Understanding the KQL Parse Operator

A versatile operator, the parse operator allows you to evaluate a string expression and parse its value into one or more calculated columns.

The Kusto Query Language (KQL) is a powerful tool for querying large datasets in Azure Data Explorer, Azure Monitor, Microsoft Sentinel, and Microsoft Fabric. One of its versatile operators is the parse operator, which allows you to evaluate a string expression and parse its value into one or more calculated columns.

Syntax and Parameters

The basic syntax for the parse operator is:

T | parse [kind=kind [flags=regexFlags]] expression with [*] stringConstant columnName [:columnType] [*], ...

• T: The tabular input to parse.

• kind: Specifies the parsing mode (simple, regex, relaxed).

• regexFlags: Flags for regex mode (e.g., U for ungreedy, m for multi-line).

• expression: The string expression to evaluate.

• stringConstant: The string to search and parse.

• columnName: The name of the column to assign the parsed value.

• columnType: The type to convert the value to (default is string).

Supported Parsing Modes

1. Simple: Strict matching with regular string values.

2. Regex: Uses regular expressions for matching.

3. Relaxed: Allows partial matching, resulting in null values for unmatched types.

Practical Examples

Example 1: Parsing Developer Trace Statements

Consider a table with a column EventText containing strings like:

Event: NotifySliceRelease (resourceName=PipelineScheduler, totalSlices=27, sliceNumber=23, lockTime=02/17/2016 08:40:01, releaseTime=02/17/2016 08:40:01, previousLockTime=02/17/2016 08:39:01)

Using the parse operator, you can extend the table with individual columns for each value:

Traces | parse EventText with * "resourceName=" resourceName ", totalSlices=" totalSlices: long * "sliceNumber=" sliceNumber: long * "lockTime=" lockTime ", releaseTime=" releaseTime: date "," * "previousLockTime=" previousLockTime: date ")" *

Example 2: Extracting Email Alias and DNS

For a table with contact information, you can parse email addresses and website URLs:

Leads | parse Contacts with * "email=" alias: string "@" domain: string ", Website=https:" WebsiteDomain: string ")" | project EmailAddress=strcat(alias, "@", domain), EmailAlias=alias, WebsiteDomain

Advanced Usage with Regex Flags

In regex mode, you can use flags to control the parsing behavior. For example, to handle newlines and case insensitivity:

Traces | parse kind=regex flags=Ui EventText with * "resourceName=" resourceName ',' *

TLDR

The parse operator in KQL is a powerful tool for transforming and extracting data from string expressions. By understanding its syntax and modes, you can efficiently manipulate and analyze your data in Azure environments.