# groupby algorithm does not cover "select distinct" case

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#### Details

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: V4.0_CS02
• Fix Version/s:
• Component/s:
• Labels:
None
• Environment:

Applied

• Proposal:
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Add a sentence to step 2 of the four-step algorithm:

Applies set transformations to each subset according to the second parameter, resulting in a new set of potentially different structure and cardinality. If the second parameter is absent, transforms each subset into a set consisting of a single instance without properties,

Rephrase the later remark about "select distinct":

If the second parameter can be is omitted, steps 2 and 3 produce one instance containing only the grouping properties per to request distinct value combination of the grouping properties.

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Add a sentence to step 2 of the four-step algorithm: Applies set transformations to each subset according to the second parameter, resulting in a new set of potentially different structure and cardinality. If the second parameter is absent, transforms each subset into a set consisting of a single instance without properties, Rephrase the later remark about "select distinct": If the second parameter can be is omitted, steps 2 and 3 produce one instance containing only the grouping properties per to request distinct value combination of the grouping properties.
• Resolution:
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#### Description

The four-step algorithm given at the beginning of the groupby transformation does not describe what happens for Products?\$apply=groupby((Category)). According to a later remark, this is supposed to select only the distinct Categories. But, after step 1, I have two subsets

ID Category Name Color TaxRate
P1 PG1 Sugar White 0.06
P2 PG1 Coffee Brown 0.06

and

ID Category Name Color TaxRate
P3 PG2 Paper White 0.14
P4 PG2 Pencil Black 0.14

Step 2 cannot be carried out due to lack of a second parameter. Step 3 has no effect. Step 4 concatenates these two subsets again, so that the overall effect is of groupby((Category),identity).

To keep the case without second parameter within the four-step framework, step 2 must essentially produce an instance without properties, leading to subsets

ID Category Name Color TaxRate

and

ID Category Name Color TaxRate

which step 3 would then change to

ID Category Name Color TaxRate
PG1

and

ID Category Name Color TaxRate
PG2

#### People

• Assignee:
Unassigned
Reporter:
Heiko Theissen
• Watchers:
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#### Dates

• Created:
Updated:
Resolved: