| 经典的SQL语句 |
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说明：复制表(只复制结构,源表名：a 新表名：b)
SQL: select * into b from a where 1＜＞1
说明：拷贝表(拷贝数据,源表名：a 目标表名：b)
SQL: insert into b(a, b, c) select d,e,f from b;
说明：显示文章、提交人和最后回复时间
SQL: select a.title,a.username,b.adddate from table a,(select max(adddate) adddate from table where table.title=a.title) b
说明：外连接查询(表名1：a 表名2：b)
SQL: select a.a, a.b, a.c, b.c, b.d, b.f from a LEFT OUT JOIN b ON a.a = b.c
说明：日程安排提前五分钟提醒
SQL: select * from 日程安排 where datediff(''minute'',f开始时间,getdate())＞5
说明：两张关联表，删除主表中已经在副表中没有的信息
SQL:
delete from info where not exists ( select * from infobz where info.infid=infobz.infid )
说明：--
SQL:
SELECT A.NUM, A.NAME, B.UPD_DATE, B.PREV_UPD_DATE
FROM TABLE1,
(SELECT X.NUM, X.UPD_DATE, Y.UPD_DATE PREV_UPD_DATE
FROM (SELECT NUM, UPD_DATE, INBOUND_QTY, STOCK_ONHAND
FROM TABLE2
WHERE TO_CHAR(UPD_DATE,''YYYY/MM'') = TO_CHAR(SYSDATE, ''YYYY/MM'')) X,
(SELECT NUM, UPD_DATE, STOCK_ONHAND
FROM TABLE2
WHERE TO_CHAR(UPD_DATE,''YYYY/MM'') =
TO_CHAR(TO_DATE(TO_CHAR(SYSDATE, ''YYYY/MM'') ''/01'',''YYYY/MM/DD'') - 1, ''YYYY/MM'') ) Y,
WHERE X.NUM = Y.NUM （+）
AND X.INBOUND_QTY + NVL(Y.STOCK_ONHAND,0) ＜＞ X.STOCK_ONHAND ) B
WHERE A.NUM = B.NUM
说明：--
SQL:
select * from studentinfo where not exists(select * from student where studentinfo.id=student.id) and 系名称=''"&strdepartmentname&"'' and 专业名称=''"&strprofessionname&"'' order by 性别,生源地,高考总成绩
说明：
从数据库中去一年的各单位电话费统计(电话费定额贺电化肥清单两个表来源）
SQL:
SELECT a.userper, a.tel, a.standfee, TO_CHAR(a.telfeedate, ''yyyy'') AS telyear,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''01'', a.factration)) AS JAN,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''02'', a.factration)) AS FRI,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''03'', a.factration)) AS MAR,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''04'', a.factration)) AS APR,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''05'', a.factration)) AS MAY,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''06'', a.factration)) AS JUE,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''07'', a.factration)) AS JUL,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''08'', a.factration)) AS AGU,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''09'', a.factration)) AS SEP,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''10'', a.factration)) AS OCT,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''11'', a.factration)) AS NOV,
SUM(decode(TO_CHAR(a.telfeedate, ''mm''), ''12'', a.factration)) AS DEC
FROM (SELECT a.userper, a.tel, a.standfee, b.telfeedate, b.factration
FROM TELFEESTAND a, TELFEE b
WHERE a.tel = b.telfax) a
GROUP BY a.userper, a.tel, a.standfee, TO_CHAR(a.telfeedate, ''yyyy'')
说明：四表联查问题：
SQL: select * from a left inner join b on a.a=b.b right inner join c on a.a=c.c inner join d on a.a=d.d where .....
说明：得到表中最小的未使用的ID号
SQL:
SELECT (CASE WHEN EXISTS(SELECT * FROM Handle b WHERE b.HandleID = 1) THEN MIN(HandleID) + 1 ELSE 1 END) as HandleID
FROM Handle
WHERE NOT HandleID IN (SELECT a.HandleID - 1 FROM Handle a)
2.删除重复数据
一、具有主键的情况
a.具有唯一性的字段id(为唯一主键)
delete table
where id not in
(
select max(id) from table group by col1,col2,col3...
)
group by 子句后跟的字段就是你用来判断重复的条件，如只有col1，那么只要col1字段内容相同即表示记录相同。
b.具有联合主键
假设col1+'',''+col2+'',''...col5 为联合主键
select * from table where col1+'',''+col2+'',''...col5 in (
select max(col1+'',''+col2+'',''...col5) from table
where having count(*)＞1
group by col1,col2,col3,col4
)
group by 子句后跟的字段就是你用来判断重复的条件，如只有col1，那么只要col1字段内容相同即表示记录相同。
c:判断所有的字段
select * into #aa from table group by id1,id2,....
delete table
insert into table
select * from #aa
二、没有主键的情况
a:用临时表实现
select identity(int,1,1) as id,* into #temp from ta
delete #temp
where id not in
(
select max(id) from # group by col1,col2,col3...
)
delete table ta
inset into ta(...)
select ..... from #temp
b:用改变表结构（加一个唯一字段）来实现
alter table 表 add newfield int identity(1,1)
delete 表
where newfield not in
(
select min(newfield) from 表 group by 除newfield外的所有字段
)
alter table 表 drop column newfield
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