layout: global title: Sampling Queries displayTitle: Sampling Queries license: | Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
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.
TABLESAMPLE ({ integer_expression | decimal_expression } PERCENT) | TABLESAMPLE ( integer_expression ROWS ) | TABLESAMPLE ( BUCKET integer_expression OUT OF integer_expression )
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| +--+----+