How do I ALTER a PostgreSQL table and make a column unique?

SqlPostgresqlUnique Constraint

Sql Problem Overview

I have a table in PostgreSQL where the schema looks like this:

CREATE TABLE "foo_table" (
    "id" serial NOT NULL PRIMARY KEY,
    "permalink" varchar(200) NOT NULL,
    "text" varchar(512) NOT NULL,
    "timestamp" timestamp with time zone NOT NULL
)

Now I want to make the permalink unique across the table by ALTER-ing the table.

Sql Solutions

Solution 1 - Sql

I figured it out from the PostgreSQL docs, the exact syntax is:

ALTER TABLE the_table ADD CONSTRAINT constraint_name UNIQUE (thecolumn);

Thanks Fred.

Solution 2 - Sql

Or, have the DB automatically assign a constraint name using:

ALTER TABLE foo ADD UNIQUE (thecolumn);

Solution 3 - Sql

it's also possible to create a unique constraint of more than 1 column:

ALTER TABLE the_table 
    ADD CONSTRAINT constraint_name UNIQUE (column1, column2);
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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionBaishampayan GhoseView Question on Stackoverflow
Solution 1 - SqlBaishampayan GhoseView Answer on Stackoverflow
Solution 2 - SqlClint PachlView Answer on Stackoverflow
Solution 3 - SqlStefanView Answer on Stackoverflow