如何比较Postgres中的两个表 [英] How to compare two tables in postgres

问题描述

我想比较来自两个不同查询的两个列值。有人可以建议比较Postgres中两列的查询吗？

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

推荐答案

最容易理解，但不一定最快-大概是这样的。 （但是您可能会通过比较来表示其他含义。）

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);

您也可以在单个语句中进行此操作以进行直观比较。 FULL OUTER JOIN 返回两列中的所有值，并且在同一行中具有匹配的值，而 NULL 其中一个

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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