Union :

-> By using unions we can combine rows present in the two or more tables into the result set. -> Union operation will eliminate duplicate rows or records. -> In case of joins columns data from two or more tables is included into the result set. -> In case of unions rows data from two or more tables is included into the result set. Ex: create table t1 ( c1 int, c2 varchar(40),c3 int ) create table t2 ( c4 int,c5 varchar(40),c6 int ) select * from t1, select * from t2 select * from t1 union select * from t2--->this query will execute and gives coorect output select c1,c3,c2 from t1 union select c4,c5,c6 from t2--->this query will fail select c1,c2,c3 from t1 union select c4,c5,c6 from t2--->this query will execute and gives correct output

Union all:

Is same as union operation but only exception is union all operation will fetch or display duplicate records into the result set. Ex:select * from t1 union all select * from t2.