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).

Examples

Given the Data Set DS_1:

Input DS_1 (see structure)

Id_1	Id_2	Id_3	Me_1	Me_2	At_1
2010	A	XX	20	36	E
2010	A	YY	4	9	F
2010	B	XX	9	10	F

Example 1

DS_r := DS_1 [ keep Me_1 ];

results in (see structure):

DS_r

Id_1	Id_2	Id_3	Me_1
2010	A	XX	20
2010	A	YY	4
2010	B	XX	9