return row only if value not in other row

Have the following subset of tblMember:

mem_num     product_type         address
1                          A                      main st
1                          C                      main st                      
2                          A                      1st street
2                          C                      1st street
2                          D                      1st street
3                          A                      2nd street
3                          B                      2nd street
4                          A                      3rd street
4                          C                      3rd street

I want to select only rows with product_type 'A', if mem_num does not have product type 'B' in another row or

mem_num       product_type         address
1                          A                         main
2                          A                         1st Street
4                          A                         3rdStreet

Thanks!
needpleaseAsked:
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Dan CraciunConnect With a Mentor IT ConsultantCommented:
SELECT * FROM tblMember 
    WHERE product_type='A' AND mem_num NOT IN (
    SELECT mem_num FROM tblMember WHERE product_type='B'
)

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HTH,
Dan
0
 
Guy Hengel [angelIII / a3]Connect With a Mentor Billing EngineerCommented:
I prefer for this kind of queries the NOT EXISTS syntax, especially if the number of rows having the product_type='B' here to be huge
SELECT m.*
  FROM tblMember  m
    WHERE m.product_type='A' 
AND NOT EXISTS( 
    SELECT null 
   FROM tblMember o
   WHERE o.product_type='B'
       and o.mem_num  = m.mem_num 
) 

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you shall have a (single) index on the columns mem_num + product_type to ensure the query runs as fast as possible
0
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