SQL TutorialLesson 4Free preview

SQL Select Distinct

This lesson is part of SQL · All levels

Summary

DISTINCT is used to eliminate duplicate values on the SELECT result. It's useful when you want to know a list of unique values, like the city where the customer came from. DISTINCT assesses the combinations of all selected columns, not each column separately.

Key points

The SELECT DISTINCT column returns only a unique value to that column.
In some columns, the combination of values that becomes the duplicate deletion reference.
DISTINCT is placed right after the SELECT keyword.
COUNT(DISTINCT column) calculates the number of unique values.
Value NULL is considered a distinct duplicate group by DISTINCT.

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