Set Operators
Set operators combine the results of two queries into a single result. Databend supports the following set operators:
INTERSECT
Returns all distinct rows selected by both queries.
Syntax
SELECT column1 , column2 ....
FROM table_names
WHERE condition
INTERSECT
SELECT column1 , column2 ....
FROM table_names
WHERE condition
Example
create table t1(a int, b int);
create table t2(c int, d int);
insert into t1 values(1, 2), (2, 3), (3 ,4), (2, 3);
insert into t2 values(2,2), (3, 5), (7 ,8), (2, 3), (3, 4);
select * from t1 intersect select * from t2;
Output:
2|3
3|4
EXCEPT
Returns All distinct rows selected by the first query but not the second.
Syntax
SELECT column1 , column2 ....
FROM table_names
WHERE condition
EXCEPT
SELECT column1 , column2 ....
FROM table_names
WHERE condition
Example
create table t1(a int, b int);
create table t2(c int, d int);
insert into t1 values(1, 2), (2, 3), (3 ,4), (2, 3);
insert into t2 values(2,2), (3, 5), (7 ,8), (2, 3), (3, 4);
select * from t1 except select * from t2;
Output:
1|2
UNION [ALL]
Combines rows from two or more result sets. Each result set must return the same number of columns, and the corresponding columns must have the same or compatible data types.
The command removes duplicate rows by default when combining result sets. To include duplicate rows, use UNION ALL.
Syntax
SELECT column1 , column2 ...
FROM table_names
WHERE condition
UNION [ALL]
SELECT column1 , column2 ...
FROM table_names
WHERE condition
[UNION [ALL]
SELECT column1 , column2 ...
FROM table_names
WHERE condition]...
[ORDER BY ...]
Example
CREATE TABLE support_team
(
NAME STRING,
salary UINT32
);
CREATE TABLE hr_team
(
NAME STRING,
salary UINT32
);
INSERT INTO support_team
VALUES ('Alice',
1000),
('Bob',
3000),
('Carol',
5000);
INSERT INTO hr_team
VALUES ('Davis',
1000),
('Eva',
4000);
-- The following code returns the employees in both teams who are paid less than 2,000 dollars:
SELECT NAME AS SelectedEmployee,
salary
FROM support_team
WHERE salary < 2000
UNION
SELECT NAME AS SelectedEmployee,
salary
FROM hr_team
WHERE salary < 2000
ORDER BY selectedemployee DESC;
Output:
Davis|1000
Alice|1000