join two tables into one big table

Question

I have two tables with the same columns, and I need to copy one table's rows to the other table's rows to create one big table with all the values from both tables. Right now I am doing this query to return the same thing:

SELECT col1, col2, col3 from Table1
union
SELECT col1, col2, col3 from Table2

However, it seems horribly inefficient, and on my system is very slow (returns 1210189 records).

Answer 1

May it work to just do:

SELECT col1, col2, col3 
INTO Table1
FROM Table2 

Answer 2

Start with union all:

select col1, col2, col3 from Table1
union all
select col1, col2, col3 from Table2

Your query is trying to deduplicate things, which would slow it down considerably.