一些记录查询的SQL语句

-- ======================== 第三天 ===========================
CREATE DATABASE php0408 CHARSET utf8
;CREATE TABLE php0408.student (
	sid INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
	sname VARCHAR(18) NOT NULL,
	sex ENUM('male','female') NOT NULL DEFAULT 'female',
	cid INT UNSIGNED NOT NULL
) ENGINE=MYISAM

;CREATE TABLE php0408.class (
    id INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
    cname VARCHAR(10) NOT NULL
) ENGINE=MYISAM

;USE php0408
;SHOW TABLES

;INSERT INTO php0408.`class` VALUES(NULL,'php0306'),(NULL,'php0420'),(NULL,'php1101')
;SELECT * FROM php0408.`class`
;INSERT INTO student VALUES(NULL,'小花',1,8)
;SELECT * FROM student

;DROP TABLE student
;DROP TABLE class
;CREATE TABLE php0408.student (
	sid INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
	sname VARCHAR(18) NOT NULL,
	sex ENUM('male','female') NOT NULL DEFAULT 'female',
	cid INT UNSIGNED NOT NULL,
	CONSTRAINT FOREIGN KEY (cid) REFERENCES class(id) ON DELETE RESTRICT ON UPDATE CASCADE
) ENGINE=INNODB
;CREATE TABLE php0408.class (
    id INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
    cname VARCHAR(10) NOT NULL
) ENGINE=INNODB
;SHOW CREATE TABLE student
#创建外键
;ALTER TABLE student ADD CONSTRAINT `student_cid_class_id` FOREIGN KEY (cid) REFERENCES class(id)
#删除外键，要使用外键的名字
;ALTER TABLE student DROP FOREIGN KEY `student_cid_class_id`

;SELECT * FROM student
;UPDATE student SET cid=1 WHERE sid=1
;SELECT * FROM class
# 附表创建记录时，必须保证外键字段数据在主表中存在
;INSERT INTO student VALUES(NULL,'小芳',2,8)
# 删除主表主键的时候，会检查外键约束，如果别的表依赖该记录，则不能删除
;DELETE FROM class WHERE id=1

#可以设置主表记录发生变化的时候，关联表做什么操作：比如修改主表记录，关联表相应修改，删除主表记录，关联表置空
;ALTER TABLE student ADD CONSTRAINT `student_cid_class_id` FOREIGN KEY (cid) REFERENCES class(id) ON DELETE SET NULL ON UPDATE CASCADE
;UPDATE class SET id=0 WHERE id=1
;DELETE FROM class WHERE id=0

;CREATE TABLE nf1(
	NAME CHAR(18),
	sex CHAR(1),
	class CHAR(10),
	room CHAR(10),
	days INT,
	dksj CHAR(20)
)
;DESC nf1
;ALTER TABLE nf1 CHANGE COLUMN dksj `start` DATETIME
;ALTER TABLE nf1 ADD COLUMN `end` DATETIME

;INSERT INTO nf1 VALUES('四哥','男','php0408','603',20,'2015-04-08','2015-05-08')
;SELECT * FROM nf1
;CREATE TABLE nf2(
	NAME CHAR(18),
	sex CHAR(1),
	class CHAR(10),
	room CHAR(10),
	days INT,
	START DATETIME,
	END DATETIME,
	PRIMARY KEY (NAME,class)
)
#补充timestamp知识
;CREATE TABLE php0408.tm(
	c1 TIMESTAMP DEFAULT '2015-05-06 10:00:00',
	c2 TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
)

;INSERT INTO php0408.`tm` (c2) VALUES (NULL)
;SELECT * FROM tm
;UPDATE tm SET c3 =1 WHERE c3 IS NULL
# 插入时出现主键约束
;INSERT INTO student VALUES(1,'小花',2,2)
;SELECT * FROM student
#当插入的数据出现主键冲突时，设定该记录的数据
;INSERT INTO student VALUES(1,'小花',2,2) ON DUPLICATE KEY UPDATE sname='小王'
;CREATE TABLE stu (
	sname VARCHAR(18),
	cid INT UNSIGNED
)
;SELECT * FROM stu
#将其它表中的数据插入到当前表
;INSERT INTO stu SELECT sname,cid FROM student WHERE sid<2

;SELECT 1
;SELECT NOW()
;SELECT CURRENT_TIMESTAMP
#给要展示的字段加一个别名
;SELECT sname AS `姓名` FROM php0408.student
#as也可以省略
;SELECT sname `姓名` FROM php0408.student
;SELECT 1+1 AS rst
;SELECT RAND()

;SELECT * FROM student
;SELECT * FROM class
;SELECT * FROM student,class,tm

#由于两张表中都有sname和cid字段，所以
#为了确定sname来源于student表cid来源于stu表，需要使用表名.字段名的形式
;SELECT student.sname,stu.`cid` FROM student,stu

#给表起别名
;SELECT t1.sex,t1.sname,t2.`cid` FROM student AS t1,stu AS t2

#要求从两张表中取出各自的sname,为了在php中避免键名一样，数组元素覆盖，要给字段起别名
;SELECT t1.sname AS sname1,t2.sname AS sname2 FROM student AS t1,stu AS t2

#有时候为了使sql语句看起来完整，会使用表作为数据来源，但是有些数据无需表的参与，就是用dual虚拟表
;SELECT 1,NOW() FROM DUAL

#where 从 from 所指定的数据来源中，对每条记录进行一次判断，利用条件表达式！
;SELECT * FROM student WHERE FALSE

;SELECT * FROM class WHERE id <>2
#带有php的
;SELECT * FROM class WHERE cname LIKE '%php%'
#带有11的
;SELECT * FROM class WHERE cname LIKE '%11%'
#查询所有以java开头的
;SELECT * FROM class WHERE cname LIKE 'java%'

#列出id是1 或 2 或 3的记录
;SELECT * FROM class WHERE id IN (1,2,3)
#列出id不是1 2 3的记录
;SELECT * FROM class WHERE id NOT IN (1,2,3)

#列出id在2和3之间的，闭合区间
;SELECT * FROM class WHERE id BETWEEN 2 AND 3

# 列出时间在2015/04/30 10:00:00到2015-5-8 0:0:0之间的记录
;SELECT * FROM tm WHERE c1 BETWEEN '2015/04/30 10:00:00' AND '2015-5-8'

;SELECT NULL-0,NULL+0,NULL,NULL*0,NULL+1,NULL=1,NULL=NULL

;CREATE TABLE php0408.nul(
	c1 INT NULL,
	c2 CHAR(8) NULL
)
;INSERT INTO php0408.`nul` VALUES(1,NULL),(2,'2'),(3,3)

#由于null和任何数据进行运算都是null，转换为布尔值结果是false
#所以为了列出字段为null的记录，必须使用is null
;SELECT * FROM nul WHERE c2 IS NULL

#以下两条是相同的
;SELECT * FROM nul WHERE c2 IS NOT NULL
;SELECT * FROM nul WHERE NOT c2 IS NULL

#取出所有的c1为1并且c2为2的记录
;SELECT * FROM nul WHERE c1=1 AND c2=2

#取出所有的c1为1或者c2为2的记录
;SELECT * FROM nul WHERE c1=1 OR c2=2

#运算符优先级,可以使用()提升优先级
;SELECT * FROM nul WHERE c1=1 AND (c2=2 OR c1=3)

#使用group by进行分组
;SELECT *,COUNT(*) FROM stu GROUP BY cid
#如果count里面是一个具体的字段，将会过滤该字段为null的记录
;SELECT *,COUNT(c2) FROM nul GROUP BY c1

#将每一个组里面的cid字段求和展示出来
;SELECT *,COUNT(cid),SUM(cid) FROM stu GROUP BY cid

#取出某个字段最大值
;SELECT *,MAX(sid) FROM student GROUP BY cid
#取出某个字段最小值
;SELECT *,MIN(sid) FROM student

;SELECT *,MAX(sid) FROM student
;SELECT *,AVG(sid) FROM student GROUP BY cid
#将分组后每个记录的姓名 学号展示出来
;SELECT *,GROUP_CONCAT(sname,'-',sid) FROM student GROUP BY cid

#可以在分组后使用排序，asc和desc（降序）
;SELECT cid,COUNT(*) FROM student GROUP BY cid DESC

#根据两个字段进行分组，并且对结果集先按照cid降序排，接着如果cid相同，按照性别升序排
;SELECT cid,COUNT(*),sex FROM student GROUP BY cid DESC,sex ASC

;SELECT cid,COUNT(*) FROM student GROUP BY cid WITH ROLLUP

;SELECT cid,COUNT(*),sex FROM student GROUP BY cid DESC,sex ASC WITH ROLLUP

#求出班级人数超过2个的班级
;SELECT cid,COUNT(*) AS num FROM student GROUP BY cid HAVING num>2

#排序,先按照班级号升序，再按照学号降序
;SELECT * FROM student ORDER BY cid ASC,sid DESC
#随机排
;SELECT *  FROM student ORDER BY RAND()

#limit用于从结果集中取得几条数据,limit受前面子句的影响
;SELECT * FROM student WHERE sid<4 LIMIT 5,2