In my previous article, I introduced Azure Data Explorer, a powerful tool for storing and analyzing Big Data. In this article, we will dive deeper into the basics of Kusto Query Language (KQL) and explore its features and capabilities.
What is Kusto Query Language?
Kusto Query Language (KQL) is a read-only language used to process and retrieve data from Azure Data Explorer. It is designed to handle large datasets and offers excellent data ingestion and query performance. KQL shares similarities with SQL, making it easy for SQL users to learn and use.
Query Statement Types
KQL consists of two types of query statements: user query statements and application query statements.
User query statements are primarily used by users and include:
- Let statement: Used to break a long query into smaller named parts for easy understanding.
- Set statement: Sets a query option to define how the query is processed and the result is returned.
- Tabular expression statement: Returns data as a result in a tabular format.
Application query statements are designed to support scenarios where mid-tier applications take user queries and send a modified version of them to Kusto. These statements include:
- Alias statement: Defines an alias to another database in the same or different cluster.
- Pattern statement: Used by applications to inject themselves into the query name resolution process.
- Query parameters statement: Used by applications to protect against injection attacks.
- Restrict statement: Used by applications to restrict queries to a specific subset of data in Kusto.
Writing Kusto Queries
A Kusto query is a read-only request to process data and return the result. It consists of a sequence of query statements delimited by a semicolon. The result of the query is returned in a row-column format.
Here is an example of a Kusto query:
ls1
| where Winner == 1
| countIn this query, we are selecting records from the “ls1” table where the “Winner” column value is equal to 1, and then counting the number of records.
Common Operators in Kusto Queries
Kusto queries support various operators for data manipulation and analysis. Here are a few commonly used operators:
- Sort: Sorts the records of a table based on the specified column(s) in ascending or descending order.
- Take: Returns a specified number of records from a table.
- Project: Returns only the specified columns from a table.
- Where: Filters the records based on specified conditions.
- Summarize: Groups input rows based on specified columns and performs aggregate functions on each group.
- Render: Generates data visualizations from the query result data.
Control Commands
In addition to queries, KQL also supports control commands for processing and modifying data and metadata in Azure Data Explorer. Control commands are not part of the KQL syntax and start with the dot (.) operator.
Here are a few examples of control commands:
- Create table: Creates a new table with specified columns.
- Alter table: Modifies the structure of an existing table.
- Append: Adds records to a table from another table based on specified conditions.
- Show table: Displays the structure of a table.
- Drop table: Deletes a table.
Conclusion
Kusto Query Language (KQL) is a powerful tool for querying and analyzing large datasets in Azure Data Explorer. Its similarities with SQL make it easy for SQL users to learn and use. In this article, we explored the basics of KQL, including query statement types, common operators, and control commands.
Stay tuned for upcoming articles where we will dive deeper into KQL and explore more advanced features and techniques.