sql: improve aggregation docs #657
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Incorrectly stated only-full-group-by was not supported.
zz-jason
reviewed
Oct 9, 2018
sql/aggregate-group-by-functions.md
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| | [`STDDEV_SAMP()`](https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_stddev-samp) | Return the sample standard deviation | | ||
| | [`VARIANCE()`](https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_variance) | Return the population standard variance | | ||
| | [`VAR_POP()`](https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_var-pop) | Return the population standard variance | | ||
| | [`JSON_ARRAYAGG()`](https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_json-arrayagg) | Return result set as a single JSON array | |
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these functions are not supported yet, their PRs are in review.
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I left a comment in the description- I will move them to ‘unsupported’ if they do not merge before review of this PR is complete
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I've updated the PR to only include merged functions. PTAL @zz-jason
lilin90
reviewed
Oct 11, 2018
sql/aggregate-group-by-functions.md
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| ## GROUP BY modifiers | ||
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| TiDB dose not support any `GROUP BY` modifiers currently. We'll do it in the future. For more information, see [#4250](https://github.com/pingcap/tidb/issues/4250). | ||
| TiDB does not currently support `GROUP BY` modifiers such as `WITH ROLLUP`. We plan to add support in the future. See [TIDB #4250](https://github.com/pingcap/tidb/issues/4250). |
sql/aggregate-group-by-functions.md
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| TiDB performs equivalent to MySQL with sql mode [`ONLY_FULL_GROUP_BY`](https://dev.mysql.com/doc/refman/5.7/en/sql-mode.html#sqlmode_only_full_group_by) being disabled: permits the `SELECT` list, `HAVING` condition, or `ORDER BY` list to refer to non-aggregated columns even if the columns are not functionally dependent on `GROUP BY` columns. | ||
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| For example, this query is illegal in MySQL 5.7.5 with `ONLY_FULL_GROUP_BY` enabled because the non-aggregated column "b" in the `SELECT` list does not appear in the `GROUP BY`: | ||
| TiDB supports the SQL Mode `ONLY_FULL_GROUP_BY`, and when enabled TiDB will refuse queries with ambiguous non-aggregated columns. For example, this query is illegal with `ONLY_FULL_GROUP_BY` enabled because the non-aggregated column "b" in the `SELECT` list does not appear in the `GROUP BY`: |
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the GROUP BY -> the GROUP BY statement
OR:
the GROUP BY -> the GROUP BY
sql/aggregate-group-by-functions.md
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| ``` | ||
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| The preceding query is legal in TiDB. TiDB does not support SQL mode `ONLY_FULL_GROUP_BY` currently. We'll do it in the future. For more inmormation, see [#4248](https://github.com/pingcap/tidb/issues/4248). | ||
| TiDB does not currently enable [`ONLY_FULL_GROUP_BY`](mysql-compatibility.md#default-differences) mode by default. |
sql/aggregate-group-by-functions.md
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| ### Differences from MySQL | ||
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| The current implementation of `ONLY_FULL_GROUP_BY` is less strict than in MySQL 5.7. For example, suppose that we execute the following query, expecting the results to be ordered by "c": |
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than in MySQL -> than that in MySQL
sql/aggregate-group-by-functions.md
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| ## Detection of functional dependence | ||
| ## Unsupported aggregate functions | ||
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| The following aggregate functions are currently unsupported in TiDB. You can track our progress in [TIDB #7623](https://github.com/pingcap/tidb/issues/7623): |
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- Remove one extra space before "You can". Only leave one.
- TIDB 7623 -> TiDB 7623
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I've removed the yet-to-be-merged functions, so it is easier to review. |
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zz-jason
approved these changes
Oct 19, 2018
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Incorrectly stated only-full-group-by was not supported.
Note: This PR references aggregate functions that are in development and have not been merged yet. If they are not complete after review, I will move them to the unsupported functions section.