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Karander
Starting Member
34 Posts |
 Posted - 2006-10-01 : 11:44:32
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| Hi, I have several questions which concern bulding fast sql query ...1) If i haev several tables. I join them 6 - times, these tables are very huge, mln records each. What is the best approach to query them. I know this is a general question, but I would like to know what is best method to start writing query, what should i take a note of sth for ?2) I have thought, that if I limit records from one table and then i will join this table to rest of them, i will have better efficiency .. and i wrote sth like this: select sth from table1 join table2 on .. join table3 on .. join (select sth2 S from table where S = PARAM ) S on .... where ... and theoretically this query is executed fast, but the problem was when i wanted to place this select in external update select .. and write sth liks this: update T set field1 = ( select sth from table1 join table2 on .. join table3 on .. join (select sth2 S from table where S = T.PARAM ) S on .... where ... ) from table T and the problem is that mssql doesn't see T.PARAM and probable there is not workaround. Anyway I have constructed this query joining subquery to have more efficiency... how could i this update query subsititute for another working one ...3. what is different in performance between joing tables or writing subqueries4. Any tutorial, article, query building will be very appreciatedThanks :) |
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Page47
Master Smack Fu Yak Hacker
2878 Posts |
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Building queries ...