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  1. #1
    SitePoint Addict lmasi02's Avatar
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    Derived query from a Union

    Hi All,

    How can i write a query to count the number of records from a derived table. the derived table is a union of two table.

    select msisdn from enrollOffer union DISTINCT select msisdn from enrollHistory
    Power of Knowledge

  2. #2
    From Italy with love silver trophybronze trophy
    guido2004's Avatar
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    Code:
    SELECT COUNT(*)
    FROM 
      (SELECT
         msisdn 
       FROM enrollOffer 
       UNION 
       SELECT 
         msisdn 
       FROM enrollHistory
      )
    If you want to count msisdn that are present in both tables as well, use UNION ALL.

  3. #3
    SitePoint Addict lmasi02's Avatar
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    Quote Originally Posted by guido2004 View Post
    Code:
    SELECT COUNT(*)
    FROM 
      (SELECT
         msisdn 
       FROM enrollOffer 
       UNION 
       SELECT 
         msisdn 
       FROM enrollHistory
      )
    If you want to count msisdn that are present in both tables as well, use UNION ALL.
    I tried this and am getting the error
    ERROR 1248 (42000): Every derived table must have its own alias
    Power of Knowledge

  4. #4
    From Italy with love silver trophybronze trophy
    guido2004's Avatar
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    Code:
    SELECT COUNT(*)
    FROM 
      (SELECT
         msisdn 
       FROM enrollOffer 
       UNION 
       SELECT 
         msisdn 
       FROM enrollHistory
      ) AS a
    Ah yes, forgot the alias

  5. #5
    SitePoint Addict lmasi02's Avatar
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    I have tried to put the alian as
    SELECT COUNT(cout) FROM (SELECT msisdn as cout FROM enrollOffer UNION SELECT msisdn as cout FROM enrollHistory );
    but it is all failing. same error message
    Power of Knowledge

  6. #6
    SQL Consultant gold trophysilver trophybronze trophy
    r937's Avatar
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    have a look at exactly where guido put the alias -- compare post #2 and post #4
    rudy.ca | @rudydotca
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