How to compare two tables in postgres

I want compare two column values which come from two different queries.开发者_如何转开发 Can anyone suggest a query which compares two columns in Postgres?

Well, the easiest to understand--but not necessarily the fastest--is probably something like this. (But you might mean something else by "compare".)

-- Values in column1 that aren't in column2.
SELECT column1 FROM query1 
WHERE column1 NOT IN (SELECT column2 FROM query2);

-- Values in column2 that aren't in column1.
SELECT column2 FROM query2 
WHERE column2 NOT IN (SELECT column1 FROM query1);

-- Values common to both column1 and column2
SELECT q1.column1 FROM query1 q1
INNER JOIN query2 q2 ON (q1.column1 = q2.column2);

You can also do this in a single statement to give you a visual comparison. A FULL OUTER JOIN returns all the values in both columns, with matching values in the same row, and NULL where one column is missing a value that's in the other column.

SELECT q1.column1, q2.column2 FROM query1 q1
FULL OUTER JOIN query2 q2 ON (q1.column1 = q2.column2);