---
{
    "title": "size",
    "language": "zh-CN"
}
---

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## size (cardinality)

### description

#### Syntax

```
BIGINT size(ARRAY<T> arr) 
BIGINT cardinality(ARRAY<T> arr)
```

返回数组中元素数量，如果输入数组为NULL，则返回NULL

### notice

`仅支持向量化引擎中使用`

### example

```
mysql> set enable_vectorized_engine=true;

mysql> select k1,k2,size(k2) from array_test;
+------+-----------+------------+
| k1   | k2        | size(`k2`) |
+------+-----------+------------+
|    1 | [1, 2, 3] |          3 |
|    2 | []        |          0 |
|    3 | NULL      |       NULL |
+------+-----------+------------+

mysql> select k1,k2,cardinality(k2) from array_test;
+------+-----------+-------------------+
| k1   | k2        | cardinality(`k2`) |
+------+-----------+-------------------+
|    1 | [1, 2, 3] |                 3 |
|    2 | []        |                 0 |
|    3 | NULL      |              NULL |
+------+-----------+-------------------+
```

### keywords

SIZE, CARDINALITY