如何使用查询在表中选择最新日期

Question

This is what I did, which is wrong. My date field is stored as (MM/DD/YYYY)

Select Name,Family,ID,max(Dates) from MyTable group by name,family

Answer 1

If Dates is a TEXT column containing values stored as MM/DD/YYYY , calling MAX() on it doesn't produce the latest date because Sqlite will do an alphanumeric sort on the column, which will sort by month first.

You need to properly convert the Dates TEXT values into DATE values and then when you call MAX() on the DATE values, Sqlite will sort the way you expect and produce the latest date value.

DATE values can be created using DATE() but the parameter to DATE() needs to be a date string in ISO format ( YYYY-MM-DD ). So, we need to parse out the existing TEXT string values using substr(), then build an ISO date from the parsed-out date part components, then finally pass that ISO date into DATE() as the parameter.

But, a side effect of this is that the query output will now show the max date in ISO format, so if you need the date in the original format, you would need to include that separately.

So, something like this:

SELECT Name, Family, ID, Dates, MAX(DATE(SUBSTR(Dates, 7, 4) || '-' || SUBSTR(Dates, 1, 2) || '-' || SUBSTR(Dates, 4, 2))) FROM MyTable