Question

I want to be able to select values from either column, where column a or b is not the value I specify.

Let me explain more.

I have a table, of buddies on a website, like this:

  columna     |    columnb
  6774                887
  887                 2423
  3434                 887
  3434                 6774
  887                 3455
  887                 33444
  343434              2343

Columna tells you who sent the request.

Our user is currently 887, how using MySQL can I find out who he is friends with?

Thanks

Answer 1

SELECT (CASE WHEN columna = 887 THEN columnb ELSE columna END) AS 'columnAlias'
FROM <table>
WHERE columna = 887
      OR columnb = 887

Edit: For using the result of the above query to get details records from another table…

Using JOIN:

SELECT T2.*
FROM Table2 AS T2
     INNER JOIN (SELECT (CASE WHEN columna = 887 THEN columnb ELSE columna END) AS 'columnAlias'
                 FROM Table1
                 WHERE columna = 887
                       OR columnb = 887) AS _Temp ON _Temp.columnAlias = T2.ForeignKeyColumn

Using Nested Query:

SELECT T2.*
FROM Table2 AS T2
WHERE T2.ForeignKeyColumn IN (SELECT (CASE WHEN columna = 887 THEN columnb ELSE columna END) AS 'columnAlias'
                              FROM Table1
                              WHERE columna = 887
                                    OR columnb = 887)