替代多個「選擇」與環

Question

CREATE TABLE tab_1 (
    t1 decimal (10), 
    t2 decimal (10), 
    t3 decimal (10) 
); 

INSERT INTO tab_1 (t1, t2, t3) VALUES (1, -2, -5); 
INSERT INTO tab_1 (t1, t2, t3) VALUES (-3, 4, 6); 
INSERT INTO tab_1 (t1, t2, t3) VALUES (5, 1, 2); 


SELECT sum(t1) FROM tab_1 WHERE t1 > 0; 
SELECT sum(t2) FROM tab_1 WHERE t2 > 0; 
SELECT sum(t2) FROM tab_1 WHERE t3 > 0;` 

我有一個查詢像上面，我需要一個腳本，可以用for i=1:3

更換三select輸出必須是這樣的：

Q_total：

謝謝！

我使用MySQL工作臺6.3.7

Answer 1

您可以用INFORMATION_SCHEMA.COLUMNS的幫助和PREPARE statement

SET @sql := ''; 
SELECT 
GROUP_CONCAT('SELECT SUM(',COLUMN_NAME,') FROM tab_1 WHERE ',COLUMN_NAME, ' > 0' SEPARATOR ' UNION ALL ') INTO @sql 
FROM information_schema.COLUMNS 
WHERE TABLE_SCHEMA ='your_database_name' 
AND TABLE_NAME ='your_table_name'; 

PREPARE stmt FROM @sql; 
EXECUTE stmt; 
DEALLOCATE stmt; 

Answer 2

你必須使用Procedure這個

DELIMITER $$ 
CREATE PROCEDURE ABC() 

BEGIN 
    DECLARE a INT Default 1 ; 
    simple_loop: LOOP   
    SELECT sum(t@a) FROM tab_@a WHERE t@a > 0; 
    SET a=a+1; 
    IF a=4 THEN 
     LEAVE simple_loop; 
    END IF; 
END LOOP simple_loop; 
END $$ 

要調用存儲過程使用

CALL `ABC`() 

Answer 3

爲什麼你需要做到這一點一個函數？您正在查找的結果可以從單個查詢中獲得。

SELECT SUM(CASE WHEN t1 > 0 THEN t1 ELSE 0 END) AS t1Sum, 
     SUM(CASE WHEN t2 > 0 THEN t2 ELSE 0 END) AS t2Sum, 
     SUM(CASE WHEN t3 > 0 THEN t3 ELSE 0 END) AS t3Sum 
FROM tab_1