Union, intersection and difference operations in SQL

SQL It's not the same in China 、 hand over 、 Difference operation

1、 hand over （ Corresponding to the intersection operation in the set ,A∩B)
notes ： Returns the same part of the query result, that is, their intersection , Want to keep all duplicates , Must use INTERSECT ALL Instead of INTERSECT

（select * from table1） intersect （select * from table2）

2、 Difference set （ Corresponding to the difference set operation in the set ,A-B）
notes ： Return the row records that are different from the second query result in the first query result ,
That is, the difference set of two results ,EXCEPT The operation automatically removes duplicates , If you want to keep all the repetitions , Must use EXCEPT ALL Instead of EXCEPT..oracle of use minus Realization

（select * from table1） except（select * from table2）

3、 Combine （ Corresponding to the union operation in the set ,AUB）
notes ：UNION The operation automatically removes duplicates , Want to keep all duplicates , You have to use UNION ALL Instead of UNION

（select * from table1） union（select * from table2）