作爲一枚Java後端開發者，數據庫知識必不可少，對數據庫的掌握熟悉度的考察也是對這個人是否有紮實基本功的考察。特別對於初級開發者，面試可能不會去問框架相關知識，但是絕對不會不去考察數據庫知識，這裏收集一些常見類型的SQL語句，無論對於平常開發還是準備面試，都會有助益。
基本表結構：
student(sno,sname,sage,ssex)學生表
course(cno,cname,tno) 課程表
sc(sno,cno,score) 成績表
teacher(tno,tname) 教師表
101，查詢課程1的成績比課程2的成績高的所有學生的學號
select a.sno from
(select sno,score from sc where cno=1) a,
(select sno,score from sc where cno=2) b
where a.score>b.score and a.sno=b.sno
102，查詢平均成績大於60分的同學的學號和平均成績
select
a.sno as "學號", avg(a.score)
as "平均成績"
from
(select sno,score from sc) a
group by sno having avg(a.score)>60
103，查詢所有同學的學號、姓名、選課數、總成績
select
a.sno as 學號, b.sname as 姓名,
count(a.cno) as 選課數, sum(a.score)
as 總成績
from sc a, student b
where a.sno = b.sno
group by a.sno, b.sname
或者：
selectstudent.sno
as 學號, student.sname as 姓名,
count(sc.cno) as 選課數, sum(score)
as 總成績
from student left Outer join sc on student.sno = sc.sno
group by student.sno, sname
104，查詢姓“張”的老師的個數
selectcount(distinct(tname))
from teacher where tname like '張%‘
或者：
select tname
as "姓名",
count(distinct(tname)) as "人數"
from teacher
where tname like'張%'
group by tname
105，查詢沒學過“張三”老師課的同學的學號、姓名
select student.sno,student.sname from student
where sno not in (select distinct(sc.sno) from sc,course,teacher
where sc.cno=course.cno and teacher.tno=course.tno and teacher.tname='張三')
106，查詢同時學過課程1和課程2的同學的學號、姓名
select sno, sname from student
where sno in (select sno from sc where sc.cno = 1)
and sno in (select sno from sc where sc.cno = 2)
或者：
selectc.sno, c.sname from
(select sno from sc where sc.cno = 1) a,
(select sno from sc where sc.cno = 2) b,
student c
where a.sno = b.sno and a.sno = c.sno
或者：
select student.sno,student.sname from student,sc where student.sno=sc.sno and sc.cno=1
and exists( select * from sc as sc_2 where sc_2.sno=sc.sno and sc_2.cno=2)
107，查詢學過“李四”老師所教所有課程的所有同學的學號、姓名
select a.sno, a.sname from student a, sc b
where a.sno = b.sno and b.cno in
(select c.cno from course c, teacher d where c.tno = d.tno and d.tname = '李四')
或者：
select
a.sno, a.sname from student a, sc b,
(select c.cno from course c, teacher d where c.tno = d.tno and d.tname = '李四') e
where a.sno = b.sno and b.cno = e.cno
108，查詢課程編號1的成績比課程編號2的成績高的所有同學的學號、姓名
select a.sno, a.sname from student a,
(select sno, score from sc where cno = 1) b,
(select sno, score from sc where cno = 2) c
where b.score > c.score and b.sno = c.sno and a.sno = b.sno
109，查詢所有課程成績小於60分的同學的學號、姓名
select sno,sname from student
where sno not in (select distinct sno from sc where score > 60)
110，查詢至少有一門課程與學號爲1的同學所學課程相同的同學的學號和姓名
select distinct a.sno, a.sname
from student a, sc b
where a.sno <> 1 and a.sno=b.sno and
b.cno in (select cno from sc where sno = 1)
或者：
select s.sno,s.sname
from student s,
(select sc.sno
from sc
where sc.cno in (select sc1.cno from sc sc1 where sc1.sno=1)and sc.sno<>1
group by sc.sno)r1
where r1.sno=s.sno