Union Select Query

Hello,

I recently took over a database that was not properly designed by the person who crteated it. I have created a UNION SELECT query from four tables in my database and am haveing trouble with records being duplicated. Can anyone tell what I need to do to get rid of the duplicate records? My code looks similar to this:

SELECT [column1], [column2], [column3], [colunm4]
FROM table1
WHERE [column1] is not null

UNION SELECT [column1], [column2], [column3], [colunm4]
FROM table2
WHERE [column1] is not null

UNION SELECT [column1], [column2], [column3], [colunm4]
FROM table3
WHERE [column1] is not null

UNION SELECT [column1], [column2], [column3], [colunm4]
FROM table4
WHERE [column1] is not null

ORDER BY [column1];

I would appreciate any advice, inspiration, and guidence?

Kindest regards,
EA