PIVOT Clause
Description
The PIVOT clause is used for data perspective. We can get the aggregated values based on specific column values, which will be turned to multiple columns used in SELECT clause. The PIVOT clause can be specified after the table name or subquery.
Syntax
PIVOT ( { aggregate_expression [ AS aggregate_expression_alias ] } [ , ... ]
FOR column_list IN ( expression_list ) )
Parameters
-
aggregate_expression
Specifies an aggregate expression (SUM(a), COUNT(DISTINCT b), etc.).
-
aggregate_expression_alias
Specifies an alias for the aggregate expression.
-
column_list
Contains columns in the
FROMclause, which specifies the columns we want to replace with new columns. We can use brackets to surround the columns, such as(c1, c2). -
expression_list
Specifies new columns, which are used to match values in
column_listas the aggregating condition. We can also add aliases for them.
Examples
CREATE TABLE person (id INT, name STRING, age INT, class INT, address STRING);
INSERT INTO person VALUES
(100, 'John', 30, 1, 'Street 1'),
(200, 'Mary', NULL, 1, 'Street 2'),
(300, 'Mike', 80, 3, 'Street 3'),
(400, 'Dan', 50, 4, 'Street 4');
SELECT * FROM person
PIVOT (
SUM(age) AS a, AVG(class) AS c
FOR name IN ('John' AS john, 'Mike' AS mike)
);
+------+-----------+---------+---------+---------+---------+
| id | address | john_a | john_c | mike_a | mike_c |
+------+-----------+---------+---------+---------+---------+
| 200 | Street 2 | NULL | NULL | NULL | NULL |
| 100 | Street 1 | 30 | 1.0 | NULL | NULL |
| 300 | Street 3 | NULL | NULL | 80 | 3.0 |
| 400 | Street 4 | NULL | NULL | NULL | NULL |
+------+-----------+---------+---------+---------+---------+
SELECT * FROM person
PIVOT (
SUM(age) AS a, AVG(class) AS c
FOR (name, age) IN (('John', 30) AS c1, ('Mike', 40) AS c2)
);
+------+-----------+-------+-------+-------+-------+
| id | address | c1_a | c1_c | c2_a | c2_c |
+------+-----------+-------+-------+-------+-------+
| 200 | Street 2 | NULL | NULL | NULL | NULL |
| 100 | Street 1 | 30 | 1.0 | NULL | NULL |
| 300 | Street 3 | NULL | NULL | NULL | NULL |
| 400 | Street 4 | NULL | NULL | NULL | NULL |
+------+-----------+-------+-------+-------+-------+