Syntax: ALTER TABLE table_name ALTER COLUMN column_name [SET DATA] TYPE new_data_type;
Let’s analyze the above syntax:
- First, specify the name of the table to which the column you want to change belongs in the ALTER TABLE clause.
- Second, give the name of column whose data type will be changed in the ALTER COLUMN clause.
- Third, provide the new data type for the column after the TYPE keyword. It is possible to use either SET DATA TYPE or TYPE.
Let’s create a table (say, assets) and insert a few rows into it for the demonstration using the below statement:
CREATE TABLE assets ( id serial PRIMARY KEY, name TEXT NOT NULL, asset_no VARCHAR NOT NULL, description TEXT, LOCATION TEXT, acquired_date DATE NOT NULL ); INSERT INTO assets ( NAME, asset_no, location, acquired_date ) VALUES ( 'Server', '10001', 'Server room', '2020-01-01' ), ( 'UPS', '10002', 'Server room', '2020-05-16' );
Now we will change the data type of the
name column to VARCHAR, using the below statement:
ALTER TABLE assets ALTER COLUMN name TYPE VARCHAR;
Now we change the data type of description and location columns from TEXT to VARCHAR using the below statement:
ALTER TABLE assets ALTER COLUMN location TYPE VARCHAR, ALTER COLUMN description TYPE VARCHAR;
Now we check the table for the changes made using the below statement:
SELECT * FROM assets;
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