unique()

A key: at most one row per combination of cols.

Usage

Source

unique(*cols)

In requires it is an assumption about an input (checked on the data when the input is bound to a backend); in ensures it is proved by Rel.keys_sound from the input keys and the transformation.

Parameters

*cols: str

The names of the key’s columns.

Returns

Unique

A Unique condition, for requires or ensures.