SQL Server query execution very slow when comparing Primary Keys -


i have sql server 2008 r2 database table 12k address records trying filter out duplicate phone numbers , flag them using following query

select a1.id, a2.id     addresses a1      inner join  addresses a2 on a1.phonenumber = a2.phonenumber   a1.id < a2.id

note: realize there way solve problem using exists, not part of discussion.

the table has primary key on id field clustered index, fragmentation level 0 , phone number field not null , has 130 duplicates out of 12k records. make sure not server or database instance issue ran on 4 different systems.

execution of query takes several minutes, several hours. after trying 1 of last steps removed primary key , ran query without , voila executed in under 1 second. added primary key , still ran in under 1 second.

does have idea causing problem?

is possible primary key gets somehow corrupted?

edit: apologies had couple of typos in sql query

out of data statistics. dropping , recreating pk give fresh statistics.

too late now, i'd have suggest running sp_updatestats see happened.

if backup , restore database onto different systems, statistics follow data

i'd suspect different plan after non-indexed (i guess) columns phonenumber , ccaphonen


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