SELECT Lists

Duplicate Rows Are Preserved

Plain SELECT preserves duplicate output rows.

highlighted = computed this step

Duplicate rows are preserved

Plain SELECT does not remove duplicate output rows.

plain SELECT keeps duplicates\text{plain SELECT keeps duplicates}

Read duplicate facts

The output has 2 repeated rows, and distinctApplied is no.

duplicate rows=2\text{duplicate rows}=2

SELECT-list examples are tiny finite-table transforms; DISTINCT, aggregation, type coercion, optimizer behavior, and database-product claims are out of scope.

Duplicate rows are preserved: base rowsitemqtybonusstatuspen31openmug20opencup21closedtagNULL1open SELECT list itemspositionkindsourceoutput0columnstatusstatus SELECT output rowsstatusopenopenclosedopen SELECT factsfactvalueinputRowCount4outputRowCount4outputColumnCount1duplicateOutputRows2rowOrdersource_orderdistinctAppliedno

No DISTINCT step

This book models plain SELECT lists only, so no deduplication step runs.

DISTINCT not applied\text{DISTINCT not applied}

Summary

SELECT chooses cells; DISTINCT is a separate operation.

duplicates visible\text{duplicates visible}