目錄

• 插入數(shù)據(jù)
• select子查詢(外語句先執(zhí)行，內(nèi)語句后執(zhí)行)
• 總結(jié)

嵌套查詢又稱子查詢，有select子查詢，where子查詢，from子查詢，exists子查詢。

插入數(shù)據(jù)

#創(chuàng)建表及插入記錄CREATE TABLE class (  cid int(11) NOT NULL AUTO_INCREMENT,  caption varchar(32) NOT NULL,  PRIMARY KEY (cid)) ENGINE=InnoDB CHARSET=utf8; INSERT INTO class VALUES(1, "三年二班"), (2, "三年三班"), (3, "一年二班"), (4, "二年九班"); CREATE TABLE course(  cid int(11) NOT NULL AUTO_INCREMENT,  cname varchar(32) NOT NULL,  teacher_id int(11) NOT NULL,  PRIMARY KEY (cid),  KEY fk_course_teacher (teacher_id),  CONSTRAINT fk_course_teacher FOREIGN KEY (teacher_id) REFERENCES teacher (tid)) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO course VALUES(1, "生物", 1), (2, "物理", 2), (3, "體育", 3), (4, "美術(shù)", 2); CREATE TABLE score (  sid int(11) NOT NULL AUTO_INCREMENT,  student_id int(11) NOT NULL,  course_id int(11) NOT NULL,  num int(11) NOT NULL,  PRIMARY KEY (sid),  KEY fk_score_student (student_id),  KEY fk_score_course (course_id),  CONSTRAINT fk_score_course FOREIGN KEY (course_id) REFERENCES course (cid),  CONSTRAINT fk_score_student FOREIGN KEY (student_id) REFERENCES student(sid)) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO score VALUES(1, 1, 1, 10),(2, 1, 2, 9),(5, 1, 4, 66),(6, 2, 1, 8),(8, 2, 3, 68),(9, 2, 4, 99),(10, 3, 1, 77),(11, 3, 2, 66),(12, 3, 3, 87),(13, 3, 4, 99),(14, 4, 1, 79),(15, 4, 2, 11),(16, 4, 3, 67),(17, 4, 4, 100),(18, 5, 1, 79),(19, 5, 2, 11),(20, 5, 3, 67),(21, 5, 4, 100),(22, 6, 1, 9),(23, 6, 2, 100),(24, 6, 3, 67),(25, 6, 4, 100),(26, 7, 1, 9),(27, 7, 2, 100),(28, 7, 3, 67),(29, 7, 4, 88),(30, 8, 1, 9),(31, 8, 2, 100),(32, 8, 3, 67),(33, 8, 4, 88),(34, 9, 1, 91),(35, 9, 2, 88),(36, 9, 3, 67),(37, 9, 4, 22),(38, 10, 1, 90),(39, 10, 2, 77),(40, 10, 3, 43),(41, 10, 4, 87),(42, 11, 1, 90),(43, 11, 2, 77),(44, 11, 3, 43),(45, 11, 4, 87),(46, 12, 1, 90),(47, 12, 2, 77),(48, 12, 3, 43),(49, 12, 4, 87),(52, 13, 3, 87);  CREATE TABLE student(  sid int(11) NOT NULL AUTO_INCREMENT,  gender char(1) NOT NULL,  class_id int(11) NOT NULL,  sname varchar(32) NOT NULL,  PRIMARY KEY (sid),  KEY fk_class (class_id),  CONSTRAINT fk_class FOREIGN KEY (class_id) REFERENCES class (cid)) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO student VALUES(1, "男", 1, "理解"), (2, "女", 1, "鋼蛋"), (3, "男", 1, "張三"), (4, "男", 1, "張一"), (5, "女", 1, "張二"), (6, "男", 1, "張四"), (7, "女", 2, "鐵錘"), (8, "男", 2, "李三"), (9, "男", 2, "李一"), (10, "女", 2, "李二"), (11, "男", 2, "李四"), (12, "女", 3, "如花"), (13, "男", 3, "劉三"), (14, "男", 3, "劉一"), (15, "女", 3, "劉二"), (16, "男", 3, "劉四") CREATE TABLE teacher(  tid int(11) NOT NULL AUTO_INCREMENT,  tname varchar(32) NOT NULL,  PRIMARY KEY (tid)) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO teacher VALUES(1, "張磊老師"), (2, "李平老師"), (3, "劉海燕老師"), (4, "朱云海老師"), (5, "李杰老師");

select子查詢(外語句先執(zhí)行，內(nèi)語句后執(zhí)行)

例1. 查詢課程名并顯示課程老師的名稱

?select * from course c where c.teacher_id="1"; select * from teacher t where t.tid="1"; ??-- 最后拼接select * ,(select tname from teacher t where t.tid=c.teacher_id)name from course c;

where 子查詢（先執(zhí)行子查詢，再執(zhí)行外查詢）

例2.查詢學(xué)習(xí)了體育的學(xué)生

-- 選擇了體育學(xué)生的idselect sc.student_id from course co left join score sc on co.cid=sc.course_id where cname="體育"-- 通過學(xué)生表用學(xué)生id匹配學(xué)生姓名select st.sname from student st where st.sid in(select sc.student_id from course co left join score sc on co.cid=sc.course_id where cname="體育")

部分結(jié)果：

from 子查詢(先執(zhí)行子查詢，再執(zhí)行外查詢)

例3.列出三年二班學(xué)了體育的學(xué)生

select a.* from (select st.sname,cl.caption from score sc left join course co on sc.course_id=co.cidleft join student st on st.sid=sc.student_idleft join class cl on cl.cid=st.class_idwhere co.cname="體育")a where a.caption="三年二班";

exists 子查詢

(先執(zhí)行外語句，再執(zhí)行子查詢，根據(jù)子查詢返回結(jié)果判斷是否保留外查詢結(jié)果)

例4.查詢學(xué)了課程di為1的學(xué)生的姓名

select * from student st where exists(select *from score sc where course_id="1" and sc.student_id=st.sid);

總結(jié)

sql查詢本質(zhì)就是對各種表進行裁剪和拼接，最后得到我們想要的數(shù)據(jù)。

所有的能通過子查詢完成的查詢都能用連接查詢完成，如例1：查詢課程名并顯示課程老師的名稱

select *from course coleft join teacher te on te.tid=co.teacher_id;

所以要靈活運用查詢方式，才能更高效的查詢。

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