Search on multiple tables with different columns

Question

I want to build a search engine for my website. My database table list is as follows:

1. d_name: I need to search on two columns.
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Answer 1

If you perform an UNION-query all seperate queries should have the same number of columns in the result. You can use fixed values like NULL, '' or 'not provided' to fill up the other tables.

Examlpe-query (demo)

SELECT column_1, column_2 FROM i_have_two_columns
UNION
SELECT column_1, NULL FROM i_have_only_one_column