2.1 创建测试表

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));

2.2 插入测试数据

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');

3 实例分析

3.1 实例1

获取拥有一个联盟会员号码的每个球员的号码和联盟会员的号码。

select playerno, leaguenofrom playerswhere leagueno is not null;

注意：is null不能用=号代替。

mysql> SELECT IFNULL(1,'test');  +------------------+| IFNULL(1,'test') |+------------------+| 1                |+------------------+

由于 expr1 是 1，不为 NULL，所以函数返回1.

mysql> SELECT IFNULL(1/0,'test');+--------------------+| IFNULL(1/0,'test') |+--------------------+| test               |+--------------------+

由于 expr1 是NULL，所以函数返回test.

4 一些注意事项

4.1 排序时mysql将null作为最小值处理。

4.2 not null字段不能插入null，但可以插入空值。

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原文地址：
http://blog.csdn.net/jesseyoung/article/details/40188125

博客主页：
http://blog.csdn.net/jesseyoung

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