Return just the last day of each month with SQL

Question

I have a table that contains multiple records for each day of the month, over a number of years. Can someone help me out in writing a query that will only return the last d

Answer 1

SQL Server (other DBMS will work the same or very similarly):

SELECT
  *
FROM
  YourTable
WHERE
  DateField IN (
    SELECT   MAX(DateField)
    FROM     YourTable
    GROUP BY MONTH(DateField), YEAR(DateField)
  )

An index on DateField is helpful here.

PS: If your DateField contains time values, the above will give you the very last record of every month, not the last day's worth of records. In this case use a method to reduce a datetime to its date value before doing the comparison, for example this one.