Mysql数据库（五）表记录的检索
一、基本查询语句
二、单表查询
1.查询所有字段
mysql> SELECT * FROM tb_bookinfo;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec)
2.查询指定字段
mysql> SELECT bookname,author FROM tb_bookinfo;
+-----------+-----------+
| bookname | author |
+-----------+-----------+
| Java King | LianJiang |
| Lian | QiaoJiang |
| Tian King | TianJiang |
+-----------+-----------+
3 rows in set (0.00 sec)
3.查询指定数据
mysql> SELECT * FROM tb_bookinfo WHERE bookname='Tian King';
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
1 row in set (0.00 sec)
4.带IN关键字的查询
mysql> SELECT bookname,author,price,page,bookcase FROM tb_bookinfo WHERE bookcase IN(1,2);
+-----------+-----------+-------+------+----------+
| bookname | author | price | page | bookcase |
+-----------+-----------+-------+------+----------+
| Java King | LianJiang | 49.80 | 350 | 1 |
| Lian | QiaoJiang | 50.00 | 351 | 2 |
+-----------+-----------+-------+------+----------+
2 rows in set (0.00 sec) mysql> SELECT bookname,author,price,page,bookcase FROM tb_bookinfo WHERE bookcase IN(1,3);
+-----------+-----------+-------+------+----------+
| bookname | author | price | page | bookcase |
+-----------+-----------+-------+------+----------+
| Java King | LianJiang | 49.80 | 350 | 1 |
| Tian King | TianJiang | 51.10 | 352 | 3 |
+-----------+-----------+-------+------+----------+
2 rows in set (0.00 sec)
5.带BETWEEN AND的范围查询
mysql> SELECT * FROM tb_bookinfo WHERE inTime BETWEEN '2017-04-17' and '2017-04-19';
Empty set (0.00 sec) mysql> SELECT * FROM tb_bookinfo WHERE inTime BETWEEN '2018-04-17' and '2018-04-19';
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec) mysql> SELECT * FROM tb_bookinfo WHERE inTime BETWEEN '2018-04-17' and '2018-04-18';
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
2 rows in set (0.00 sec) mysql> SELECT * FROM tb_bookinfo WHERE inTime NOT BETWEEN '2018-04-17' and '2018-04-18';
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
1 row in set (0.00 sec)
6.带LIKE的字符匹配查询，通过它可以实现模糊查询，有两种通配符：%（可以匹配一个或多个字符，可以代表任意长度的字符串）和_（只匹配一个字符）
mysql> SELECT * FROM tb_bookinfo WHERE barcode LIKE '%71%';
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec)
7.用IS NULL关键字查询空值
mysql> SELECT * FROM tb_bookinfo WHERE bookname IS NULL;
Empty set (0.00 sec)
8.带AND的多条件查询
mysql> SELECT * FROM tb_bookinfo WHERE bookcase=1 AND del=0;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
1 row in set (0.00 sec)
9.带OR的多条件查询
mysql> SELECT * FROM tb_bookinfo WHERE bookcase=1 OR bookcase=2;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
2 rows in set (0.00 sec)
10.用DISTINCT关键字去除结果中的重复行
mysql> SELECT DISTINCT del FROM tb_bookinfo ;
+------+
| del |
+------+
| 0 |
+------+
1 row in set (0.00 sec)
11.用ORDER BY关键字对查询结果排序（ASC表示升序，DESC表示降序）
mysql> SELECT * FROM tb_bookinfo ORDER BY price DESC;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec)
mysql> SELECT * FROM tb_bookinfo ORDER BY typeid ASC;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec)
12.用GROUP BY关键字分组查询
（1）使用GROUP BY关键字分组查询
mysql> SELECT del,COUNT(*) FROM tb_bookinfo GROUP BY del;
+------+----------+
| del | COUNT(*) |
+------+----------+
| 0 | 3 |
+------+----------+
1 row in set (0.00 sec)
（2）GROUP BY关键字与GROUP_CONCAT()函数一起使用
mysql> SELECT del,GROUP_CONCAT(barcode) FROM tb_bookinfo GROUP BY del;
+------+----------------------------+
| del | GROUP_CONCAT(barcode) |
+------+----------------------------+
| 0 | 17120107,17120108,17120109 |
+------+----------------------------+
1 row in set (0.00 sec)
（3）按多个字段进行分组，当第一个字段有相同值时，再按第二个字段进行分组
mysql> SELECT del,barcode FROM tb_bookinfo GROUP BY del,barcode;
+------+----------+
| del | barcode |
+------+----------+
| 0 | 17120107 |
| 0 | 17120108 |
| 0 | 17120109 |
+------+----------+
3 rows in set (0.00 sec)
13.用LIMIT限制查询结果的数量(显示前两条数据和从第1个编号开始（记录编号是从0开始的），查询两条数据)
mysql> SELECT * FROM tb_bookinfo ORDER BY price DESC LIMIT 2;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
2 rows in set (0.00 sec)
mysql> SELECT * FROM tb_bookinfo ORDER BY price DESC LIMIT 1,2;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
2 rows in set (0.00 sec)
三、聚合函数查询
聚合函数的最大特点是它们根据一组数据求出一个值。聚合函数的结果值只根据选定行中非NULL的值进行计算，NULL值被忽略。
1.COUNT()函数用于对除“*”以外的任何参数，返回所选择集合中非NULL值的行的数目；对于参数“*”，返回选择集合中所有行的数目，包含NULL值的行。
mysql> SELECT COUNT(*) FROM tb_bookinfo;
+----------+
| COUNT(*) |
+----------+
| 3 |
+----------+
1 row in set (0.00 sec)
2.SUM()函数
mysql> SELECT price FROM tb_bookinfo;
+-------+
| price |
+-------+
| 49.80 |
| 50.00 |
| 51.10 |
+-------+
3 rows in set (0.00 sec) mysql> SELECT SUM(price) FROM tb_bookinfo;
+------------+
| SUM(price) |
+------------+
| 150.90 |
+------------+
1 row in set (0.00 sec)
3.AVG()函数
mysql> SELECT AVG(price) FROM tb_bookinfo;
+------------+
| AVG(price) |
+------------+
| 50.299999 |
+------------+
1 row in set (0.00 sec)
4.MAX()函数
mysql> SELECT MAX(price) FROM tb_bookinfo;
+------------+
| MAX(price) |
+------------+
| 51.10 |
+------------+
1 row in set (0.00 sec)
5.MIN()函数
mysql> SELECT MIN(price) FROM tb_bookinfo;
+------------+
| MIN(price) |
+------------+
| 49.80 |
+------------+
1 row in set (0.00 sec)
四、连接查询
1.内连接查询
连接是把不同表的记录连到一起的最普遍的方法。内连接是最普遍的连接类型，而且是最匀称的，因为它们要求构成连接的每个表的共有列匹配，不匹配的行将被排除。内连接包括相等连接和自然连接，最常见的例子是相等连接，也就是使用等号运算符根据每个表共有的列的值匹配两个表的行。这种情况下，最后的结果集只包含参加连接的表中与指定字段相符的行。
mysql> SELECT * FROM tb_bookinfo;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec) mysql> SELECT * FROM tb_borrow;
+----+----------+--------+------------+------------+----------+--------+
| id | readerid | bookid | borrowTime | backTime | operator | ifback |
+----+----------+--------+------------+------------+----------+--------+
| 1 | 1 | 1 | 2018-04-17 | 2018-04-20 | mr | 1 |
| 2 | 1 | 2 | 2018-04-16 | 2018-04-21 | mr | 1 |
+----+----------+--------+------------+------------+----------+--------+
2 rows in set (0.00 sec) mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_borrow,tb_bookinfo WHERE tb_borrow.bookid=tb_bookinfo.id;
+--------+------------+------------+--------+-----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+-----------+-----------+-------+
| 1 | 2018-04-17 | 2018-04-20 | 1 | Java King | LianJiang | 49.80 |
| 2 | 2018-04-16 | 2018-04-21 | 1 | Lian | QiaoJiang | 50.00 |
+--------+------------+------------+--------+-----------+-----------+-------+
2 rows in set (0.00 sec)
2.外连接查询
与内连接不同，外连接是指使用OUTET JOIN关键字将两个表连接起来。外连接生成的结果集不仅包含符合连接条件的行数据，而且含包括左表、右表或两边连接表中所有的数据行。
（1）左外连接（这里要弄清楚左外连接和内连接的区别）
mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_borrow LEFT JOIN tb_bookinfo ON tb_borrow.bookid=tb_bookinfo.id;
+--------+------------+------------+--------+-----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+-----------+-----------+-------+
| 1 | 2018-04-17 | 2018-04-20 | 1 | Java King | LianJiang | 49.80 |
| 2 | 2018-04-16 | 2018-04-21 | 1 | Lian | QiaoJiang | 50.00 |
+--------+------------+------------+--------+-----------+-----------+-------+
2 rows in set (0.00 sec)
mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_bookinfo LEFT JOIN tb_borrow ON tb_borrow.bookid=tb_bookinfo.id;
+--------+------------+------------+--------+-----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+-----------+-----------+-------+
| 1 | 2018-04-17 | 2018-04-20 | 1 | Java King | LianJiang | 49.80 |
| 2 | 2018-04-16 | 2018-04-21 | 1 | Lian | QiaoJiang | 50.00 |
| NULL | NULL | NULL | NULL | Tian King | TianJiang | 51.10 |
+--------+------------+------------+--------+-----------+-----------+-------+
3 rows in set (0.00 sec)
（2）右外连接
mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_bookinfo RIGHT JOIN tb_borrow ON tb_borrow.bookid=tb_bookinfo.id;
+--------+------------+------------+--------+-----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+-----------+-----------+-------+
| 1 | 2018-04-17 | 2018-04-20 | 1 | Java King | LianJiang | 49.80 |
| 2 | 2018-04-16 | 2018-04-21 | 1 | Lian | QiaoJiang | 50.00 |
+--------+------------+------------+--------+-----------+-----------+-------+
2 rows in set (0.00 sec)
mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_borrow RIGHT JOIN tb_bookinfo ON tb_borrow.bookid=tb_bookinfo.id;
+--------+------------+------------+--------+-----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+-----------+-----------+-------+
| 1 | 2018-04-17 | 2018-04-20 | 1 | Java King | LianJiang | 49.80 |
| 2 | 2018-04-16 | 2018-04-21 | 1 | Lian | QiaoJiang | 50.00 |
| NULL | NULL | NULL | NULL | Tian King | TianJiang | 51.10 |
+--------+------------+------------+--------+-----------+-----------+-------+
3 rows in set (0.00 sec)
3.复合条件连接查询
mysql> UPDATE tb_borrow SET ifback=0 WHERE id=2;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0 mysql> SELECT * FROM tb_borrow;
+----+----------+--------+------------+------------+----------+--------+
| id | readerid | bookid | borrowTime | backTime | operator | ifback |
+----+----------+--------+------------+------------+----------+--------+
| 1 | 1 | 1 | 2018-04-17 | 2018-04-20 | mr | 1 |
| 2 | 1 | 2 | 2018-04-16 | 2018-04-21 | mr | 0 |
+----+----------+--------+------------+------------+----------+--------+
2 rows in set (0.00 sec) mysql> SELECT * FROM tb_bookinfo;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec) mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_bookinfo,tb_borrow WHERE tb_borrow.bookid=tb_bookinfo.id;
+--------+------------+------------+--------+-----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+-----------+-----------+-------+
| 1 | 2018-04-17 | 2018-04-20 | 1 | Java King | LianJiang | 49.80 |
| 2 | 2018-04-16 | 2018-04-21 | 0 | Lian | QiaoJiang | 50.00 |
+--------+------------+------------+--------+-----------+-----------+-------+
2 rows in set (0.00 sec)
mysql> SELECT bookid,borrowTime,backTime,ifback,bookname,author,price
-> FROM tb_bookinfo,tb_borrow WHERE tb_borrow.bookid=tb_bookinfo.id AND ifback=0;
+--------+------------+------------+--------+----------+-----------+-------+
| bookid | borrowTime | backTime | ifback | bookname | author | price |
+--------+------------+------------+--------+----------+-----------+-------+
| 2 | 2018-04-16 | 2018-04-21 | 0 | Lian | QiaoJiang | 50.00 |
+--------+------------+------------+--------+----------+-----------+-------+
1 row in set (0.00 sec)
五、子查询
MySQL可以嵌套多个查询，在外面一层的查询中使用里面一层查询产生的结果集。这样就不是执行两个独立地查询，而是执行包含一个（或者多个）子查询的单独查询。
1.带IN关键字的子查询
mysql> SELECT id FROM tb_bookinfo;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
+----+
3 rows in set (0.00 sec) mysql> SELECT bookid FROM tb_borrow;
+--------+
| bookid |
+--------+
| 1 |
| 2 |
+--------+
2 rows in set (0.00 sec) mysql> SELECT id,bookname,author,price
-> FROM tb_bookinfo WHERE id IN (SELECT bookid FROM tb_borrow);
+----+-----------+-----------+-------+
| id | bookname | author | price |
+----+-----------+-----------+-------+
| 1 | Java King | LianJiang | 49.80 |
| 2 | Lian | QiaoJiang | 50.00 |
+----+-----------+-----------+-------+
2 rows in set (0.01 sec)
mysql> SELECT id,bookname,author,price
-> FROM tb_bookinfo WHERE id NOT IN (SELECT bookid FROM tb_borrow);
+----+-----------+-----------+-------+
| id | bookname | author | price |
+----+-----------+-----------+-------+
| 3 | Tian King | TianJiang | 51.10 |
+----+-----------+-----------+-------+
1 row in set (0.00 sec)
2.带比较运算符的子查询
mysql>
mysql> SELECT * FROM tb_borrow;
+----+----------+--------+------------+------------+----------+--------+
| id | readerid | bookid | borrowTime | backTime | operator | ifback |
+----+----------+--------+------------+------------+----------+--------+
| 1 | 1 | 1 | 2018-04-17 | 2018-04-20 | mr | 1 |
| 2 | 1 | 2 | 2018-04-16 | 2018-04-21 | mr | 0 |
+----+----------+--------+------------+------------+----------+--------+
2 rows in set (0.00 sec) mysql> SELECT * FROM tb_bookinfo;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec) mysql> SELECT ifback FROM tb_borrow WHERE borrowTime='2018-04-17';
+--------+
| ifback |
+--------+
| 1 |
+--------+
1 row in set (0.00 sec)
mysql> SELECT * FROM tb_bookinfo
-> WHERE typeid > (SELECT ifback FROM tb_borrow WHERE borrowTime='2018-04-17');
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
2 rows in set (0.00 sec)
3.带EXISTS关键字的子查询
mysql> SELECT * FROM tb_borrow;
+----+----------+--------+------------+------------+----------+--------+
| id | readerid | bookid | borrowTime | backTime | operator | ifback |
+----+----------+--------+------------+------------+----------+--------+
| 1 | 1 | 1 | 2018-04-17 | 2018-04-20 | mr | 1 |
| 2 | 1 | 2 | 2018-04-16 | 2018-04-21 | mr | 0 |
+----+----------+--------+------------+------------+----------+--------+
2 rows in set (0.00 sec) mysql> SELECT * FROM tb_bookinfo;
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec)
mysql> SELECT id,bookname,author,price
-> FROM tb_bookinfo WHERE EXISTS (SELECT * FROM tb_borrow WHERE tb_borrow.bookid=tb_bookinfo.id);
+----+-----------+-----------+-------+
| id | bookname | author | price |
+----+-----------+-----------+-------+
| 1 | Java King | LianJiang | 49.80 |
| 2 | Lian | QiaoJiang | 50.00 |
+----+-----------+-----------+-------+
2 rows in set (0.01 sec)
mysql> SELECT id,bookname,author,price
-> FROM tb_bookinfo WHERE NOT EXISTS (SELECT * FROM tb_borrow WHERE tb_borrow.bookid=tb_bookinfo.id);
+----+-----------+-----------+-------+
| id | bookname | author | price |
+----+-----------+-----------+-------+
| 3 | Tian King | TianJiang | 51.10 |
+----+-----------+-----------+-------+
1 row in set (0.00 sec)
4.带ANY关键字的子查询
ANY关键字表示满足其中任意一个条件，通常与比较运算符一起使用，只要满足内层查询语句返回的结果中的任意一个，就可以通过该条件来执行外层查询语句。
<表示小于子查询结果集中某一个值；>表示至少大于子查询结果集中的某一个值。
mysql> SELECT * FROM tb_student;
+----+------+------+---------+-------+
| id | name | sex | classid | score |
+----+------+------+---------+-------+
| 1 | a | 男 | 1 | 199 |
| 2 | b | 女 | 3 | 150 |
| 3 | c | 女 | 2 | 199 |
| 4 | d | 男 | 2 | 188 |
| 5 | e | 女 | 5 | 198 |
| 6 | f | 女 | 5 | 200 |
+----+------+------+---------+-------+
6 rows in set (0.00 sec)
得到的结果是只要大于188都可以输出。
mysql> SELECT * FROM tb_student WHERE score > ANY (SELECT score FROM tb_student WHERE classid=2);
+----+------+------+---------+-------+
| id | name | sex | classid | score |
+----+------+------+---------+-------+
| 1 | a | 男 | 1 | 199 |
| 3 | c | 女 | 2 | 199 |
| 5 | e | 女 | 5 | 198 |
| 6 | f | 女 | 5 | 200 |
+----+------+------+---------+-------+
4 rows in set (0.00 sec)
得到的结果是只要比199小都输出。
mysql> SELECT * FROM tb_student WHERE score < ANY (SELECT score FROM tb_student WHERE classid=2);
+----+------+------+---------+-------+
| id | name | sex | classid | score |
+----+------+------+---------+-------+
| 2 | b | 女 | 3 | 150 |
| 4 | d | 男 | 2 | 188 |
| 5 | e | 女 | 5 | 198 |
+----+------+------+---------+-------+
3 rows in set (0.00 sec)
5.带ALL关键字的子查询
和ANY相反，<表示小于查询结果中的最小值，>表示大于查询结果中的最大值
mysql> SELECT * FROM tb_student WHERE score > ALL (SELECT score FROM tb_student WHERE classid=2);
+----+------+------+---------+-------+
| id | name | sex | classid | score |
+----+------+------+---------+-------+
| 6 | f | 女 | 5 | 200 |
+----+------+------+---------+-------+
1 row in set (0.00 sec) mysql> SELECT * FROM tb_student WHERE score < ALL (SELECT score FROM tb_student WHERE classid=2);
+----+------+------+---------+-------+
| id | name | sex | classid | score |
+----+------+------+---------+-------+
| 2 | b | 女 | 3 | 150 |
+----+------+------+---------+-------+
1 row in set (0.00 sec)
六、合并查询结果
1.使用UNION关键字
mysql> SELECT barcode FROM tb_bookinfo;
+----------+
| barcode |
+----------+
| 17120107 |
| 17120108 |
| 17120109 |
+----------+
3 rows in set (0.00 sec) mysql> SELECT barcode FROM tb_bookinfo_copy;
+----------+
| barcode |
+----------+
| 17120107 |
| 17120108 |
| 17120106 |
+----------+
3 rows in set (0.00 sec) mysql> SELECT barcode FROM tb_bookinfo UNION SELECT barcode FROM tb_bookinfo_copy;
+----------+
| barcode |
+----------+
| 17120107 |
| 17120108 |
| 17120109 |
| 17120106 |
+----------+
4 rows in set (0.00 sec)
2.使用UNION ALL关键字
mysql> SELECT barcode FROM tb_bookinfo UNION ALL SELECT barcode FROM tb_bookinfo_copy;
+----------+
| barcode |
+----------+
| 17120107 |
| 17120108 |
| 17120109 |
| 17120107 |
| 17120108 |
| 17120106 |
+----------+
6 rows in set (0.00 sec)
七、定义表和字段的别名
1.为表取别名
mysql> SELECT bookname,author,price,page
-> FROM tb_bookinfo AS book
-> LEFT JOIN tb_borrow AS type ON book.typeid=type.id;
+-----------+-----------+-------+------+
| bookname | author | price | page |
+-----------+-----------+-------+------+
| Java King | LianJiang | 49.80 | 350 |
| Lian | QiaoJiang | 50.00 | 351 |
| Tian King | TianJiang | 51.10 | 352 |
+-----------+-----------+-------+------+
3 rows in set (0.00 sec)
2.为字段取别名，统计del的次数并取别名为degree
mysql> SELECT del,COUNT(*) AS degree FROM tb_bookinfo GROUP BY del;
+------+--------+
| del | degree |
+------+--------+
| 0 | 3 |
+------+--------+
1 row in set (0.00 sec)
八、使用正则表达式查询
1.匹配指定字符集中任意一个（查询出bookname中包括字幕g或v）
mysql> SELECT * FROM tb_bookinfo
-> WHERE bookname REGEXP '[gv]';
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
2 rows in set (0.01 sec)
2.使用“*”和“+”来匹配多个字符（*表示匹配多个该符号之前的字符，包括0和1个；+表示匹配多个该符号之前的字符，包括一个）
mysql> SELECT email FROM tb_student;
+-----------------------+
| email |
+-----------------------+
| sjy534948129@sina.com |
| sjy.com |
| a.com |
| a.b.com |
| assdad |
| dadd.sda |
+-----------------------+
6 rows in set (0.00 sec) mysql> SELECT email FROM tb_student
-> WHERE email NOT REGEXP '^[a-zA-Z0-9_-]+@[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)+$';
+----------+
| email |
+----------+
| sjy.com |
| a.com |
| a.b.com |
| assdad |
| dadd.sda |
+----------+
5 rows in set (0.00 sec)
正则表达式的模式字符
1. ^ 匹配以特定字符或字符串开头的记录
2. $ 匹配以特定字符或字符串结尾的记录
3. . 匹配字符串的任意一个字符，包括回车和换行
4. [字符集合] 匹配'字符集合'中的任意一个字符
5. [^字符集合] 匹配除'字符集合'中的任意一个字符
6. S1|S2|S3 匹配S1、S2和S3中的任意一个字符串
7. * 匹配多个该符号之前的字符，包括0个和1个
8. + 匹配多个该符号之前的字符，包括1个
9. 字符串{N} 匹配字符串出现N次
10. 字符串{M，N} 匹配字符串出现至少M次，最多N次
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