How to compare two tables in postgres

问题:

I want compare two column values which come from two different queries. Can anyone suggest a query which compares two columns in Postgres?

回答1:

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); 

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