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Add a note about reading subcolumns from Array type in documentation

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Kruglov Pavel 2024-07-16 13:08:25 +02:00 committed by GitHub
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docs/en/sql-reference/data-types/array.md
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@ -96,3 +96,22 @@ Result:
│ 1 │ [2] │ [[4,1]] │
└───────────┴───────────┴───────────┘
```
## Reading nested subcolumns from Array
If nested type `T` inside `Array` has subcolumns (for example, if it's a [named tuple](./tuple.md)), you can read its subcolumns from an `Array(T)` type with the same subcolumn names. The type of a subcolumn will be `Array` of the type of original subcolumn.
**Example**
```sql
CREATE TABLE t_arr (arr Array(Tuple(field1 UInt32, field2 String))) ENGINE = MergeTree ORDER BY tuple();
INSERT INTO t_arr VALUES ([(1, 'Hello'), (2, 'World')]), ([(3, 'This'), (4, 'is'), (5, 'subcolumn')]);
SELECT arr.field1, toTypeName(arr.field1), arr.field2, toTypeName(arr.field2) from t_arr;
```
```test
┌─arr.field1─┬─toTypeName(arr.field1)─┬─arr.field2────────────────┬─toTypeName(arr.field2)─┐
│ [1,2] │ Array(UInt32) │ ['Hello','World'] │ Array(String) │
│ [3,4,5] │ Array(UInt32) │ ['This','is','subcolumn'] │ Array(String) │
└────────────┴────────────────────────┴───────────────────────────┴────────────────────────┘
```