| layout | title | displayTitle | license |
|---|---|---|---|
global |
SELECT |
WHERE clause |
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|
The WHERE clause is used to limit the results of the FROM
clause of a query or a subquery based on the specified condition.
{% highlight sql %} WHERE boolean_expression {% endhighlight %}
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).
{% highlight sql %} 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|
+---+----+----+
{% endhighlight %}