How to make a selection from 4 tables into 1 PostgreSQL table?

Question

PostgreSQL

There are 4 SQL tables.
Let's call them BTC_BUY, BTC_SELL, ETH_BUY, ETH_SELL.
Each table has 2 fields UNIXDATE, AMOUNT.
We need to make one table
UNIXDATE, ACTION, CURRENCY, AMOUNT
where ACTION is just a BUY or SELL record, depending on which table we selected the data from.
where CURRENCY is a BTC or ETH entry depending on which table is from.
Sort by UNIXDATE in ascending order.

Answer 1

So it is possible:

INSERT INTO RESULTS (UNIXDATE, ACTION, CURRENCY, AMOUNT)
SELECT bb.UNIXDATE, 'BUY', 'BTC', bb.AMOUNT FROM BTC_BUY bb
UNION ALL
SELECT bs.UNIXDATE, 'SELL', 'BTC', bs.AMOUNT FROM BTC_SELL bs
UNION ALL
SELECT eb.UNIXDATE, 'BUY', 'ETH', eb.AMOUNT FROM ETH_BUY eb
UNION ALL
SELECT es.UNIXDATE, 'SELL', 'ETH', es.AMOUNT FROM ETH_SELL es
ORDER BY UNIXDATE ASC;