1.蛙蛙推荐：一些精妙的SQL语句
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 |
