Primary key for multiple column in PostgreSQL?

Solution 1:

There can only be one primary key per table - as indicated by the word "primary".
You can have additional UNIQUE columns like:

CREATE TABLE test(
   sl_no int PRIMARY KEY,  -- NOT NULL due to PK
   emp_id int UNIQUE NOT NULL,
   emp_name text,
   emp_addr text
);

Columns that are (part of) the PRIMARY KEY are marked NOT NULL automatically.

Or use a table constraint instead of a column constraint to create a single multicolumn primary key. This is semantically different from the above: Now, only the combination of both columns must be unique, each column can hold duplicates on its own.

CREATE TABLE test(
   sl_no int,     -- NOT NULL due to PK below
   emp_id int ,   -- NOT NULL due to PK below
   emp_name text,
   emp_addr text,
   PRIMARY KEY (sl_no, emp_id)
);

Multicolumn UNIQUE constraints are possible, too.

Aside: Don't use CaMeL-case identifiers in Postgres. Use legal, lower-case identifiers so you never have to use double-quotes. Makes your life easier. See:

Are PostgreSQL column names case-sensitive?

Primary key for multiple column in PostgreSQL?

Solution 1:

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