基于复杂条件的SQL

Question

I'm struggling with SQL statement that I'm trying to write in MS Access and would appreciate any help.

I have a table:

 ***************************
 * attr1 * attr2 *  attr3  *
 ***************************
 *       *  A    *   1     *
 *       *  B    *   2     *
 *       *  B    *   3     *
 *       *  C    *   4     *
 *   B   *       *   1     *
 *   D   *       *   1     *
 *   A   *       *   2     *
 ***************************

I need result like this:

 ***************************
 * attr1 * attr2 *  attr3  *
 ***************************
 *   B   *       *   1     *
 *   D   *       *   1     *
 *   A   *       *   2     *
 *       *  B    *   3     *
 *       *  C    *   4     *
 ***************************

So, I need in my result all rows where attr1 is not null, and all other rows where attr3 has different values from those in rows where attr1 is not null.

I can do it in Access in a way to make one query where I select all rows where attr1 is not null, than one "find unmatched" query where I select all rows with values in attr3 which are not included in first query, and than make union of those two queries... but I need some more direct approach (one sql statement if possible).

Thank you very much!

Answer 1

I think you probably need something like this:

Select attr1, attr2, attr3
from table
where attr1 is not null 
      or attr3 not in (select attr3 from table where attr1 is not null)