函數在postgres中返回多行，並返回一些空值

Question

我在函數postgress方法中沒有什麼問題。 我有功能：

CREATE OR REPLACE FUNCTION test(
    x integer, 
    y character varying, 
    z character varying 
) 
RETURNS TABLE(x1 int, y1 varchar,n1 varchar,z1 varchar) AS 
$BODY$ 
BEGIN 
    RETURN QUERY 
SELECT x,y,null,z FROM example_tab    
END; 
$BODY$ 
    LANGUAGE plpgsql VOLATILE 
    COST 100 
    ROWS 1000; 

當我執行這個功能我把錯誤：

Error: Returned type unknown does not match expected type character varying in column 3. 

SELECT * FROM test(694531020,'t'::varchar,'t'::varchar) 

我應該怎麼做才能正確運行此查詢，並執行該功能???

Answer 1

應明確指定數據類型爲空，如：

CREATE OR REPLACE FUNCTION test(
    x integer, 
    y character varying, 
    z character varying 
) 
RETURNS TABLE(x1 int, y1 varchar,n1 varchar,z1 varchar) AS 
$BODY$ 
BEGIN 
    RETURN QUERY 
SELECT x,y,null::varchar,z FROM example_tab    
END; 
$BODY$ 
    LANGUAGE plpgsql VOLATILE 
    COST 100 
    ROWS 1000;