A query is a read-only operation against a Kusto Engine cluster's ingested data. Queries always run in the context of a particular database in the cluster. They may also refer to data in another database, or even in another cluster.
As ad-hoc query of data is the top-priority scenario for Kusto, the Kusto Query Language syntax is optimized for non-expert users authoring and running queries over their data and being able to understand unambiguously what each query does (logically).
The language syntax is that of a data flow, where "data" means "tabular data" (data in one or more rows/columns rectangular shape). At a minimum, a query consists of source data references (references to Kusto tables) and one or more query operators applied in sequence, indicated visually by the use of a pipe character (
|) to delimit operators.
StormEvents | where State == 'FLORIDA' and StartTime > datetime(2000-01-01) | count
Each filter prefixed by the pipe character
| is an instance of an operator, with some parameters. The input to the operator is the table that is the result of the preceding pipeline. In most cases, any parameters are scalar expressions over the columns of the input.
In a few cases, the parameters are the names of input columns, and in a few cases, the parameter is a second table. The result of a query is always a table, even if it only has one column and one row.
T is used in query to denote the preceding pipeline or source table.