Data type conversion functions - Log Service - Alibaba Cloud Documentation Center

You can use type conversion functions to convert data to the correct type in a query statement.


Function	Syntax	Description
cast function	cast(`x` as `type`)	Converts the values of the `x` field as a data type. If the cast function cannot convert a value, the query that calls this function fails.
try_cast function	try_cast(`x` as `type`)	Converts the values of the `x` as a data type. If the try_cast function cannot convert a value, the function returns NULL. The query that calls this function can process the NULL value and continue to run. Note A log may contain data of the data types that you do not expect. When you query logs, we recommend that you use the try_cast function. This way, conversion failures will not cause your queries fail.
typeof function	typeof(`x`)	Returns the data type of the `x` field.

cast function

The cast function is used to convert the values of the x field to a specified data type. If the cast function cannot convert a value, the query that calls this function fails.

Syntax

cast(x as type)

Parameters


Parameter	Description
`x`	The value of this parameter can be of any data type.
`type`	A SQL data type. Valid values: bigint, varchar, double, boolean, timestamp, decimal, array, and map. Example: `cast(json_parse( key) as array(varchar))`. Each SQL data type maps to a data type that you can use in a Log Service index. For information about the mapping, see Data type mappings.

Return value type

The data type that is specified by the type parameter.

Examples

Converts number 1 to the boolean data type.

Query statement
```
* | select cast(1 as boolean)
```
Query result

try_cast function

Converts the values of the x field to a specified data type. If the try_cast function cannot convert a value, the function returns NULL. The query that calls this function can process the NULL value and continue to run.

Syntax

try_cast(x as type)

Parameters


Parameter	Description
`x`	The value of this parameter can be of any data type.
`type`	A SQL data type. Valid values: bigint, varchar, double, boolean, timestamp, decimal, array, and map. Example: `try_cast(json_parse( key) as map(varchar, varchar))`. Each SQL data type maps to a data type that you can use in a Log Service index. For information about the mapping, see Data type mappings.

Return value type

The data type that the type parameter specifies.

Examples

Converts the values of the uid field to the varchar data type.

Query statement
```
* | select try_cast(uid as varchar)
```
Query result

typeof function

Returns the data type of the x field.

Syntax

typeof(x)

Parameters


Parameter	Description
`x`	The value of this parameter can be of any data type.

Return value type

Data of the varchar data type.

Examples

Returns the data type of the request_time field.

Query statement
```
* |SELECT typeof(request_time)
```
Query result

Data type mappings

The following table describes the mappings between the SQL data types and the data types that are supported by a Log Service index.


Data types that are supported by Log Service index	SQL data type
long	bigint
text	varchar
double	double
json	varchar