beliefer opened a new pull request #27429: [SPARK-28330][SQL] Support ANSI SQL: result offset clause in query expression URL: https://github.com/apache/spark/pull/27429 ### What changes were proposed in this pull request? This is a ANSI SQL and feature id is `F861` ``` <query expression> ::= [ <with clause> ] <query expression body> [ <order by clause> ] [ <result offset clause> ] [ <fetch first clause> ] <result offset clause> ::= OFFSET <offset row count> { ROW | ROWS } ``` For example: ``` SELECT customer_name, customer_gender FROM customer_dimension WHERE occupation='Dancer' AND customer_city = 'San Francisco' ORDER BY customer_name; customer_name | customer_gender ----------------------+----------------- Amy X. Lang | Female Anna H. Li | Female Brian O. Weaver | Male Craig O. Pavlov | Male Doug Z. Goldberg | Male Harold S. Jones | Male Jack E. Perkins | Male Joseph W. Overstreet | Male Kevin . Campbell | Male Raja Y. Wilson | Male Samantha O. Brown | Female Steve H. Gauthier | Male William . Nielson | Male William Z. Roy | Male (14 rows) SELECT customer_name, customer_gender FROM customer_dimension WHERE occupation='Dancer' AND customer_city = 'San Francisco' ORDER BY customer_name OFFSET 8; customer_name | customer_gender -------------------+----------------- Kevin . Campbell | Male Raja Y. Wilson | Male Samantha O. Brown | Female Steve H. Gauthier | Male William . Nielson | Male William Z. Roy | Male (6 rows) ``` There are some mainstream database support the syntax. **PostgreSQL:** https://www.postgresql.org/docs/11/queries-limit.html **Vertica:** https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/SQLReferenceManual/Statements/SELECT/OFFSETClause.htm?zoom_highlight=offset **MySQL:** https://dev.mysql.com/doc/refman/5.6/en/select.html The description for design: **1**. Consider `OFFSET` as the special case of `LIMIT`. For example: `SELECT * FROM a limit 10;` similar to `SELECT * FROM a limit 10 offset 0;` `SELECT * FROM a offset 10;` similar to `SELECT * FROM a limit -1 offset 10;` **2**. Because the current implement of `LIMIT` has good performance. For example: `SELECT * FROM a limit 10;` parsed to the logic plan as below: ``` GlobalLimit (limit = 10) |--LocalLimit (limit = 10) ``` and then the physical plan as below: ``` GlobalLimitExec (limit = 10) // Take the first 10 rows globally |--LocalLimitExec (limit = 10) // Take the first 10 rows locally ``` This operator reduce massive shuffle and has good performance. Sometimes, the logic plan transformed to the physical plan as: ``` CollectLimitExec (limit = 10) // Take the first 10 rows globally ``` If the SQL contains order by, such as `SELECT * FROM a order by c limit 10;`. This SQL will be transformed to the physical plan as below: ``` TakeOrderedAndProjectExec (limit = 10) // Take the first 10 rows after sort globally ``` Based on this situation, this PR produces the following operations. For example: `SELECT * FROM a limit 10 offset 10;` parsed to the logic plan as below: ``` GlobalLimit (limit = 10, offset = 10) |--LocalLimit (limit = 10, offset = 10) ``` and then the physical plan as below: ``` GlobalLimitExec (limit = 10, offset = 10) // Skip the first 10 rows and take the next 10 rows globally |--LocalLimitExec (limit = 10, offset = 10) // Take the first 20(limit + offset) rows locally ``` Sometimes, the logic plan transformed to the physical plan as: ``` CollectLimitExec (limit = 10, offset = 10) // Skip the first 10 rows and take the next 10 rows globally ``` If the SQL contains order by, such as `SELECT * FROM a order by c limit 10 offset 10;`. This SQL will be transformed to the physical plan as below: ``` TakeOrderedAndProjectExec (limit = 10, offset 10) // Skip the first 10 rows and take the next 10 rows after sort globally ``` **3**.In addition to the above, there is a special case that is only offset but no limit. For example: `SELECT * FROM a offset 10;` parsed to the logic plan as below: ``` GlobalLimit (limit = -1, offset = 10) // -1 means invalid |--LocalLimit (limit = -1, offset = 10) // -1 means invalid ``` If offset is very large, will generate a lot of overhead. So I add a configuration item `spark.sql.forceUsingOffsetWithoutLimit` to force running query when user knows the offset is small enough. The default value of `spark.sql.forceUsingOffsetWithoutLimit` is false. Note: The origin PR to support this feature is https://github.com/apache/spark/pull/25416. Because the origin PR too old, there exists massive conflict which is hard to resolve. So I open this new PR to support this feature. ### Why are the changes needed? new feature ### Does this PR introduce any user-facing change? 'No' ### How was this patch tested? Exists and new UT
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