In PostgreSQL, you can create a permanent alias, often referred to as a synonym or table alias, for a table or column using views or table inheritance. Both views and table inheritance allow you to create an alternative name for an existing table or column without physically duplicating the data.

  1. Using Views: A view is a virtual table based on the result of a SELECT query. It allows you to encapsulate complex queries and present them as simple tables. You can create a view that represents the original table with a different name.

    Example for a table named "original_table" and a column named "original_column":

    sql
    -- Create a view as an alias for the table CREATE OR REPLACE VIEW alias_table AS SELECT * FROM original_table; -- Create a view as an alias for the column CREATE OR REPLACE VIEW alias_column AS SELECT original_column AS alias_column FROM original_table;

    Now, you can use the views "alias_table" and "alias_column" in your queries as if they were real tables or columns.

  2. Using Table Inheritance: Table inheritance is a feature in PostgreSQL that allows you to create child tables that inherit columns and properties from a parent table. You can create a child table with a different name, effectively acting as a permanent alias.

    Example:

    sql
    -- Create the parent table CREATE TABLE original_table ( id SERIAL PRIMARY KEY, name TEXT, age INTEGER ); -- Create the child table as an alias CREATE TABLE alias_table () INHERITS (original_table); -- Create a trigger to direct insert/update/delete operations to the parent table CREATE OR REPLACE FUNCTION trigger_alias_table() RETURNS TRIGGER AS $$ BEGIN IF (TG_OP = 'INSERT') THEN INSERT INTO original_table VALUES (NEW.*); RETURN NEW; ELSIF (TG_OP = 'UPDATE') THEN UPDATE original_table SET (name, age) = (NEW.name, NEW.age) WHERE id = NEW.id; RETURN NEW; ELSIF (TG_OP = 'DELETE') THEN DELETE FROM original_table WHERE id = OLD.id; RETURN OLD; END IF; END; $$ LANGUAGE plpgsql; CREATE TRIGGER alias_table_trigger BEFORE INSERT OR UPDATE OR DELETE ON alias_table FOR EACH ROW EXECUTE FUNCTION trigger_alias_table();

    Now, you can interact with "alias_table" as if it were a separate table, but any operations (insert, update, delete) on "alias_table" will be directed to the "original_table" through the trigger.

Both views and table inheritance provide ways to create permanent aliases for tables and columns in PostgreSQL. The choice between using views or table inheritance depends on your specific use case and requirements. Views are more commonly used for simple aliasing, while table inheritance might be suitable for more complex scenarios.

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