In my MySQL database I have two tables: investments
(with a currency_id
and the date
of investment) and currencies
(with data like name, etc).
I would like to select the minimum date
for each currency inside investments table and then join this result with currencies
.
The query I imagined would work may make this clearer:
SELECT T.currency_id, T.mindate
FROM (
SELECT * , MIN( DATE ) AS mindate
FROM investments
GROUP BY investments.currency_id
ORDER BY mindate ASC
) AS T
JOIN currencies ON T.currency_id =
currencies.currency_id
However, all I get is the subquery result, and nothing from currencies table is joined. What am I doing wrong?
In SELECT
clause, you forget to get currencies
columns' values. Add currencies.*
at the first line.
SELECT T.currency_id, T.mindate, currencies.*
FROM (
SELECT * , MIN( DATE ) AS mindate
FROM investments
GROUP BY investments.currency_id
ORDER BY mindate ASC
) AS T
JOIN currencies ON T.currency_id =
currencies.currency_id
However you forgot to select the column[s] from currencies but still it would may not give you the desired output because in the subquery you are selecting all the columns and grouping by only currency_id
. the query may not run or group by all the rest of columns where group function is not added so you may get unexpected results. So, I would like to suggest the following way instead
SELECT T.currency_id, T.mindate, u.currency_name
FROM (
SELECT currency_id, MIN(DATE) AS mindate
FROM investments
GROUP BY investments.currency_id) AS T
JOIN currencies u ON u.currency_id = t.currency_id
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