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