"Unique" and "distinct" are closely related words often used interchangeably, but they carry subtly different shades of meaning depending on context (everyday language, mathematics, or programming/databases).
In general/everyday English:
- Unique means being the only one of its kind — one-of-a-kind, unmatched, or unrepeatable. Something unique has no equal or duplicate anywhere. Example: "Every snowflake is unique."
- Distinct means clearly different or separate from something else, without necessarily implying there's only one. Example: "Red and blue are distinct colors" — they're different from each other, but that doesn't mean either color is one-of-a-kind in the world.
So "unique" emphasizes singularity (there is only one), while "distinct" emphasizes separateness or difference (this is not the same as that).
In databases and programming (SQL, spreadsheets, etc.):
- DISTINCT is used to remove duplicate rows/values from a result set, returning each different value only once. It doesn't restrict future data — it's simply about listing unique occurrences within a given query result.
- UNIQUE is often a constraint applied to a column or table, enforcing that no two rows can ever have the same value in that column. It's a rule about data integrity going forward, not just a way to view existing data.
For example, in SQL, SELECT DISTINCT city FROM customers returns a list of different city names appearing in the table, even if many customers share the same city. Meanwhile, a UNIQUE constraint on a "customer ID" column would prevent the database from ever storing two customers with the same ID.
In mathematics/set theory, "distinct elements" typically refers to elements that differ from one another within a set or list, while "unique" often describes an element that is the only one satisfying a particular condition (e.g., "there exists a unique solution").
In short: distinct = different from others; unique = the only one of its kind, or (in databases) enforced to never repeat.