合并具有相同数据结构的两个表，然后联接到另一个表

Question

The two tables with the same data structure:

    issues:                        old_issues:
    |id|itemno|issuedate |         |id|itemno|issuedate |
    |1 |200   |2018-02-01|         |1 |200   |2017-12-21|
    |2 |300   |2018-02-03|         |2 |200   |2017-12-20|
    |3 |200   |2018-02-02|         |3 |400   |2016-05-09|
                                   |4 |500   |2016-07-10|

I want to merge these two tables into a new_issues table, then I want to join it to another table that looks like this:

items:
|itemnumber|location|ccode|
|200       |DEP     |ARACD|
|300       |DEP     |ARACD|
|400       |SYD     |ARACD|
|500       |DEP     |DVD  |

But I only want to select the items with a query like this:

SELECT * FROM items WHERE location = 'DEP' AND ccode = 'ARACD'

And select the new_issues that meet this criteria:

SELECT * FROM new_issues WHERE issuedate < '2018-01-01'

This is what I have tried, but it seems to hang there loading forever as there are millions of rows in the issues tables:

SELECT i.itemno, new_issues.issuedate
FROM (SELECT * FROM issues UNION SELECT * FROM old_issues) AS new_issues
RIGHT JOIN items i ON i.itemno = new_issues.itemno
WHERE i.ccode = 'ARACD' AND i.location = 'DEP' AND new_issues.issuedate < '2018-01-01'

Answer 1

Not sure if this is what you're looking for but have you tried a UNION SELECT ?

SELECT * FROM newitems WHERE location = 'DEP' AND ccode = 'ARACD'
UNION SELECT * FROM olditems WHERE location = 'DEP' AND ccode = 'ARACD' GROUP BY itemno