sql server - How does this SQL syntax work? -


this question has answer here:

i came across horrifyingly freakish sql query today developer generated sql server query designer tool. i hate query designer, i'm stuck trying figure out did. i've never seen syntax before , don't understand it. how work?

in particular is multiple on clauses joined separate join clauses throwing me off.

select *  dbo.tbldealstatus     right outer join dbo.tbluser             right outer join dbo.tblownerlocation                      inner join dbo.tblowner                           inner join dbo.tbldeal                            on dbo.tblowner.ownerid = dbo.tbldeal.ownerid                       on dbo.tblownerlocation.dealid = dbo.tbldeal.dealid              on dbo.tbluser.userid = dbo.tbldeal.chk_contact             left outer join dbo.tblcompany tblcompany_1                     inner join dbo.tblparticipation                      on tblcompany_1.companyid = dbo.tblparticipation.companyid              on dbo.tbldeal.participationid = dbo.tblparticipation.participationid      on /*...       ....so on , forth...*/

first, make rule clarity never mix right , left joins in same query. right joins can switched left joins , alone make easier figure out going on.

next abandon select *. never appropraite in query joins returning same data in 2 or more fields (the join fields) , wasteful of valuable network , database processing time.

i believe wierd ons forcing query go in particular order. bad , should not used in opinion hard maintain , hard developers understand not common , totally unneeded. reversing right joins , putting tables in order need join them may fix this. if not may need few derived tables right data. note in reversing it, may need change inner joins else. right such mess, highly not return correct results. in rewriting it, while want see if changes change results, want use judgement determine if changes fixes bad query or incorrect changes translate query maintainable.

if developer wrote mess still there, force him rewrite in in more standard sql , tell him forbidden ever use query designer again. fails code review far concerned.

if rewriting this, table should first in query , work down there. personal guess right tbldeal table don't know data model wrong.


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