Those notorious SQL

Source: Internet
Author: User

    • Two or more tables are associated, not written in the where condition, a large number of Cartesian values, which can cause problems in the database.
Select *  from  Left Join  on =  Left Join  on =
    • Multiple Table association queries, where conditions use a variety of functions, resulting in an invalid index. The amount of data that will cause the query to look like a snail after hitting it.
SelectTrim (D.circuitid) asCircuitid,trim (D.code) asCode,trim (d.oldname) asOldname,trim (D.circuittype) asCircuittype,trim (d.status) asStatus,trim (D.customerid) asAcustomerid,trim (D.alinkman) asAlinkman,trim (D.zlinkman) asZlinkman,trim (D.alinkmantel) asAlinkmantel,trim (D.zlinkmantel) asZlinkmantel,trim (d.busi_no) asBusi_no,trim (d.service_serial) asService_serial,trim (a.region_id) asRegionID,2  asSORTID fromtest1 a,test2 b,test3 c,test4 DwhereTrim (a.room_id)=Trim (B.roomid) andTrim (B.neid)=Trim (C.neid) and(Trim (C.portid)=Trim (d.aendname)orTrim (C.portid)=Trim (d.zendname))

Those notorious SQL

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