', 1 UNION ALL
SELECT 2, '李四', 2 UNION ALL
SELECT 3, '王五', NULL;
INSERT INTO IC
SELECT 1, '张三', 500 UNION ALL
SELECT 2, '李四', 250 UNION ALL
SELECT 3, '赵老师', 600;
INNER JOIN
Oracle 、SQL Server、MySQL 基本上无差别,仅仅演示一种数据库结果:
(INNER 可省略)
mysql> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> JOIN IC
-> ON (student.ICNO = IC.ICNO);
+------+-------+--------+---------+
| SNO | SNAME | ICNAME | ICMoney |
+------+-------+--------+---------+
| 1 | 张三 | 张三 | 500 |
| 2 | 李四 | 李四 | 250 |
+------+-------+--------+---------+
2 rows in set (0.00 sec)
LEFT OUTER JOIN
Oracle 、SQL Server、MySQL 基本上无差别,仅仅演示一种数据库结果:
(OUTER 可省略)
mysql> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> LEFT JOIN IC
-> ON (student.ICNO = IC.ICNO);
+------+-------+--------+---------+
| SNO | SNAME | ICNAME | ICMoney |
+------+-------+--------+---------+
| 1 | 张三 | 张三 | 500 |
| 2 | 李四 | 李四 | 250 |
| 3 | 王五 | NULL | NULL |
+------+-------+--------+---------+
3 rows in set (0.00 sec)
RIGHT OUTER JOIN
Oracle 、SQL Server、MySQL 基本上无差别,仅仅演示一种数据库结果:
(OUTER 可省略)
mysql> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> RIGHT JOIN IC
-> ON (student.ICNO = IC.ICNO);
+------+-------+--------+---------+
| SNO | SNAME | ICNAME | ICMoney |
+------+-------+--------+---------+
| 1 | 张三 | 张三 | 500 |
| 2 | 李四 | 李四 | 250 |
| NULL | NULL | 赵老师 | 600 |
+------+-------+--------+---------+
3 rows in set (0.00 sec)
CROSS JOIN
Oracle 、SQL Server、MySQL 基本上无差别,仅仅演示一种数据库结果:
mysql> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> CROSS JOIN IC;
+------+-------+--------+---------+
| SNO | SNAME | ICNAME | ICMoney |
+------+-------+--------+---------+
| 1 | 张三 | 张三 | 500 |
| 2 | 李四 | 张三 | 500 |
| 3 | 王五 | 张三 | 500 |
| 1 | 张三 | 李四 | 250 |
| 2 | 李四 | 李四 | 250 |
| 3 | 王五 | 李四 | 250 |
| 1 | 张三 | 赵老师 | 600 |
| 2 | 李四 | 赵老师 | 600 |
| 3 | 王五 | 赵老师 | 600 |
+------+-------+--------+---------+
9 rows in set (0.08 sec)
FULL JOIN
Oracle / SQL Server 支持 Full JOIN
(OUTER 可省略)
1> SELECT
2> student.SNO,
3> student.SNAME,
4> IC.ICNAME,
5> IC.ICMoney
6> FROM
7> student
8> FULL JOIN IC
9> ON (student.ICNO = IC.ICNO);
10> go
SNO SNAME ICNAME ICMoney
----------- ---------- ---------- -----------
1 张三 张三 500
2 李四 李四 250
3 王五 NULL NULL
NULL NULL 赵老师 600
(4 行受影响)
MySQL 好像是不支持
mysql> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> FULL JOIN IC
-> ON (student.ICNO = IC.ICNO);
ERROR 1054 (42S22): Unknown column 'student.SNO' in 'field list'
变通着,修改为
LEFT JOIN + UNION + RIGHT JOIN 的方式。
mysql> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> LEFT JOIN IC
-> ON (student.ICNO = IC.ICNO)
-> UNION
-> SELECT
-> student.SNO,
-> student.SNAME,
-> IC.ICNAME,
-> IC.ICMoney
-> FROM
-> student
-> RIGHT JOIN IC
-> ON (student.ICNO = IC.ICNO);
+------+-------+--------+---------+
| SNO | SNAME | ICNAME | ICMoney |
+------+-------+--------+---------+
| 1 | 张三 | 张三 | 500 |
| 2 | 李四 | 李四 | 250 |
| 3 | 王五 | NULL | NULL |
| NULL | NULL | 赵老师 | 600 |
+------+-------+--------+---------+
4 rows in set (0.01 sec)