Getting started with Kusto

Azure Data Explorer is a service for storing and running interactive analytics on big data.

It is based on relational database management systems, supporting entities such as databases, tables, and columns. Complex analytical queries are performed using the Kusto Query Language. Some query operators include calculated columns, searching and filtering or rows, group by-aggregates, and joins.

The service offers excellent data ingestion and query performance by "sacrificing" the ability to perform in-place updates of individual rows and cross-table constraints/transactions. Therefore, it supplements, rather than replaces, traditional RDBMS systems for scenarios such as OLTP and data warehousing.

Structured, semi-structured (e.g. JSON-like nested types), and unstructured (free text) data are handled equally well.

Interacting with Azure Data Explorer

The main way for users to interact with Kusto is by using one of the many available client tools. While SQL queries are supported, the primary means of interaction is through the use of the Kusto query language to send data queries, and through the use of control commands to manage entities, discover metadata, etc. Both queries and control commands are basically short textual "programs".

Kusto queries

A query is a read-only request to process data and return the results of this processing, without modifying the data or metadata. Kusto queries can use the SQL language, or the Kusto query language. As an example for the latter, the following query counts how many rows in the Logs table have the value of the Level column equals the string Critical:

| where Level == "Critical"
| count

Queries cannot start with the dot (.) character or the hash (#) character.

Control commands

Control commands are requests to Kusto to process and potentially modify data or metadata. For example, the following control command creates a new Kusto table with two columns, Level and Text:

.create table Logs (Level:string, Text:string)

Control commands have their own syntax (which isn't part of the Kusto Query Language syntax, although the two share many concepts). In particular, control commands are distinguished from queries by having the first character in the text of the command be the dot (.) character (which can't start a query). This distinction prevents many kinds of security attacks, simply because this prevents embedding control commands inside queries.

Not all control commands modify data or metadata. A large class of commands, the commands that start with .show, are used to display metadata or data. For example, the .show tables command returns a list of all tables in the current database.