1b780f364b
### What changes were proposed in this pull request? Add Coalesce/Repartition/Repartition_By_Range Hints to SQL Reference ### Why are the changes needed? To make SQL reference complete ### Does this PR introduce _any_ user-facing change? <img width="1100" alt="Screen Shot 2020-05-29 at 6 46 38 PM" src="https://user-images.githubusercontent.com/13592258/83316782-d6fcf300-a1dc-11ea-87f6-e357b9c739fd.png"> <img width="1099" alt="Screen Shot 2020-05-29 at 6 43 30 PM" src="https://user-images.githubusercontent.com/13592258/83316784-d8c6b680-a1dc-11ea-95ea-10a1f75dcef9.png"> Only the the above pages are changed. The following two pages are the same as before. <img width="1100" alt="Screen Shot 2020-05-28 at 10 05 27 PM" src="https://user-images.githubusercontent.com/13592258/83223474-bfb3fc00-a12f-11ea-807a-824a618afa0b.png"> <img width="1099" alt="Screen Shot 2020-05-28 at 10 05 08 PM" src="https://user-images.githubusercontent.com/13592258/83223478-c2165600-a12f-11ea-806e-a1e57dc35ef4.png"> ### How was this patch tested? Manually build and check Closes #28672 from huaxingao/coalesce_hint. Authored-by: Huaxin Gao <huaxing@us.ibm.com> Signed-off-by: Sean Owen <srowen@gmail.com>
94 lines
2.2 KiB
Markdown
94 lines
2.2 KiB
Markdown
---
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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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### 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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```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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```
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### Examples
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```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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```
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### Related Statements
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* [SELECT](sql-ref-syntax-qry-select.html) |