# Logical Data Modeling - Duplicate

A duplicate happens when in a set two elements have an equivalence relationship that returns true.

## Example

• In the set {1,1,2,3}, 1 is a duplicate
• The set {1,2,3} has no duplicate

### Data Processing Operation

relational operators can create duplicates but no all.

See below:

Operator Symbol Creates Duplicates?
Selection σ No
Projection π Yes
Cross-product × No
Set-difference No
Union Yes
Join No

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