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Document pivot and unpivot operators (#15669)

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Katya Macedo 2024-01-25 11:53:39 -06:00 committed by GitHub
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7
docs/querying/sql-operators.md
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@ -108,3 +108,10 @@ Also see the [CONCAT function](sql-scalar.md#string-functions).
|`x NOT IN (values)`|True if _x_ is not one of the listed values|
|`x IN (subquery)`|True if _x_ is returned by the subquery. This will be translated into a join; see [Query translation](sql-translation.md) for details.|
|`x NOT IN (subquery)`|True if _x_ is not returned by the subquery. This will be translated into a join; see [Query translation](sql-translation.md) for details.|
## Other operators
|Operator|Description|
|--------|-----------|
|`PIVOT (aggregation_function(column_to_aggregate) FOR column_with_values_to_pivot IN (pivoted_column1 [, pivoted_column2 ...]))`|Carries out an aggregation and transforms rows into columns in the output.|
|`UNPIVOT (values_column FOR names_column IN (unpivoted_column1 [, unpivoted_column2 ... ]))`|Transforms existing column values into rows.|

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docs/querying/sql.md
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@ -57,6 +57,8 @@ Druid SQL supports SELECT queries with the following structure:
[ WITH tableName [ ( column1, column2, ... ) ] AS ( query ) ]
SELECT [ ALL | DISTINCT ] { * | exprs }
FROM { <table> | (<subquery>) | <o1> [ INNER | LEFT ] JOIN <o2> ON condition }
[PIVOT (aggregation_function(column_to_aggregate) FOR column_with_values_to_pivot IN (pivoted_column1 [, pivoted_column2 ...]))]
[UNPIVOT (values_column FOR names_column IN (unpivoted_column1 [, unpivoted_column2 ... ]))]
[ CROSS JOIN UNNEST(source_expression) as table_alias_name(column_alias_name) ]
[ WHERE expr ]
[ GROUP BY [ exprs | GROUPING SETS ( (exprs), ... ) | ROLLUP (exprs) | CUBE (exprs) ] ]
@ -85,6 +87,121 @@ FROM clause, metadata tables are not considered datasources. They exist only in
For more information about table, lookup, query, and join datasources, refer to the [Datasources](datasource.md)
documentation.
## PIVOT
:::info
The PIVOT operator is an [experimental feature](../development/experimental-features.md).
:::
The PIVOT operator carries out an aggregation and transforms rows into columns in the output.
The following is the general syntax for the PIVOT operator. Note that the PIVOT operator is enclosed in parentheses and forms part of the FROM clause of the query.
```sql
PIVOT (aggregation_function(column_to_aggregate)
FOR column_with_values_to_pivot
IN (pivoted_column1 [, pivoted_column2 ...])
)
```
PIVOT syntax parameters:
* `aggregation_function`: An aggregation function, such as SUM, COUNT, MIN, MAX, or AVG.
* `column_to_aggregate`: The source column to be aggregated.
* `column_with_values_to_pivot`: The column that contains values for the pivoted column names.
* `pivoted_columnN`: The list of values to pivot into headers in the output.
The following example demonstrates how to transform `cityName` values into column headers `ba_sum_deleted` and `ny_sum_deleted`:
```sql
SELECT user, channel, ba_sum_deleted, ny_sum_deleted
FROM "wikipedia"
PIVOT (SUM(deleted) AS "sum_deleted" FOR "cityName" IN ( 'Buenos Aires' AS ba, 'New York' AS ny))
WHERE ba_sum_deleted IS NOT NULL OR ny_sum_deleted IS NOT NULL
LIMIT 15
```
<details>
<summary> View results </summary>
|`user`|`channel`|`ba_sum_deleted`|`ny_sum_deleted`|
|------|---------|----------------|----------------|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|69.86.6.150|`#en.wikipedia`|null|1|
|190.123.145.147|`#es.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|16|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|190.192.179.192|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
|181.230.118.178|`#en.wikipedia`|0|null|
</details>
## UNPIVOT
:::info
The UNPIVOT operator is an [experimental feature](../development/experimental-features.md).
:::
The UNPIVOT operator transforms existing column values into rows.
Note that UNPIVOT isn't the exact reverse operation of PIVOT. The PIVOT operator carries out an aggregation and merges rows as needed. UNPIVOT doesn't reproduce the original rows that have been merged.
The following is the general syntax for the UNPIVOT operator. Note that the UNPIVOT operator is enclosed in parentheses and forms part of the FROM clause of the query.
```sql
UNPIVOT (values_column
FOR names_column
IN (unpivoted_column1 [, unpivoted_column2 ... ])
)
```
UNPIVOT syntax parameters:
* `values_column`: The column that contains the values of the unpivoted columns.
* `names_column`: The column that contains the names of the unpivoted columns.
* `unpivoted_columnN`: The list of columns to transform into rows in the output.
The following example demonstrates how to transform the columns `added` and `deleted` into row values that correspond to a particular `channel`:
```sql
SELECT channel, user, action, SUM(changes) AS total_changes
FROM "wikipedia"
UNPIVOT ( changes FOR action IN ("added", "deleted") )
WHERE channel LIKE '#ar%'
GROUP BY channel, user, action
LIMIT 15
```
<details>
<summary> View results </summary>
|`channel`|`user`|`action`|`total_changes`|
|---------|------|--------|---------------|
|`#ar.wikipedia`|156.202.189.223|added|0|
|`#ar.wikipedia`|156.202.189.223|deleted|30|
|`#ar.wikipedia`|156.202.76.160|added|0|
|`#ar.wikipedia`|156.202.76.160|deleted|0|
|`#ar.wikipedia`|156.212.124.165|added|451|
|`#ar.wikipedia`|156.212.124.165|deleted|0|
|`#ar.wikipedia`|160.166.147.167|added|1|
|`#ar.wikipedia`|160.166.147.167|deleted|0|
|`#ar.wikipedia`|185.99.32.50|added|1|
|`#ar.wikipedia`|185.99.32.50|deleted|0|
|`#ar.wikipedia`|197.18.109.148|added|0|
|`#ar.wikipedia`|197.18.109.148|deleted|24|
|`#ar.wikipedia`|`2001:16A2:3C7:6C00:917E:AD28:FAD3:FD5C`|added|1|
|`#ar.wikipedia`|`2001:16A2:3C7:6C00:917E:AD28:FAD3:FD5C`|deleted|0|
|`#ar.wikipedia`|41.108.33.83|added|0|
</details>
## UNNEST
The UNNEST clause unnests ARRAY typed values. The source for UNNEST can be an array type column, or an input that's been transformed into an array, such as with helper functions like [`MV_TO_ARRAY`](./sql-multivalue-string-functions.md) or [`ARRAY`](./sql-array-functions.md).
@ -139,7 +256,6 @@ WHERE stringDim IN ('1', '2', '3')
Note that explicit type casting does not lead to significant performance improvement when comparing strings and numbers involving numeric dimensions since numeric dimensions are not indexed.
## GROUP BY
The GROUP BY clause refers to columns in the FROM table. Using GROUP BY, DISTINCT, or any aggregation functions will
@ -283,9 +399,4 @@ To solve this issue, explicitly provide the type of the dynamic parameter using
```
SELECT * FROM druid.foo WHERE dim1 like CONCAT('%', CAST (? AS VARCHAR), '%')
```
```

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@ -778,6 +778,10 @@ APPROX_COUNT_DISTINCT_DS_THETA
APPROX_QUANTILE_DS
DS_QUANTILES_SKETCH
APPROX_QUANTILE_FIXED_BUCKETS
# Operators
pivoted
UNPIVOT
unpivoted
# File specific overrides
100x
_common