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The following statement creates a table named invoices which will not have any PRIMARY KEY. The following statement will create a table named ‘CITIES’ whose primary key is a combination of city_id and country_id.Įxample to ALTER TABLE for adding PRIMARY KEY after table creation. Example #2 – Multiple Columns PRIMARY KEY The country_id is the COUNTRIES table’s primary key, which used to identify the country in the COUNTRIES table uniquely. Let’s create a table named COUNTRIES using the CREATE TABLE statement in order to understand the examples. We can use the CONSTRAINT clause as follows to assign the name for the same:ĬONSTRAINT constraint_name PRIMARY KEY(column_name1, column_name2.) Examples to Implement Primary Key in PostgreSQL
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If we have a table named CITIES, then PostgreSQL creates the primary key constraint with the name cities_pkey for the same. PostgreSQL assigns table_name_pkey as the default name for the primary key constraint. If we don’t define the primary key constraint name explicitly then PostgreSQL assigns a default name to the primary key constraint. The PostgreSQL creates a unique B-TREE index on PRIMARY KEY columns if we have added PRIMARY KEY on the table using a column or a group of columns of a table. With the help of the ALTER TABLE statement, we can remove an existing primary key constraint of the table as follows:ĪLTER TABLE table_name DROP CONSTRAINT primary_key_constraint How does Primary Key work in PostgreSQL? We can achieve the same using an ALTER TABLE statement as follows:ĪLTER TABLE table ADD PRIMARY KEY (column1, column) We can add a primary key constraint for an existing table, which is rare. We can create a primary key constraint containing two or more columns as follows: We can add the primary key constraint to a table while creating the table itself using the CREATE TABLE statement.Ģ. Add the primary key while creating the table. Hadoop, Data Science, Statistics & othersġ.