[PostgreSQL] Ensure Uniqueness in Postgres

Change existing table, modify one field to be unique:

<span style="color: #0000ff;">ALTER</span> <span style="color: #0000ff;">TABLE</span> directors <span style="color: #0000ff;">ADD</span> <span style="color: #0000ff;">CONSTRAINT</span> directors_name_unique <span style="color: #0000ff;">UNIQUE</span>(name)

So now if we trying to insert the duplicate rows it will report error:

<span style="color: #0000ff;">INSERT</span> <span style="color: #0000ff;">INTO</span> directors (name) <span style="color: #0000ff;">VALUES</span> (<span style="color: #ff0000;">‘</span><span style="color: #ff0000;">Quintin Tarantino</span><span style="color: #ff0000;">‘</span>), (<span style="color: #ff0000;">‘</span><span style="color: #ff0000;">Quintin Tarantino</span><span style="color: #ff0000;">‘</span>) ;

Sometime, the unique constraint can be a combination of mulit fields:

<span style="color: #0000ff;">ALTER</span> <span style="color: #0000ff;">TABLE</span> movies <span style="color: #0000ff;">ADD</span> <span style="color: #0000ff;">CONSTRAINT</span> unique_title_and_release <span style="color: #0000ff;">UNIQUE</span>(title, release<span style="color: #808080;">-</span>date)

[PostgreSQL] Ensure Uniqueness in Postgres

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