Join Tables MySQL | 易学教程

问题

I have multiple tables and made 2 sub-selects (UserRecord,CustomerRecord) that i would like to merge into 1 table

UserRecord
========================
| RecordID | UserName |
========================
| 1        | Sara     |
| 1        | Tom      |
| 2        | Sara     |
| 2        | Kurt     |
| 3        | Fre      |
========================

Table: CustomerRecord
============================
| RecordID | CustomerName |
============================
| 1        | Jef          |
| 2        | Alex         |
| 2        | Peter        |
============================

Table: This should be the result
=======================================
| RecordID | UserName | CustomerName | 
=======================================
| 1        | Sara     | -            |
| 1        | Tom      | -            |
| 1        | -        | Jef          |
| 2        | Sara     | -            |
| 2        | Kurt     | -            |
| 2        | -        | Alex         |
| 2        | -        | Peter        |
| 3        | Fre      | -            |
=======================================

- = null

I tried with left, right, left outer, right outer ... join on the 2 tables but i don't get what i would like.

SELECT *
FROM UserRecord AS ur
INNER JOIN CustomerRecord AS cr ON ur.RecordID = cr.RecordID;

回答1:

What you want is not a join, but a UNION:

SELECT RecordID, UserName, NULL AS CustomerName FROM UserRecord
UNION
SELECT RecordID, NULL AS UserName, CustomerName FROM CustomerRecord

... which just appends records from the two tables.

I'd just add that the order will not be the one you have shown in your expected result. If order is important then you should SELECT from this UNION and add an explicit ORDER BY clause on this outer select. Something like:

SELECT * FROM (
    SELECT RecordID, UserName, NULL AS CustomerName FROM UserRecord
    UNION
    SELECT RecordID, NULL AS UserName, CustomerName FROM CustomerRecord
) ORDER BY RecordID, UserName, CustomerName

回答2:

You can use a simple union

select recordid, username, null as customername from userrecord
union
select recordid, null, customername from customerrecord

来源：https://stackoverflow.com/questions/23264116/join-tables-mysql

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