Question

I have PostgreSQL table with several boolean columns, currently containing only true or null. I want to do the following for all of them:

1. Add a default value of false
2. Change all null values to false
3. Add a not null constraint

ie.:

-- for each column specified:
update my_table set my_column = 'f' where my_column is null;
alter table my_table alter column my_column set default 'f';
alter table my_table alter column my_column set not null; 

Is there a feature of psql (or standard SQL) that will iterate over a specified list of columns and apply a sequence of operations to each one?

Answer 1

This will do, needs version 8.4 or higher because of the VARIADIC.

CREATE OR REPLACE FUNCTION setdefaults(
    IN _tname TEXT,     -- tablename to alter
    VARIADIC _cname TEXT[]  -- all columnnames to alter
) 
RETURNS boolean 
LANGUAGE plpgsql 
AS
$$
DECLARE
    row record;
BEGIN   
    FOR row IN SELECT unnest(_cname) AS colname LOOP
        EXECUTE 'ALTER TABLE ' || quote_ident(_tname) || ' ALTER COLUMN ' || quote_ident(row.colname) || ' SET DEFAULT false;';
        EXECUTE 'UPDATE ' || quote_ident(_tname) || ' SET ' || quote_ident(row.colname) || ' = DEFAULT WHERE ' || quote_ident(row.colname) || ' IS NULL;';
        EXECUTE 'ALTER TABLE ' || quote_ident(_tname) || ' ALTER COLUMN ' || quote_ident(row.colname) || ' SET NOT NULL;';
    END LOOP;

    RETURN TRUE;
END;
$$;

SELECT setdefaults('foo', 'x','y','z'); -- alter table "foo"