如何选择在给定日期尚未更新的MySQL表值？

Question

I have a MySQL database named mydb in which I store daily share prices for 423 companies in a table named data. Table data has the following columns:

`epic`, `date`, `open`, `high`, `low`, `close`, `volume`

epic and date being primary key pairs. I update the data table each day using a csv file which would normally have 423 rows of data all having the same date. However, on some days prices may not available for all 423 companies and data for a particular epic and date pair will not be updated. In order to determine the missing pair I have resorted to comparing a full list of epics against the incomplete list of epics using two simple SELECT queries with different dates and then using a file comparator, thus revealing the missing epic(s). This is not a very satisfactory solution and so far I have not been able to construct a query that would identify any epics that have not been updated for any particular day.

SELECT `epic`, `date` FROM `data`
WHERE `date` IN ('2019-05-07', '2019-05-08')
ORDER BY `epic`, `date`;

Produces pairs of values:

`epic`  `date`
"3IN"   "2019-05-07"
"3IN"   "2019-05-08"
"888"   "2019-05-07"
"888"   "2019-05-08"
"AA."   "2019-05-07"
"AAL"   "2019-05-07"
"AAL"   "2019-05-08"

Where in this case AA. has not been updated on 2019-05-08. The problem with this is that it is not easy to spot a value that is not a pair. Any help with this problem would be greatly appreciated.

Answer 1

You could do a COUNT on epic, with a GROUP BY epic for items in that date range and see if you get any with a COUNT less than 2, then select from this result where UpdateCount is less than 2, forgive me if the syntax on the column names is not correct, I work in SQL Server, but the logic for the query should still work for you.

SELECT x.epic
FROM
(
    SELECT COUNT(*) AS UpdateCount, epic
    FROM data
    WHERE date IN ('2019-05-07', '2019-05-08')
    GROUP BY epic
) AS x
WHERE x.UpdateCount < 2

Answer 2

Assuming you only want to check the last date uploaded, the following will return every item not updated on 2019-05-08:

SELECT last_updated.epic, last_updated.date
FROM (
SELECT epic , max(`date`) AS date FROM `data`
GROUP BY 'epic'
) AS last_updated
WHERE 'date' <> '2019-05-08'
ORDER BY 'epic'
;

or for any upload date, the following will compare against the entire database, so you don't rely on '2019-08-07' having every epic row. Ie if the epic has been in the database before then it will show if not updated:

SELECT d.epic, max(d.date)
FROM data as d
WHERE d.epic NOT IN (
   SELECT d2.epic 
   FROM data as d2 
   WHERE d2.date = '2019-05-08'
)
GROUP BY d.epic
ORDER BY d.epic