教科书MergeSort在SQL中的实现(Postgres)

CREATE OR REPLACE FUNCTION merge_sort(input_table_name text) RETURNS SETOF record AS $$
DECLARE
    sorted_table_name text := 'sorted_' || input_table_name;
BEGIN
    -- 实现MergeSort算法的逻辑
    -- ...
END;
$$ LANGUAGE plpgsql;

EXECUTE 'CREATE TEMPORARY TABLE ' || sorted_table_name || ' AS SELECT * FROM ' || input_table_name || ' LIMIT 0';

CREATE OR REPLACE FUNCTION merge_sort(input_table_name text) RETURNS SETOF record AS $$
DECLARE
    sorted_table_name text := 'sorted_' || input_table_name;
BEGIN
    EXECUTE 'CREATE TEMPORARY TABLE ' || sorted_table_name || ' AS SELECT * FROM ' || input_table_name || ' LIMIT 0';

    EXECUTE 'INSERT INTO ' || sorted_table_name || ' SELECT * FROM ' || input_table_name || ' WHERE 1=0';

    EXECUTE 'INSERT INTO ' || sorted_table_name || ' SELECT * FROM ' || merge_sort('first_half_' || input_table_name) || ' UNION ALL SELECT * FROM ' || merge_sort('second_half_' || input_table_name);

    EXECUTE 'INSERT INTO ' || input_table_name || ' SELECT * FROM ' || sorted_table_name;

    EXECUTE 'DROP TABLE ' || sorted_table_name;

    RETURN QUERY EXECUTE 'SELECT * FROM ' || input_table_name;
END;
$$ LANGUAGE plpgsql;