def add_not_null(db, col):

    table = col.table

    col = sql_gen.to_name_only_col(col)

    run_query(db, 'ALTER TABLE '+table.to_str(db)+' ALTER COLUMN '

        +col.to_str(db)+' SET NOT NULL', cacheable=True)

def add_index_col(db, col, suffix, expr, nullable=True):

    if col.index_col != None: return # already has index col

    new_col = sql_gen.suffixed_col(col, suffix)

    new_typed_col = sql_gen.TypedCol(new_col.name, db.col_info(col).type)

    add_col(db, col.table, new_typed_col)

    update(db, col.table, [(new_col, expr)])

    if not nullable: add_not_null(db, new_col)

    add_index(db, new_col)

    col.index_col = new_col

def ensure_not_null(db, col):

    '''For params, see sql_gen.ensure_not_null()'''

    expr = sql_gen.ensure_not_null(db, col)

    # If nullable column in a temp table, add separate column instead

    if sql_gen.is_temp_col(col) and isinstance(expr, sql_gen.EnsureNotNull):

        add_index_col(db, col, '::NOT NULL', expr, nullable=False)

        expr = col.index_col

    return expr