Well, I'm not sure about the "most efficient" way, since efficiency in general depends on which database system...
you're using, whether there are indexes, and so on.
Your query would be something like this:
select case when ( select count(distinct datecol) from yourtable ) > 1 then ( select max(datecol) from yourtable ) else null end
Notice that if there are not more than 1 distinct values in datecol, the query returns NULL. You didn't say what you wanted in that situation.
Dig Deeper on Oracle and SQL
Related Q&A from Rudy Limeback
Read an example of an SQL case expression from our SQL expert Rudy Limeback. Continue Reading
Read SQL expert Rudy Limeback's advice for counting combinations in a table with SQL's GROUP BY clause Continue Reading
Read about the Mimer Validator, a tool used to verify your SQL code, in this tip from SQL expert Rudy Limeback. Continue Reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.