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3.5 Modifying Tables

When you create a table and you realize that you made a mistake, or the requirements of the application change, then you can drop the table and create it again. But this is not a convenient option if the table is already filled with data, or if the table is referenced by other database objects (for instance a foreign key constraint). Therefore PostgreSQL provides a family of commands to make modifications to existing tables. Note that this is conceptually distinct from altering the data contained in the table: here we are interested in altering the definition, or structure, of the table.

You can

• Add columns,
• Remove columns,
• Add constraints,
• Remove constraints,
• Change default values,
• Change column data types,
• Rename columns,
• Rename tables.

All these actions are performed using the ALTER TABLE command, q.v. for details beyond those given here.