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

---
layout: global
title: Sampling Queries
displayTitle: Sampling Queries
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  this work for additional information regarding copyright ownership.
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---

### Description

The `TABLESAMPLE` statement is used to sample the table. It supports the following sampling methods:
  * `TABLESAMPLE`(x `ROWS`): Sample the table down to the given number of rows.
  * `TABLESAMPLE`(x `PERCENT`): Sample the table down to the given percentage. Note that percentages are defined as a number between 0 and 100.
  * `TABLESAMPLE`(`BUCKET` x `OUT OF` y): Sample the table down to a `x` out of `y` fraction.

Note: `TABLESAMPLE` returns the approximate number of rows or fraction requested.

### Syntax

{% highlight sql %}
TABLESAMPLE ((integer_expression | decimal_expression) PERCENT)
    | TABLESAMPLE (integer_expression ROWS)
    | TABLESAMPLE (BUCKET integer_expression OUT OF integer_expression)
{% endhighlight %}

### Examples

{% highlight sql %}
SELECT * FROM test;
  +--+----+
  |id|name|
  +--+----+
  | 5|Alex|
  | 8|Lucy|
  | 2|Mary|
  | 4|Fred|
  | 1|Lisa|
  | 9|Eric|
  |10|Adam|
  | 6|Mark|
  | 7|Lily|
  | 3|Evan|
  +--+----+

SELECT * FROM test TABLESAMPLE (50 PERCENT);
  +--+----+
  |id|name|
  +--+----+
  | 5|Alex|
  | 2|Mary|
  | 4|Fred|
  | 9|Eric|
  |10|Adam|
  | 3|Evan|
  +--+----+

SELECT * FROM test TABLESAMPLE (5 ROWS);
  +--+----+
  |id|name|
  +--+----+
  | 5|Alex|
  | 8|Lucy|
  | 2|Mary|
  | 4|Fred|
  | 1|Lisa|
  +--+----+

SELECT * FROM test TABLESAMPLE (BUCKET 4 OUT OF 10);
  +--+----+
  |id|name|
  +--+----+
  | 8|Lucy|
  | 2|Mary|
  | 9|Eric|
  | 6|Mark|
  +--+----+
{% endhighlight %}

### Related Statement

  * [SELECT](sql-ref-syntax-qry-select.html)