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4d516bece8
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[feature-wip](array-type)Add element_at and subscript functions (#8597)
Describe the overview of changes.
1. add function element_at;
2. support element_subscript([]) to get element of array, col_array[N] <==> element_at(col_array, N);
3. return error message instead of BE crash while array function execute failed;
element_at(array, index) desc:
> Returns element of array at given **(1-based)** index.
If **index < 0**, accesses elements from the last to the first.
Returns NULL if the index exceeds the length of the array or the array is NULL.
Usage example:
1. create table with ARRAY type column and insert some data:
```
+------+------+--------+
| k1 | k2 | k3 |
+------+------+--------+
| 1 | 2 | [1, 2] |
| 2 | 3 | NULL |
| 4 | NULL | [] |
| 3 | NULL | NULL |
+------+------+--------+
```
2. enable vectorized:
```
set enable_vectorized_engine=true;
```
3. element_subscript([]) usage example:
```
> select k1,k3,k3[1] from array_test;
+------+--------+----------------------------+
| k1 | k3 | %element_extract%(`k3`, 1) |
+------+--------+----------------------------+
| 3 | NULL | NULL |
| 1 | [1, 2] | 1 |
| 2 | NULL | NULL |
| 4 | [] | NULL |
+------+--------+----------------------------+
```
4. element_at function usage example:
```
> select k1,k3 from array_test where element_at(k3, -1) = 2;
+------+--------+
| k1 | k3 |
+------+--------+
| 1 | [1, 2] |
+------+--------+
```
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2022-04-02 12:03:56 +08:00 |
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