### 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>
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layout | title | displayTitle | license |
---|---|---|---|
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
(xROWS
): Sample the table down to the given number of rows.TABLESAMPLE
(xPERCENT
): Sample the table down to the given percentage. Note that percentages are defined as a number between 0 and 100.TABLESAMPLE
(BUCKET
xOUT OF
y): Sample the table down to ax
out ofy
fraction.
Note: TABLESAMPLE
returns the approximate number of rows or fraction requested.
Syntax
TABLESAMPLE ({ integer_expression | decimal_expression } PERCENT)
| TABLESAMPLE ( integer_expression ROWS )
| TABLESAMPLE ( BUCKET integer_expression OUT OF integer_expression )
Examples
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|
+--+----+