title: MySQL - Skip column in index
body: <p>We have a (big) table with a multiple-column index on columns A, B and C.
  Now we want to do a query with the following format:
   <code>SELECT * FROM table WHERE (B=... AND C=...) OR (B=... AND C=...) OR ...</code>
  Because there are many rows in the table, and no index is used, the performance of the query is very bad.</p>
  
  <p>An index with columns B, C would have been ideal, unfortunately it's not available, and we cannot change it as well (other vendor). Column A has a value where we are not interested in.</p>
  
  <p>To let MySQL use the available index, we have added an extra condition in the WHERE: <code>SELECT * FROM table WHERE (A IN (1, 2, 3, 4, 5, ..., 99, 100)) ((B=... AND C=...) OR (B=... AND C=...))OR ...</code>. The result is that now the index is properly used, and the query performance is already a lot better. However it looks a bit ugly to provide all possible values of A in the query. My feeling is that there should be an easier way to do the same, or with even a better performance.</p>
  
  <p>Is there a way to force MySQL to use the index, even when column A is not used in the query? Or have we already found the best solution?</p>