Maintaining Components: keep

Syntax

op [ keep comp {, comp }* ]

Input parameters

op	the operand
comp	a Component to keep

Examples of valid syntaxes

::: DS_1 [ keep Me_2, Me_3 ]

Semantics for scalar operations

This operator cannot be applied to scalar values.

Input parameters type

op

dataset

comp

name<component>

Result type

result

dataset

Additional Constraints

All the Components comp must belong to the input Data Set op.

The Components comp cannot be Identifiers in op.

Behaviour

The operator takes as input a Data Set (op) and some Component names of such a Data Set (comp). These Components can be Measures or Attributes of op but not Identifiers. The operator maintains the specified Components, drops all the other dependent Components of the Data Set (Measures and Attributes) and maintains the independent Components (Identifiers) unchanged. This operation corresponds to a projection in the usual relational join semantics (specifying which columns will be projected in among Measures and Attributes).