mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-10-20 23:41:01 +00:00
06aa03f1a7
* Doc fixes: rm anchors <a> * Doc fixes: rm anchors <a> * Doc fixes: fix links * Doc fixes: fix the links
83 lines
2.4 KiB
Markdown
83 lines
2.4 KiB
Markdown
# Array(T) {#data_type-array}
|
||
|
||
由 `T` 类型元素组成的数组。
|
||
|
||
`T` 可以是任意类型，包含数组类型。 但不推荐使用多维数组，ClickHouse 对多维数组的支持有限。例如，不能存储在 `MergeTree` 表中存储多维数组。
|
||
|
||
## 创建数组
|
||
|
||
您可以使用array函数来创建数组：
|
||
|
||
```
|
||
array(T)
|
||
```
|
||
|
||
您也可以使用方括号：
|
||
|
||
```
|
||
[]
|
||
```
|
||
|
||
创建数组示例：
|
||
|
||
```
|
||
:) SELECT array(1, 2) AS x, toTypeName(x)
|
||
|
||
SELECT
|
||
[1, 2] AS x,
|
||
toTypeName(x)
|
||
|
||
┌─x─────┬─toTypeName(array(1, 2))─┐
|
||
│ [1,2] │ Array(UInt8) │
|
||
└───────┴─────────────────────────┘
|
||
|
||
1 rows in set. Elapsed: 0.002 sec.
|
||
|
||
:) SELECT [1, 2] AS x, toTypeName(x)
|
||
|
||
SELECT
|
||
[1, 2] AS x,
|
||
toTypeName(x)
|
||
|
||
┌─x─────┬─toTypeName([1, 2])─┐
|
||
│ [1,2] │ Array(UInt8) │
|
||
└───────┴────────────────────┘
|
||
|
||
1 rows in set. Elapsed: 0.002 sec.
|
||
```
|
||
|
||
## 使用数据类型
|
||
|
||
ClickHouse会自动检测数组元素,并根据元素计算出存储这些元素最小的数据类型。如果在元素中存在[NULL](../query_language/syntax.md#null-literal)或存在[Nullable](nullable.md#data_type-nullable)类型元素，那么数组的元素类型将会变成[Nullable](nullable.md)。
|
||
|
||
如果 ClickHouse 无法确定数据类型，它将产生异常。当尝试同时创建一个包含字符串和数字的数组时会发生这种情况 (`SELECT array(1, 'a')`)。
|
||
|
||
自动数据类型检测示例：
|
||
|
||
```
|
||
:) SELECT array(1, 2, NULL) AS x, toTypeName(x)
|
||
|
||
SELECT
|
||
[1, 2, NULL] AS x,
|
||
toTypeName(x)
|
||
|
||
┌─x──────────┬─toTypeName(array(1, 2, NULL))─┐
|
||
│ [1,2,NULL] │ Array(Nullable(UInt8)) │
|
||
└────────────┴───────────────────────────────┘
|
||
|
||
1 rows in set. Elapsed: 0.002 sec.
|
||
```
|
||
|
||
如果您尝试创建不兼容的数据类型数组，ClickHouse 将引发异常：
|
||
|
||
```
|
||
:) SELECT array(1, 'a')
|
||
|
||
SELECT [1, 'a']
|
||
|
||
Received exception from server (version 1.1.54388):
|
||
Code: 386. DB::Exception: Received from localhost:9000, 127.0.0.1. DB::Exception: There is no supertype for types UInt8, String because some of them are String/FixedString and some of them are not.
|
||
|
||
0 rows in set. Elapsed: 0.246 sec.
|
||
```
|