Can I check if a table exists before join?

Question

I have the following problem. I have Table A and would like to join to table B if table B exists. Can this be done? I am only writing SQL in WorkBench to try achieve it.

I am aware I cannot use the EXISTS option as I have tried typing it out but it prompts for an error.

Any suggestions would be greatly appreciated.

Thanks.

Answer 1

I managed to do this using EXECUTE, so using a query that is only prepared at runtime:

SET @sqlCommand = IF(
    EXISTS (SELECT column_name FROM information_schema.columns WHERE table_schema = '{{yourschemaname}}' AND table_name = '{{yourtablename}}' AND column_name = '{{yourcolumnname}}'), 
    'SELECT \'Yes! Good to go!\' as ColumnExists',
    'SELECT \'Nope!\' as ColumnExists');
PREPARE executable FROM @sqlCommand;
EXECUTE executable;

Note that the two selects at the center (Yes!/No!) are the custom statements that are to be executed conditionally. So if the column exists, the first command is executed (select 'yes!'), otherwise the second one (select 'nope').

I got the hint from this discussion here.. have a look if you're looking for the MSSQL equivalent: https://ask.sqlservercentral.com/questions/97579/check-if-table-exists-in-join.html