Mysql学习之路07-子查询

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目录(?)[+]

子查询定义
子查询分类

21 按返回结果集分类
22 按照对返回结果的调用方法

使用子查询原则
实例分析

41 创建测试表
42 插入测试数据
43 表子查询实例
44 行子查询实例
45 标量子查询实例
46 列子查询实例
47 where型子查询
48 from型子查询
49 exists型子查询

1 子查询定义

在一个表表达中可以调用另一个表表达式，这个被调用的表表达式叫做子查询（subquery），我么也称作子选择（subselect）或内嵌选择（inner select）。子查询的结果传递给调用它的表表达式继续处理。

2 子查询分类

2.1 按返回结果集分类

子查询按返回结果集的不同分为4种：表子查询，行子查询，列子查询和标量子查询。
表子查询：返回的结果集是一个行的集合，N行N列（N>=1）。表子查询经常用于父查询的FROM子句中。
行子查询：返回的结果集是一个列的集合，一行N列（N>=1）。行子查询可以用于福查询的FROM子句和WHERE子句中。
列子查询：返回的结果集是一个行的集合，N行一列（N>=1）。

标量子查询：返回的结果集是一个标量集合，一行一列，也就是一个标量值。可以指定一个标量表达式的任何地方，都可以用一个标量子查询。

从定义上讲，每个标量子查询也是一个行子查询和一个列子查询，反之则不是；每个行子查询和列子查询也是一个表子查询，反之也不是。

2.2 按照对返回结果的调用方法

子查询按对返回结果集的调用方法，可分为where型子查询，from型子查询及exists型子查询。
where型子查询：（把内层查询结果当作外层查询的比较条件）
定义：where型的子查询就是把内层查询的结果当作外层查询的条件。
from型子查询：（把内层的查询结果供外层再次查询）
定义：from子查询就是把子查询的结果(内存里的一张表)当作一张临时表，然后再对它进行处理。
exists型子查询：（把外层查询结果拿到内层，看内层的查询是否成立）
定义：exists子查询就是对外层表进行循环，再对内表进行内层查询。和in ()差不多，但是它们还是有区别的。主要是看两个张表大小差的程度。若子查询表大则用exists（内层索引），子查询表小则用in（外层索引）；

3 使用子查询原则

1.一个子查询必须放在圆括号中。
2.将子查询放在比较条件的右边以增加可读性。
子查询不包含 ORDER BY 子句。对一个 SELECT 语句只能用一个 ORDER BY 子句，并且如果指定了它就必须放在主 SELECT 语句的最后。
3.在子查询中可以使用两种比较条件：单行运算符(>, =, >=, <, <>, <=) 和多行运算符(IN, ANY, ALL)。

4 实例分析

4.1 创建测试表

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CREATE TABLE PLAYERS
(PLAYERNO INTEGER NOT NULL,
NAME CHAR(15) NOT NULL,
INITIALS CHAR(3) NOT NULL,
BIRTH_DATE DATE ,
SEX CHAR(1) NOT NULL,
JOINED SMALLINT NOT NULL,
STREET VARCHAR(30) NOT NULL,
HOUSENO CHAR(4) ,
POSTCODE CHAR(6) ,
TOWN VARCHAR(30) NOT NULL,
PHONENO CHAR(13) ,
LEAGUENO CHAR(4) ,
PRIMARY KEY (PLAYERNO));
CREATE TABLE PENALTIES
(PAYMENTNO INTEGER NOT NULL,
PLAYERNO INTEGER NOT NULL,
PAYMENT_DATE DATE NOT NULL,
AMOUNT DECIMAL(7,2) NOT NULL,
PRIMARY KEY (PAYMENTNO));

CREATE TABLE PLAYERS    (PLAYERNO      INTEGER      NOT NULL,    NAME           CHAR(15)     NOT NULL,    INITIALS       CHAR(3)      NOT NULL,    BIRTH_DATE     DATE                 ,    SEX            CHAR(1)      NOT NULL,    JOINED         SMALLINT     NOT NULL,    STREET         VARCHAR(30)  NOT NULL,    HOUSENO        CHAR(4)              ,    POSTCODE       CHAR(6)              ,    TOWN           VARCHAR(30)  NOT NULL,    PHONENO        CHAR(13)             ,    LEAGUENO       CHAR(4)              ,    PRIMARY KEY    (PLAYERNO));CREATE   TABLE PENALTIES        (PAYMENTNO      INTEGER      NOT NULL,         PLAYERNO       INTEGER      NOT NULL,         PAYMENT_DATE   DATE         NOT NULL,         AMOUNT         DECIMAL(7,2) NOT NULL,         PRIMARY KEY    (PAYMENTNO));

注：表players为球员信息基本表，表penalties为有过罚款记录的球员信息列表。

4.2 插入测试数据

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INSERT INTO PLAYERS VALUES (2, ‘Everett’, ‘R’, ‘1948-09-01’, ‘M’, 1975, ‘Stoney Road’,‘43’, ‘3575NH’, ‘Stratford’, ‘070-237893’, ‘2411’);
INSERT INTO PLAYERS VALUES (6, ‘Parmenter’, ‘R’, ‘1964-06-25’, ‘M’, 1977, ‘Haseltine Lane’,‘80’, ‘1234KK’, ‘Stratford’, ‘070-476537’, ‘8467’);
INSERT INTO PLAYERS VALUES (7, ‘Wise’, ‘GWS’, ‘1963-05-11’, ‘M’, 1981, ‘Edgecombe Way’,‘39’, ‘9758VB’, ‘Stratford’, ‘070-347689’, NULL);
INSERT INTO PLAYERS VALUES (8, ‘Newcastle’, ‘B’, ‘1962-07-08’, ‘F’, 1980, ‘Station Road’,‘4’, ‘6584WO’, ‘Inglewood’, ‘070-458458’, ‘2983’);
INSERT INTO PLAYERS VALUES (27, ‘Collins’, ‘DD’, ‘1964-12-28’, ‘F’, 1983, ‘Long Drive’,‘804’, ‘8457DK’, ‘Eltham’, ‘079-234857’, ‘2513’);
INSERT INTO PLAYERS VALUES (28, ‘Collins’, ‘C’, ‘1963-06-22’, ‘F’, 1983, ‘Old Main Road’,‘10’, ‘1294QK’, ‘Midhurst’, ‘010-659599’, NULL);
INSERT INTO PLAYERS VALUES (39, ‘Bishop’, ‘D’, ‘1956-10-29’, ‘M’, 1980, ‘Eaton Square’,‘78’, ‘9629CD’, ‘Stratford’, ‘070-393435’, NULL);
INSERT INTO PLAYERS VALUES (44, ‘Baker’, ‘E’, ‘1963-01-09’, ‘M’, 1980, ‘Lewis Street’,‘23’, ‘4444LJ’, ‘Inglewood’, ‘070-368753’, ‘1124’);
INSERT INTO PLAYERS VALUES (57, ‘Brown’, ‘M’, ‘1971-08-17’, ‘M’, 1985, ‘Edgecombe Way’,‘16’, ‘4377CB’, ‘Stratford’, ‘070-473458’, ‘6409’);
INSERT INTO PLAYERS VALUES (83, ‘Hope’, ‘PK’, ‘1956-11-11’, ‘M’, 1982, ‘Magdalene Road’,‘16A’, ‘1812UP’, ‘Stratford’, ‘070-353548’, ‘1608’);
INSERT INTO PLAYERS VALUES (95, ‘Miller’, ‘P’, ‘1963-05-14’, ‘M’, 1972, ‘High Street’,‘33A’, ‘5746OP’, ‘Douglas’, ‘070-867564’, NULL);
INSERT INTO PLAYERS VALUES (100, ‘Parmenter’, ‘P’, ‘1963-02-28’, ‘M’, 1979, ‘Haseltine Lane’,‘80’, ‘6494SG’, ‘Stratford’, ‘070-494593’, ‘6524’);
INSERT INTO PLAYERS VALUES (104, ‘Moorman’, ‘D’, ‘1970-05-10’, ‘F’, 1984, ‘Stout Street’,‘65’, ‘9437AO’, ‘Eltham’, ‘079-987571’, ‘7060’);
INSERT INTO PLAYERS VALUES (112, ‘Bailey’, ‘IP’, ‘1963-10-01’, ‘F’, 1984, ‘Vixen Road’,‘8’, ‘6392LK’, ‘Plymouth’, ‘010-548745’, ‘1319’);
INSERT INTO PENALTIES VALUES (1, 6, ‘1980-12-08’,100);
INSERT INTO PENALTIES VALUES (2, 44, ‘1981-05-05’, 75);
INSERT INTO PENALTIES VALUES (3, 27, ‘1983-09-10’,100);
INSERT INTO PENALTIES VALUES (4,104, ‘1984-12-08’, 50);
INSERT INTO PENALTIES VALUES (5, 44, ‘1980-12-08’, 25);
INSERT INTO PENALTIES VALUES (6, 8, ‘1980-12-08’, 25);
INSERT INTO PENALTIES VALUES (7, 44, ‘1982-12-30’, 30);
INSERT INTO PENALTIES VALUES (8, 27, ‘1984-11-12’, 75);

INSERT INTO PLAYERS VALUES (2, 'Everett', 'R', '1948-09-01', 'M', 1975, 'Stoney Road','43', '3575NH', 'Stratford', '070-237893', '2411');INSERT INTO PLAYERS VALUES (6, 'Parmenter', 'R', '1964-06-25', 'M', 1977, 'Haseltine Lane','80', '1234KK', 'Stratford', '070-476537', '8467');INSERT INTO PLAYERS VALUES (7, 'Wise', 'GWS', '1963-05-11', 'M', 1981, 'Edgecombe Way','39', '9758VB', 'Stratford', '070-347689', NULL);INSERT INTO PLAYERS VALUES (8, 'Newcastle', 'B', '1962-07-08', 'F', 1980, 'Station Road','4', '6584WO', 'Inglewood', '070-458458', '2983');INSERT INTO PLAYERS VALUES (27, 'Collins', 'DD', '1964-12-28', 'F', 1983, 'Long Drive','804', '8457DK', 'Eltham', '079-234857', '2513');INSERT INTO PLAYERS VALUES (28, 'Collins', 'C', '1963-06-22', 'F', 1983, 'Old Main Road','10', '1294QK', 'Midhurst', '010-659599', NULL);INSERT INTO PLAYERS VALUES (39, 'Bishop', 'D', '1956-10-29', 'M', 1980, 'Eaton Square','78', '9629CD', 'Stratford', '070-393435', NULL);INSERT INTO PLAYERS VALUES (44, 'Baker', 'E', '1963-01-09', 'M', 1980, 'Lewis Street','23', '4444LJ', 'Inglewood', '070-368753', '1124');INSERT INTO PLAYERS VALUES (57, 'Brown', 'M', '1971-08-17', 'M', 1985, 'Edgecombe Way','16', '4377CB', 'Stratford', '070-473458', '6409');INSERT INTO PLAYERS VALUES (83, 'Hope', 'PK', '1956-11-11', 'M', 1982, 'Magdalene Road','16A', '1812UP', 'Stratford', '070-353548', '1608');INSERT INTO PLAYERS VALUES (95, 'Miller', 'P', '1963-05-14', 'M', 1972, 'High Street','33A', '5746OP', 'Douglas', '070-867564', NULL);INSERT INTO PLAYERS VALUES (100, 'Parmenter', 'P', '1963-02-28', 'M', 1979, 'Haseltine Lane','80', '6494SG', 'Stratford', '070-494593', '6524');INSERT INTO PLAYERS VALUES (104, 'Moorman', 'D', '1970-05-10', 'F', 1984, 'Stout Street','65', '9437AO', 'Eltham', '079-987571', '7060');INSERT INTO PLAYERS VALUES (112, 'Bailey', 'IP', '1963-10-01', 'F', 1984, 'Vixen Road','8', '6392LK', 'Plymouth', '010-548745', '1319');INSERT INTO PENALTIES VALUES (1,  6, '1980-12-08',100);INSERT INTO PENALTIES VALUES (2, 44, '1981-05-05', 75);INSERT INTO PENALTIES VALUES (3, 27, '1983-09-10',100);INSERT INTO PENALTIES VALUES (4,104, '1984-12-08', 50);INSERT INTO PENALTIES VALUES (5, 44, '1980-12-08', 25);INSERT INTO PENALTIES VALUES (6,  8, '1980-12-08', 25);INSERT INTO PENALTIES VALUES (7, 44, '1982-12-30', 30);INSERT INTO PENALTIES VALUES (8, 27, '1984-11-12', 75);

4.3 表子查询实例

如：获取编号小于10的男性球员的号码

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mysql> select playerno from (
select playerno, sex
from players
where playerno < 10)
as players10 where sex=‘M’;

mysql> select playerno from (    select playerno, sex     from players     where playerno < 10) as players10 where sex='M';

4.4 行子查询实例

如：获取和100号球员性别相同并且居住在同一城市的球员号码。

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mysql> select playerno
from players
where (sex, town) = (
select sex, town
from players
where playerno = 100);

mysql> select playerno from players where (sex, town) = (    select sex, town     from players     where playerno = 100);

说明：子查询的结果是带有两个值的一行：（’M’,’stratford’）。这个值和一个行表达式（sex,town）进行比较。

4.5 标量子查询实例

可以指定一个标量表达式的任何地方，几乎都可以使用一个标量子查询。
如：获取和27号球员出生在同一年的球员的号码

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mysql> select playerno
from players
where year(birth_date) =
(select year(birth_date)
from players
where playerno = 27)
and playerno <> 27;

mysql> select playerno from players where year(birth_date) =     (select year(birth_date)     from players     where playerno = 27) and playerno <> 27;

上面语句等同于：

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mysql> select playerno from players where year(birth_date) = 1964 and playerno <> 27;

mysql> select playerno from players where year(birth_date) = 1964 and playerno <> 27;

4.6 列子查询实例

由于列子查询返回的结果集是 N 行一列，因此不能直接使用 = > < >= <= <> 这些比较标量结果的操作符。在列子查询中可以使用 IN、ANY（SOME）和ALL操作符：
  IN：在指定项内，同 IN(项1,项2,…)。
  ANY：与比较操作符联合使用，ANY关键字必须接在一个比较操作符的后面，表示与子查询返回的任何值比较为 TRUE ，则返回 TRUE 。
  SOME：ANY 的别名，较少使用。
  ALL：与比较操作符联合使用，ALL关键字必须接在一个比较操作符的后面，表示与子查询返回的所有值比较都为 TRUE ，则返回 TRUE 。

实例1（in）：获取球员性别为女的所有球员的球员号，名字及所在城市。

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mysql> select playerno, name, town
from players
where playerno in
(select playerno
from players
where sex = ‘F’);

mysql> select playerno, name, town from players where playerno in     (select playerno     from players     where sex = 'F');

实例2（any）：获取至少比同城的另一球员年轻的所有球员的号码，日期和居住城市。

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mysql> select playerno, birth_date, town
from players as p1
where birth_date > any
(select birth_date
from players as p2
where p1.town = p2.town);

mysql> select playerno, birth_date, town from players as p1 where birth_date > any     (select birth_date     from players as p2     where p1.town = p2.town);

实例3（all）：获取最老球员的号码，名字及生日。（即出生日期数值小于或等于所有其它球员的球员）

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mysql> select playerno, name, birth_date
from players
where birth_date <= all
(select birth_date
from players);

mysql> select playerno, name, birth_date from players where birth_date <= all     (select birth_date     from players);

4.7 where型子查询

参考4.4节子查询语句

4.8 from型子查询

参考4.3节子查询语句

4.9 exists型子查询

EXISTS关键字表示存在。使用EXISTS关键字时，内层查询语句不返回查询的记录，而是返回一个真假值，如果内层查询语句查询到满足条件的记录，只要子查询中至少返回一个值，则EXISTS语句的值就为True。就返回true，否则返回false。当返回的值为true时，外层查询语句将进行查询，否则不进行查询。NOT EXISTS刚好与之相反。exists的用法和in ()差不多，但是它们还是有区别的。主要是看两个张表大小差的程度。若子查询表大则用exists（内层索引），子查询表小则用in（外层索引）;

实例1（exists）：获取那些至少支付了一次罚款的球员的名字和首字母。

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mysql> select name, initials
from players
where exists
(select * from penalties
where playerno = players.playerno);

mysql> select name, initials from players where exists     (select * from penalties     where playerno = players.playerno);

实例2（not exists）：获取那些从来没有罚款的球员的名字和首字母。

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mysql> select name, initials
from players
where not exists
(select * from penalties
where playerno = players.playerno);

mysql> select name, initials from players where not exists     (select * from penalties     where playerno = players.playerno);

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原文地址：http://blog.csdn.net/jesseyoung/article/details/40108781
博客主页：http://blog.csdn.net/jesseyoung

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