mysql - Select from table if record found in another table

Question

I need to select some rows from Table 1 lets say if a value is found in Table 2. So I want to check if the value (I will enter the value from command line) is found in Table 2 and then select rows from Table1, if not I want to select rows from another table. I tried CASE but from what I got that works only if you want to check for value within one table. Any idea?

Answer 1

You can do something like this:

-- If value is found in table2, select from table1
select * -- <- use padding if necessary 
  from table1
 where exists (select 1
                 from table2
                where myField = value)

union all

-- If value is not found in table2, select from another_Table
select * -- <- use padding if necessary
  from another_Table
 where not exists (select 1
                     from table2
                    where myField = value)