在其它网站看到的，感觉值得推荐：
精妙SQL语句 值得推敲
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) 数据库里有多条同名记录。读取出来的时候，相同的就显示一条的方法： select distinct `field` from table field就唯一不会重复了选出出现频率最大的值，例如 CELL_ID DATE TIME BUSY_TCH_MEAN 30151 2003-12-20 0:00:00 0.01 30151 2003-12-20 1:00:00 1.89 30151 2003-12-20 2:00:00 0.59 30151 2003-12-20 3:00:00 0.43 30151 2003-12-20 4:00:00 0.7 30151 2003-12-20 5:00:00 0.01 30151 2003-12-20 6:00:00 0.08 30151 2003-12-20 7:00:00 0.01 30151 2003-12-20 8:00:00 1.2 30151 2003-12-20 9:00:00 1.57 30151 2003-12-20 10:00:00 3.96 30151 2003-12-20 11:00:00 3.96 30151 2003-12-20 12:00:00 5.65 其中BUSY_TCH_MEAN字段出现频率最多的值是0.01，怎么把他找出来（用SQL）？ SELECT `BUSY_TCH_MEAN` , COUNT(*) AS num FROM mytable GROUP BY `BUSY_TCH_MEAN` ORDER BY num DESC LIMIT 0,1
