Query parameters declaration statement

  • Article

Queries sent to Kusto may include a set of name or value pairs. The pairs are called query parameters, together with the query text itself. The query may reference one or more values, by specifying names and type, in a query parameters declaration statement.

Query parameters have two main uses:

  • As a protection mechanism against injection attacks.
  • As a way to parameterize queries.

In particular, client applications that combine user-provided input in queries that they then send to Kusto should use the mechanism to protect against the Kusto equivalent of SQL Injection attacks.

Declaring query parameters

To reference query parameters, the query text, or functions it uses, must first declare which query parameter it uses. For each parameter, the declaration provides the name and scalar type. Optionally, the parameter can also have a default value. The default is used if the request doesn't provide a concrete value for the parameter. Kusto then parses the query parameter's value, according to its normal parsing rules for that type.

Syntax

declare query_parameters ( Name1 : Type1 [= DefaultValue1] [,...] );

Learn more about syntax conventions.

Parameters

Name Type Required Description
Name1 string ✔️ The name of a query parameter used in the query.
Type1 string ✔️ The corresponding type, such as string or datetime. The values provided by the user are encoded as strings. The appropriate parse method is applied to the query parameter to get a strongly-typed value.
DefaultValue1 string A default value for the parameter. This value must be a literal of the appropriate scalar type.

Note

  • Like user defined functions, query parameters of type dynamic cannot have default values.
  • Let, set, and tabular statements are strung together/separated by a semicolon, otherwise they will not be considered part of the same query.

Example

Run the query

declare query_parameters(maxInjured:long = 90);
StormEvents 
| where InjuriesDirect + InjuriesIndirect > maxInjured
| project EpisodeId, EventType, totalInjuries = InjuriesDirect + InjuriesIndirect

Output

EpisodeId EventType totalInjuries
12459 Winter Weather 137
10477 Excessive Heat 200
10391 Heat 187
10217 Excessive Heat 422
10217 Excessive Heat 519

Specify query parameters in a client application

The names and values of query parameters are provided as string values by the application making the query. No name may repeat.

The interpretation of the values is done according to the query parameters declaration statement. Every value is parsed as if it were a literal in the body of a query. The parsing is done according to the type specified by the query parameters declaration statement.

REST API

Query parameters are provided by client applications through the properties slot of the request body's JSON object, in a nested property bag called Parameters. For example, here's the body of a REST API call to Kusto that calculates the age of some user, presumably by having the application ask for the user's birthday.

{
    "ns": null,
    "db": "myDB",
    "csl": "declare query_parameters(birthday:datetime); print strcat(\"Your age is: \", tostring(now() - birthday))",
    "properties": "{\"Options\":{},\"Parameters\":{\"birthday\":\"datetime(1970-05-11)\",\"courses\":\"dynamic(['Java', 'C++'])\"}}"
}

Kusto SDKs

To learn how to provide the names and values of query parameters when using Kusto client libraries, see Use query parameters to protect user input.

Kusto.Explorer

To set the query parameters sent when making a request to the service, use the Query parameters "wrench" icon (ALT + P).

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