Retrieve results from a table based on conditions

I have a query with SQL as it needs an expertise. I have two tables Table A and B. Now I need to retrieve results from table 1 based on some conditions and i also need to retrieve results from table 1 based on results from table 2.

I want to achieve

Select * from table1 where author ="xyz") + select * from table1 where id=""
—>id = select post_ID from table2 where author = “abc”

So the ID values of table1 matches the post_ID values of table 2

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