SQL从前一天选择最大值

Question

I have a table with DateTime and Value columns. I need to select max value from the last day (newest) day. The best I could come up with is 3 step process:

1. SELECT MAX(DateTime) FROM MyTable
2. get rid of time part in datetime, store date
3. SELECT MAX(Value) FROM MyTable WHERE DateTime>date

Is there a better way to do this?

Answer 1

Your three steps in one query would be

SELECT MAX(Value)
FROM MyTable
WHERE DateTime >= CAST( (SELECT MAX(DateTime)FROM MyTable) AS DATE)

Now finding the max date could be quite expensive query so if you're actually after the yesterday's max value then you should use CURRENT_DATE instead, ie

WHERE DateTime >= ( CURRENT_DATE - 1 ) AND DateTime < CURRENT_DATE

Answer 2

If you mean the highest value of today , then you can use:

SELECT MAX(value)
FROM MyTable
WHERE CAST(DateTime AS DATE) = CURRENT_DATE

Answer 3

Can you just do this?

SELECT MAX(Value)
FROM MyTable
WHERE DateTime IN (
    SELECT MAX(DateTime)
    FROM MyTable
)