Altering columns in a table

Adding or changing columns to a table with the ALTER TABLE command.

• Add an age column of type int to the table cycling.cyclist_alt_stats.

  ALTER TABLE cycling.cyclist_alt_stats ADD age int;

  This creates the column metadata, adds the column to the table schema, and sets the value to NULL for all rows.

  Verify that the column was added with null values.

  SELECT id, age FROM cycling.cyclist_alt_stats LIMIT 3;

  The result set shows the first three rows.

   id                                   | age
  --------------------------------------+------
   e0953617-07eb-4c82-8f91-3b2757981625 | null
   a9e96714-2dd0-41f9-8bd0-557196a44ecf | null
   ed584e99-80f7-4b13-9a90-9dc5571e6821 | null
  
  (3 rows)

• Add a column favorite_color of varchar, and then change the data type of the same column to text.

  ALTER TABLE cycling.cyclist_alt_stats ADD favorite_color varchar;
  ALTER TABLE cycling.cyclist_alt_stats ALTER favorite_color TYPE text;

  Note: There are limitations on altering the data type of a column. The two data types, the original and the one changing to, must be compatible.