如何从一个表中合并两个不同查询的结果

Question

I am using MySQL in phpMyAdmin, I have a table from which I am trying to get the following result as illustrated below:

I have a table Rate structured as follows;

+---------+-----------+-------+--------+---------+----------+
| EntryID | RegDate   |  Code | Buying | Selling | Averages |
+---------+-----------+-------+--------+---------+----------+
| 1       |2013-11-08 |  USD  | NULL   | NULL    | 0.814    |
+---------+-----------+-------+--------+---------+----------+   
| 2       |2013-11-08 |  GBP  | NULL   | NULL    | 0.114    |
+---------+-----------+-------+--------+---------+----------+

With the primary key as EntryID I am trying to get the output as shown below;

+-----------+-------+-------+
| RegDate   |  USD  |  GBP  |
+-----------+-------+-------+
|2013-11-08 | 0.814 | 0.114 |
+---------+---------+-------+ 

Answer 1

SELECT RegDate,
       SUM(CASE WHEN Code='USD' THEN Averages ELSE 0 END) as USD,
       SUM(CASE WHEN Code='GBP' THEN Averages ELSE 0 END) as GBP
FROM T
GROUP BY RegDate

SQLFiddle demo

Answer 2

SELECT USD.RegDate, USD.Averages as USD,
GBP.Averages as GBP From
(SELECT RegDate, Averages
From Table1 where Code = 'USD') USD
Inner join
(SELECT RegDate, Averages
From Table1 where Code = 'GBP') GBP
ON USD.RegDate = GBP.RegDate

Sample Fiddle

Answer 3

You can simply JOIN the table with itself, use the table once for each currency you need;

SELECT usd.RegDate, usd.averages USD, gbp.averages GBP
FROM Table1 usd
JOIN Table1 gbp
  ON usd.regdate = gbp.regdate
 AND usd.code = 'USD'
 AND gbp.code = 'GBP';

An SQLfiddle to test with .

Note that this query assumes that each currency exists exactly once per date to give a good result, if that's not the case, you should add that to your sample data.

Answer 4

Try:

SELECT EntryID, regDate,
SUM(CASE Code WHEN 'USD' THEN Averages ELSE 0 END) as USD,
SUM(CASE Code WHEN 'GBP' THEN Averages ELSE 0 END) as GBP
FROM TableA
GROUP BY regDate

See Demo