Unique Key

Unique Key
1. A unique key can allow null values. (You can define a unique key on columns that allow nulls.)
2. Each table can have multiple unique keys.
3. On some RDBMS A unique key automatically generates a non-clustered table index by default.

Read more about Unique Key:  Defining Unique Keys, Surrogate Keys, Alternate Key

Famous quotes containing the words unique and/or key:

    “The unique random blend
    Of families and fashions, there
    At last begin to loosen.”
    —Philip Larkin (1922–1986)

    “At the last, tenderly,
    From the walls of the powerful fortress’d house,
    From the clasp of the knitted locks, from the keep of the well-closed doors,
    Let me be wafted.

    Let me glide noiselessly forth;
    With the key of softness unlock the locks—with a whisper,
    Set ope the doors O soul.”
    —Walt Whitman (1819–1892)