WHERE clause
Description
The WHERE
clause is used to limit the results of the FROM
clause of a query or a subquery based on the specified condition.
Syntax
WHERE boolean_expression
Parameters
-
boolean_expression
Specifies any expression that evaluates to a result type
boolean
. Two or more expressions may be combined together using the logical operators (AND
,OR
).
Examples
CREATE TABLE person (id INT, name STRING, age INT);
INSERT INTO person VALUES
(100, 'John', 30),
(200, 'Mary', NULL),
(300, 'Mike', 80),
(400, 'Dan', 50);
-- Comparison operator in `WHERE` clause.
SELECT * FROM person WHERE id > 200 ORDER BY id;
+---+----+---+
| id|name|age|
+---+----+---+
|300|Mike| 80|
|400| Dan| 50|
+---+----+---+
-- Comparison and logical operators in `WHERE` clause.
SELECT * FROM person WHERE id = 200 OR id = 300 ORDER BY id;
+---+----+----+
| id|name| age|
+---+----+----+
|200|Mary|null|
|300|Mike| 80|
+---+----+----+
-- IS NULL expression in `WHERE` clause.
SELECT * FROM person WHERE id > 300 OR age IS NULL ORDER BY id;
+---+----+----+
| id|name| age|
+---+----+----+
|200|Mary|null|
|400| Dan| 50|
+---+----+----+
-- Function expression in `WHERE` clause.
SELECT * FROM person WHERE length(name) > 3 ORDER BY id;
+---+----+----+
| id|name| age|
+---+----+----+
|100|John| 30|
|200|Mary|null|
|300|Mike| 80|
+---+----+----+
-- `BETWEEN` expression in `WHERE` clause.
SELECT * FROM person WHERE id BETWEEN 200 AND 300 ORDER BY id;
+---+----+----+
| id|name| age|
+---+----+----+
|200|Mary|null|
|300|Mike| 80|
+---+----+----+
-- Scalar Subquery in `WHERE` clause.
SELECT * FROM person WHERE age > (SELECT avg(age) FROM person);
+---+----+---+
| id|name|age|
+---+----+---+
|300|Mike| 80|
+---+----+---+
-- Correlated Subquery in `WHERE` clause.
SELECT * FROM person AS parent
WHERE EXISTS (
SELECT 1 FROM person AS child
WHERE parent.id = child.id AND child.age IS NULL
);
+---+----+----+
|id |name|age |
+---+----+----+
|200|Mary|null|
+---+----+----+