What is the difference between UNION and UNION ALL?

91.

They both are the same thing , the server will treat them differently

Union All is the abbreviation of Union they both do the same.

UNION only selects distinct values, UNION ALL selects all values

UNION will filter the table before the resultset , while Union All does the same but at the end

Union All does not exist

ALL - Incorporates all rows into the results. This includes duplicates. If not specified, duplicate rows are removed