基本SQL小结
上一篇 / 下一篇 2007-07-12 22:58:05 / 个人分类:数据库
YU{~E8?K0今天对SQL的基础知识做个小结:
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K lI0r(|%d E*Mj.s01,select [select_list]
E8C4Vmi0#KwpJ2aM7x;W4@0 from [table_name]
h E!CJJ3K)q-D-B051Testing软件测试网_^6n2zV3o$N$kwhere [search_conditions]51Testing软件测试网-\V G7b;z|"]
)V/df9G'\h w oj0 group by [group_by_list]51Testing软件测试网 \C4Xq({HH
P k_0[G+E},x0 (having [search_conditions])
v{3R-YZJF~b051Testing软件测试网8Y3\l!C"EEXorder by [order_list]
+TpM3k[00l m%m(c3~0 (compute [function])
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51Testing软件测试网'abp6n7mwhere子句的查询条件可以包括:51Testing软件测试网S~^e~_V7`
51Testing软件测试网4k4LpDq0VB比较运算符:<,>,<=,>=,=,!=,!<,!>
'L9~Mj,])`pqj051Testing软件测试网4O;Q0B[2PB范围说明:between A and b, not between A and b51Testing软件测试网V*w1lVfG-c/uc0q+g
s)s Q-vJKG0可选值列表:in( ), not in()51Testing软件测试网r?"Fx+l&t*v7m
51Testing软件测试网%H#W1k4xx模式匹配:like '_', not like'%'51Testing软件测试网Ber5w._#^TC+^k
7\9`{+]:V0是否为空值:is null, is not null51Testing软件测试网9V)o6N L1\:w;i*sec
+f&`#GW)d4[~2ui|0逻辑组合:and, or, not51Testing软件测试网i-X/g0H;eQ
*Z1I)JZEA0b.group by
-l8` \/hr~8jol0m)^9NR)M3uGx0 根据条件自动分组,上下分开。
^9u8^#Ku:R B'Qq/_051Testing软件测试网N}/t/{:^W0Ehaving子句,和group by连用,对分组指定搜索条件。
.A/@{7qF}{051Testing软件测试网(e8c2@,mq uYeg.查询多个员工的工资不低于6000的部门编号。51Testing软件测试网5a8G.B'l"Of(Wp;b
2XI6y7\y9R ]:E~\0 select dept_id,count(*)from employee
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51Testing软件测试网:RL$I,tA `&C%N3Z Ogroup by dept_id
5p{1Y8S W051Testing软件测试网)N `}2t@@*{having count(*)>=1(多个)
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51Testing软件测试网 GO^ S|(ECrd.function 汇总函数(针对行)|(针对列)字段之间直接进行数学计算
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,a'CIAi0Em)m|051Testing软件测试网 V zw6U|"T.[Y(tlcount([*]统计元组个数,[列名]统计一列中值的个数)
*`7x(Z;|+i{0k+^P06JO I9[7g+\QD0e.union(行连接)
eI-e]K051Testing软件测试网,~T vx:^5g将两个或两个以上的查询结果合并为一个结果集。
-zeg#Pf:PA3m0ce7[x%jl1F0eg.查询计算机系的学生或者年龄不大于20的学生,按年龄倒序。
5o n0_]az;Qe~*ds0M.PCk `7w0FJ0select * from department where sdept='计算机'51Testing软件测试网(t{DQ^'}%q-z
51Testing软件测试网(`z}8d8q5NQvd'pLunion
9`)S.e-y*u5VI O051Testing软件测试网X*N+A3u0K s~4Ipselect * from student where sage<=2051Testing软件测试网4w a8e*o7~mQ"o
51Testing软件测试网W1v:t:x[YU1Y-dorder by sage desc51Testing软件测试网9A[T;i~n;X
51Testing软件测试网1l_.|^YO]gf.嵌套51Testing软件测试网(Sd#r:q~ Q7U"W)s
51Testing软件测试网ke FMq,TQ7Ceg1.查出与学号9500同龄的学生。