MySQL连接查询
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连接查询
有两个如下表：
mysql> select * from user; +---------+--------+---------------------+ | user_id | cos_id | user_creation_date | +---------+--------+---------------------+ | a | 3 | 2016-02-18 17:56:12 | | a1 | 1 | 2016-02-15 15:27:28 | | a2 | 1 | 2016-02-16 10:41:21 | | admin | 1 | 2016-02-15 10:47:51 | | q1 | 1 | 2016-02-21 13:17:05 | | q2 | 1 | 2016-02-21 13:17:05 | | q3 | 1 | 2016-02-21 13:17:05 | +---------+--------+---------------------+ 7 rows in set (0.00 sec) mysql> select * from password; +---------+------------------------------------+ | user_id | password | +---------+------------------------------------+ | admin | {enc8}IF8xUQIn+WSE4NBSSbTNUlc8wVY= | | a1 | {enc8}3t8+Udt7qGZB5eGvx1sYvuB9wVY= | | a2 | {enc8}sI5HqHAyktP0GYRfZ8YSQp1BxFY= | | a | NULL | | q1 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q2 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q3 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | +---------+------------------------------------+ 7 rows in set (0.00 sec)
内连接方法：
mysql> select user.user_id,cos_id,user_creation_date,password FROM user,password WHERE user.user_id=password.user_id; +---------+--------+---------------------+------------------------------------+ | user_id | cos_id | user_creation_date | password | +---------+--------+---------------------+------------------------------------+ | admin | 1 | 2016-02-15 10:47:51 | {enc8}IF8xUQIn+WSE4NBSSbTNUlc8wVY= | | a1 | 1 | 2016-02-15 15:27:28 | {enc8}3t8+Udt7qGZB5eGvx1sYvuB9wVY= | | a2 | 1 | 2016-02-16 10:41:21 | {enc8}sI5HqHAyktP0GYRfZ8YSQp1BxFY= | | a | 3 | 2016-02-18 17:56:12 | NULL | | q1 | 1 | 2016-02-21 13:17:05 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q2 | 1 | 2016-02-21 13:17:05 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q3 | 1 | 2016-02-21 13:17:05 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | +---------+--------+---------------------+------------------------------------+ 7 rows in set (0.00 sec)
外连接方法
分为左连接和右连接LEFT|RIGHT JOIN
有两个表如下：
mysql> SELECT * FROM user; +---------+--------+---------------------+ | user_id | cos_id | user_creation_date | +---------+--------+---------------------+ | a | 3 | 2016-02-18 17:56:12 | | a1 | 1 | 2016-02-15 15:27:28 | | a2 | 1 | 2016-02-16 10:41:21 | | admin | 1 | 2016-02-15 10:47:51 | | q1 | 1 | 2016-02-21 13:17:05 | | q2 | 1 | 2016-02-21 13:17:05 | | q3 | 1 | 2016-02-21 13:17:05 | +---------+--------+---------------------+ 7 rows in set (0.00 sec) mysql> SELECT * FROM pass; +---------+------------------------------------+ | user_id | password | +---------+------------------------------------+ | admin | {enc8}IF8xUQIn+WSE4NBSSbTNUlc8wVY= | | a1 | {enc8}3t8+Udt7qGZB5eGvx1sYvuB9wVY= | | a2 | {enc8}sI5HqHAyktP0GYRfZ8YSQp1BxFY= | | a | NULL | | q1 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q2 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q3 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | q4 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | q5 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | q6 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | q7 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | +---------+------------------------------------+ 11 rows in set (0.00 sec)
1、进行左连接查询
mysql> SELECT * FROM user LEFT JOIN pass ON user.user_id=pass.user_id; +---------+--------+---------------------+---------+------------------------------------+ | user_id | cos_id | user_creation_date | user_id | password | +---------+--------+---------------------+---------+------------------------------------+ | a | 3 | 2016-02-18 17:56:12 | a | NULL | | a1 | 1 | 2016-02-15 15:27:28 | a1 | {enc8}3t8+Udt7qGZB5eGvx1sYvuB9wVY= | | a2 | 1 | 2016-02-16 10:41:21 | a2 | {enc8}sI5HqHAyktP0GYRfZ8YSQp1BxFY= | | admin | 1 | 2016-02-15 10:47:51 | admin | {enc8}IF8xUQIn+WSE4NBSSbTNUlc8wVY= | | q1 | 1 | 2016-02-21 13:17:05 | q1 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q2 | 1 | 2016-02-21 13:17:05 | q2 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q3 | 1 | 2016-02-21 13:17:05 | q3 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | +---------+--------+---------------------+---------+------------------------------------+ 7 rows in set (0.00 sec)
2、进行右连接查询
mysql> SELECT * FROM user RIGHT JOIN pass ON user.user_id=pass.user_id; +---------+--------+---------------------+---------+------------------------------------+ | user_id | cos_id | user_creation_date | user_id | password | +---------+--------+---------------------+---------+------------------------------------+ | admin | 1 | 2016-02-15 10:47:51 | admin | {enc8}IF8xUQIn+WSE4NBSSbTNUlc8wVY= | | a1 | 1 | 2016-02-15 15:27:28 | a1 | {enc8}3t8+Udt7qGZB5eGvx1sYvuB9wVY= | | a2 | 1 | 2016-02-16 10:41:21 | a2 | {enc8}sI5HqHAyktP0GYRfZ8YSQp1BxFY= | | a | 3 | 2016-02-18 17:56:12 | a | NULL | | q1 | 1 | 2016-02-21 13:17:05 | q1 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q2 | 1 | 2016-02-21 13:17:05 | q2 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q3 | 1 | 2016-02-21 13:17:05 | q3 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | NULL | NULL | NULL | q4 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | NULL | NULL | NULL | q5 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | NULL | NULL | NULL | q6 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | | NULL | NULL | NULL | q7 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | +---------+--------+---------------------+---------+------------------------------------+ 11 rows in set (0.00 sec)
复合查询：
在查询条件后面继续加入其他条件可以让结果更加精确
mysql> select user.user_id,cos_id,user_creation_date,password FROM user,password WHERE user.user_id=password.user_id AND cos_id != 3; +---------+--------+---------------------+------------------------------------+ | user_id | cos_id | user_creation_date | password | +---------+--------+---------------------+------------------------------------+ | admin | 1 | 2016-02-15 10:47:51 | {enc8}IF8xUQIn+WSE4NBSSbTNUlc8wVY= | | a1 | 1 | 2016-02-15 15:27:28 | {enc8}3t8+Udt7qGZB5eGvx1sYvuB9wVY= | | a2 | 1 | 2016-02-16 10:41:21 | {enc8}sI5HqHAyktP0GYRfZ8YSQp1BxFY= | | q1 | 1 | 2016-02-21 13:17:05 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q2 | 1 | 2016-02-21 13:17:05 | {enc8}4X3Rf0UqSpFh61bNRsisNlFIyVY= | | q3 | 1 | 2016-02-21 13:17:05 | {enc8}wuHVCTVL+shkSrIFkvEStFJIyVY= | +---------+--------+---------------------+------------------------------------+ 6 rows in set (0.00 sec)
参考书籍：《MySQL入门很简单》
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