Databases · Junior · Question 2 of 75

What is a primary key?

✓Correct answer: A column (or set of columns) that uniquely identifies each row and cannot be NULL
2A password needed to open the table
3The first column of any table

Explanation

A table has at most one primary key. The database automatically creates a unique index for it, so lookups by primary key are fast.

Further reading

PostgreSQL: Constraints ↗

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