Hi list I realized the following behaviour of UNION ALL: SELECT 'a' AS col1, 'b' AS col2 UNION ALL SELECT 'c' AS col1, 'd' AS col2; returns: col1 | col2 ------+------ a | b c | d Now I switch the column aliases in the second SELECT-Statement: SELECT 'a' AS col1, 'b' AS col2 UNION ALL SELECT 'c' AS col2, 'd' AS col1; This returns the same result: col1 | col2 ------+------ a | b c | d Same behaviour when working just with column names, no aliases. So my conclusion is that the result of UNION ALL depends on the column order, not on the column names or aliases. Is this the intended behaviour? And is it documented somewhere? What I found is the last sentence on https://www.postgresql.org/docs/current/queries-union.html which says "[...] they return the same number of columns and the corresponding columns have compatible data types [...]" It says nothing about column order, column names or aliases. Does this obviously imply it's the column order? Thank you for some clarification. Andy
