子查詢，巢狀查詢，nested query，是巢狀在外層查詢where語句中的查詢，子查詢為主查詢返回其所需的資料，或者對外查詢中的查詢結果作進一步限制。
select..
.from
table
where
#主查詢，外層查詢
(select..
from
table
where..
.);#子查詢，內層查詢
select..
.from
table
where col_name 關係運算子 |in|
notin
(select col_name from
table
where..
.);關係運算子：=、<、>、<=、>=、!=
查詢和潘多拉老師在乙個學院的教師資訊
select
*from teacher
where department_id =
(select department_id from teacher where teacher_name=
'潘多拉'
)查詢哪些同學至少有一門功課在95分以上
select student_id,student_name from student where student_id in
(select
distinct student_id from choose where score=95)
;查詢所有成績都在85分以上的同學
select student_id,student_name from student
where student_id notin(
select
distinct student_id from choose where score<
85)
select
from
table
where col_name 關係運算子 [
any|
some
|all](
select col_name from
table
where..
.);
查詢有成績大於等於'201710201102'同學的所有成績的同學資訊
select
distinct a.student_id,a.student_name
from student a inner
join choose b on a.student_id=b.student_id
where b.score>=
all(
select choose.score from choose where choose.student_id=
'201710201102');
select
distinct a.student_id,a.student_name
from student a inner
join choose b on a.student_id=b.student_id
where b.score>=
(select
max(choose.score)
from choose where choose.student_id=
'201710201102'
);
select
from
table
where
[exists
|not
exists](
select col_name from
table
where..
.);
查詢還沒有教師的學院資訊
select
*from department where
department_id notin(
select
distinct department_id from teacher)
;查詢教師表中所有的學院id，然後對比部門表中所有的id，即可得到沒有教師的學院資訊
select
*from department
where
notexists
(select
distinct department_id from teacher where department.department_id=teacher.department_id)
;
在create
table命令中，使用select查詢可以把現有表的結構和資料複製到新錶，但不複製索引。
。只複製結構
create
table newtable [as]
select..
.from..
.limit
0。複製結構和資料
create
table newtable [as]
select..
.from..
.limit
offset
, count
create
table newteacher as
select
*from teacher limit0,
0只複製teacher表的結構到新錶
create
table newdepartment as
select
*from department;
複製department表的結構與資料
create
table student2017 as
select
*from student where
left
(student_id,4)
='2017'
;將學生表中所有2017級的學生資訊複製到新錶
在insert、delete和update語句中使用select查詢，可實現資料的新增、刪除和更新。
❖ insert
into tablea select
from tableb where..
;❖ delete
from
table
where （select子查詢）;
❖ update tablea set fileda =
(select fieldb from tableb where..
.)where……;
insert
into newteacher
select
*from teacher where professional=
'教授'
;將教師表中所有職稱為教授的教師資訊複製到新錶。
update newdepartment set department_name =
'繼續教育學院'
where department_id=
'102'
;修改指定id的部門名稱
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