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spark-instrumented-optimizer/docs/sql-ref-syntax-qry-sampling.md
Huaxin Gao 75da05038b [MINOR][SQL][DOCS] Remove two leading spaces from sql tables 
### What changes were proposed in this pull request?
Remove two leading spaces from sql tables.

### Why are the changes needed?

Follow the format of other references such as https://docs.snowflake.com/en/sql-reference/constructs/join.html, https://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_10002.htm, https://www.postgresql.org/docs/10/sql-select.html.

### Does this PR introduce any user-facing change?

before
```
SELECT * FROM  test;
  +-+
  ...
  +-+
```
after
```
SELECT * FROM  test;
+-+
...
+-+
```

### How was this patch tested?
Manually build and check

Closes #28348 from huaxingao/sql-format.

Authored-by: Huaxin Gao <huaxing@us.ibm.com>
Signed-off-by: gatorsmile <gatorsmile@gmail.com>
2020-05-01 10:11:43 -07:00

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global Sampling Queries Sampling Queries 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 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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