簡單的sql語句(編輯修改稿)
2024-10-20 06:55 本頁面
【文章內(nèi)容簡介】 nme相當(dāng)于做笛卡兒積,如查詢李山的同鄉(xiāng)：select * from students where native in(select native from students where name=’ 李山’),比如，下面兩句是等價的：select * from students where sno in(select sno from grades where o=’B2’)select * from students where exists(select * from grades where = AND o=’B2’)，有兩種方法：asc升序和desc降序,可以按照查詢條件中的某項(xiàng)排列，而且這項(xiàng)可用數(shù)字表示，如：select sno,count(*),avg(mark)from grades group by sno having avg(mark)85 order by 3 ，應(yīng)該用“[]”括住。，如: select sno, courseno from grades where mark IS NULL，any相當(dāng)于邏輯運(yùn)算“||”而all則相當(dāng)于邏輯運(yùn)算“amp。amp?！保喝?，沒有選修‘B2’課程的學(xué)生 ：select students.* from students, grades where = AND ’B2’上面的查詢方式是錯誤的，正確方式見下方：select * from students where not exists(select * from grades where = AND o=39。B239。)：如，選修了全部課程的學(xué)生：select * from students where not exists(select * from courses where NOT EXISTS(select * from grades where sno= AND o=))最外一重：從學(xué)生表中選，排除那些有課沒選的。用not exist。由于討論對象是課程，所以第二重查詢從course表中找，排除那些選了課的即可。第三篇：幾個簡單的基本的sql語句幾個簡單的基本的sql語句(1)數(shù)據(jù)記錄篩選：sql=“select * from 數(shù)據(jù)表 where 字段名=字段值 order by 字段名[desc]”sql=“select * from 數(shù)據(jù)表 where 字段名 like 39。%字段值%39。 order by 字段名 [desc]”sql=“select top 10 * from 數(shù)據(jù)表 where 字段名 order by 字段名[desc]”sql=“select * from 數(shù)據(jù)表 where 字段名 in(39。值139。,39。值239。,39。值339。)”sql=“select * from 數(shù)據(jù)表 where 字段名 between 值1 and 值2”(2)更新數(shù)據(jù)記錄：sql=“update 數(shù)據(jù)表 set 字段名=字段值 where 條件表達(dá)式”sql=“update 數(shù)據(jù)表 set 字段1=值1,字段2=值2 …… 字段n=值n where 條件表達(dá)式”(3
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