title: Ignore a column while doing MINUS in SQL query
body: <p>I have written the query:</p>
  <pre><code>Select distinct a,b from t1 minus Select distinct a,b from t2.
  </code></pre>
  <p>Here t1 and t2 are two tables. I want distinct values of a and b that occur in t1 but not in t2. So I'm using minus operator. I want values of both a and b but I know that in some cases the value of b in t1 and t2 maybe different. This would result in values of a and b that are present in both t1 and t2 as minus would not happen if values of b do not match in both the tables. How can I do this successfully?</p>
  <p>How can I get values of a and b that are present in table t1 but not in table t2 even though in some cases values of b might not match in both the tables?</p>
  <pre><code>    table1:                              table2:
  column1  column2                    column1   column2
    1      a                             1         c
    2      b                             3         d
  </code></pre>
  <p>In this case I would want values (2,b) only. I would not want (1,a) as 1 is also present in table2.</p>