spark-instrumented-optimizer/docs/sql-ref-syntax-qry-select-where.md

---
layout: global
title: SELECT
displayTitle: WHERE clause
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  this work for additional information regarding copyright ownership.
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---
The <code>WHERE</code> clause is used to limit the results of the <code>FROM</code>
clause of a query or a subquery based on the specified condition.

### Syntax
{% highlight sql %}
WHERE boolean_expression
{% endhighlight %}

### Parameters
<dl>
  <dt><code><em>boolean_expression</em></code></dt>
  <dd>
    Specifies any expression that evaluates to a result type <code>boolean</code>. Two or
    more expressions may be combined together using the logical 
    operators ( <code>AND</code>, <code>OR</code> ).
  </dd>
</dl>

### Examples
{% 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 column reference in `WHERE` clause of subquery.
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 %}

### Related Clauses
- [SELECT Main](sql-ref-syntax-qry-select.html)
- [GROUP BY Clause](sql-ref-syntax-qry-select-groupby.html)
- [HAVING Clause](sql-ref-syntax-qry-select-having.html)
- [ORDER BY Clause](sql-ref-syntax-qry-select-orderby.html)
- [SORT BY Clause](sql-ref-syntax-qry-select-sortby.html)
- [CLUSTER BY Clause](sql-ref-syntax-qry-select-clusterby.html)
- [DISTRIBUTE BY Clause](sql-ref-syntax-qry-select-distribute-by.html)
- [LIMIT Clause](sql-ref-syntax-qry-select-limit.html)