Sql – Difference between Select Unique and Select Distinct

sqlsql-server

I thought these were synonomous, but I wrote the following in Microsoft SQL:

Select Unique col from 
     (select col from table1 union select col from table2) alias

And it failed. Changing it to

Select Distinct col from 
     (select col from table1 union select col from table2) alias

fixed it. Can someone explain?

Best Solution

SELECT UNIQUE is old syntax supported by Oracle's flavor of SQL. It is synonymous with SELECT DISTINCT.

Use SELECT DISTINCT because this is standard SQL, and SELECT UNIQUE is non-standard, and in database brands other than Oracle, SELECT UNIQUE may not be recognized at all.