Query Data

This section covers how to perform queries against tables in the KDB.AI database.

Selecting the table to query

Each table in KDB.AI has an associated name. To perform a query, specify the name of the table in which the relevant data is stored. Using Python client you can create a table object from the session. The REST client is more direct with the table name supplied as a field in the JSON payload.

Python

documents = session.table("documents")

Queries

Obtain the data from the entire table using the following command:

PythonREST

documents.query()

curl -s -H "Content-Type: application/json" localhost:8082/data -d '{"table":"documents"}'

Filters

To select a subset of the data, you can apply filters as documented here. These serve as where clauses.

PythonREST

    results = table.query(filter=[("within","createdDate",["2020.07.10D15:00:00.0000", "2021.07.10D15:00:00.0000"]),("<=", "length", 100)])
    print(f'Results: {results}')

curl -s -H "Content-Type: application/json" localhost:8082/data \
-d '{"table":"documents","filter":[["within","createdDate",["2020.07.10D15:00:00.0000", "2021.07.10D15:00:00.0000"]],["<=", "length", 100]]}'

Processing results

You can return a subset of the columns in the table, reducing the amount of data sent back to the client.

PythonREST

documents.query(aggs=["author","content"])

curl -s -H "Content-Type: application/json" localhost:8082/data \
-d '{"table":"documents",agg=["author","content"]}'

In addition to returning a subset of the columns, you can return aggregated results, group by categorical variables, and sort based on a column name.

PythonREST

    table.query(aggs=[('sumLength','sum','length')], group_by=['author'], sort_by=['sumLength'])

curl -s -H "Content-Type: application/json" localhost:8082/data \
-d '{"table":"documents", 
agg=[["sumLength","sum","length"]],
groupBy=["author"],sortCols=["sumLength"]}'

Supported aggregations

The table below lists all supported aggregation functions.

Function	Description
`all`	Returns the logical 'and' of all values in a set.
`any`	Returns the logical 'or' of all values in a set.
`avg`	Calculates the mean value across the set of matching records.
`count`	Returns the number of records in the current selection.
`dev`	Calculates the standard deviation of a column.
`distinct`	Returns the distinct values from a column.
`first`	Returns the first occurrence of a value. This is useful when performing a group by aggregation.
`last`	Returns the last occurrence of a value. This is useful when performing a group by aggregation.
`max`	Takes the maximum value of a set of records.
`min`	Takes the minimum value of a set of records.
`prd`	Calculates the product of matching records.
`sdev`	Calculates the sample deviation of matching records.
`scov`	Calculates the sample covariance between matching records.
`sum`	Calculates the sum of matching records.
`svar`	Calculates the sample variance of matching records.
`var`	Calculates the variance of matching records.