2019-08-19 02:17:50 -04:00
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---
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layout: global
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title: Sampling Queries
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displayTitle: Sampling Queries
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license: |
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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---
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2020-04-09 20:39:34 -04:00
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### Description
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The `TABLESAMPLE` statement is used to sample the table. It supports the following sampling methods:
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* `TABLESAMPLE`(x `ROWS`): Sample the table down to the given number of rows.
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* `TABLESAMPLE`(x `PERCENT`): Sample the table down to the given percentage. Note that percentages are defined as a number between 0 and 100.
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* `TABLESAMPLE`(`BUCKET` x `OUT OF` y): Sample the table down to a `x` out of `y` fraction.
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Note: `TABLESAMPLE` returns the approximate number of rows or fraction requested.
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### Syntax
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{% highlight sql %}
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TABLESAMPLE ((integer_expression | decimal_expression) PERCENT)
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| TABLESAMPLE (integer_expression ROWS)
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| TABLESAMPLE (BUCKET integer_expression OUT OF integer_expression)
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{% endhighlight %}
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### Examples
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{% highlight sql %}
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SELECT * FROM test;
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+--+----+
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|id|name|
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+--+----+
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| 5|Alex|
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| 8|Lucy|
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| 2|Mary|
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| 4|Fred|
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| 1|Lisa|
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| 9|Eric|
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|10|Adam|
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| 6|Mark|
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| 7|Lily|
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| 3|Evan|
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+--+----+
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SELECT * FROM test TABLESAMPLE (50 PERCENT);
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+--+----+
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|id|name|
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+--+----+
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| 5|Alex|
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| 2|Mary|
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| 4|Fred|
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| 9|Eric|
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|10|Adam|
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| 3|Evan|
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+--+----+
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SELECT * FROM test TABLESAMPLE (5 ROWS);
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+--+----+
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|id|name|
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+--+----+
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| 5|Alex|
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| 8|Lucy|
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| 2|Mary|
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| 4|Fred|
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| 1|Lisa|
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+--+----+
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SELECT * FROM test TABLESAMPLE (BUCKET 4 OUT OF 10);
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+--+----+
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|id|name|
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+--+----+
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| 8|Lucy|
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| 2|Mary|
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| 9|Eric|
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| 6|Mark|
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+--+----+
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{% endhighlight %}
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### Related Statement
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* [SELECT](sql-ref-syntax-qry-select.html)
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