如何在MySQL中使用蘭德函數與聯合使用

Question

我想結合3選擇語句，將選擇不同食物類別的不同食物名稱的結果。但是我的表格中有很多「foodItems」的例子。我需要爲每個選擇語句只選擇一個項目，並且我希望它隨機完成。我不太清楚如何實現，我試圖在每個select語句的末尾插入ORDER BY RAND() LIMIT 1，但MySQL不喜歡它。有人可以幫

SELECT foodName 
FROM food 
WHERE foodCategory_id = 1 OR 2 
UNION 
SELECT foodName 
FROM food 
WHERE foodCategory_id = 7 OR 8 OR 9 
UNION 
SELECT foodName 
FROM food 
WHERE foodCategory_id = 10 OR 11 

Answer 1

您可以創建一個外部SQL在FROM子句是某種臨時表是這樣的：

SELECT food_name from (
    SELECT foodName 
    FROM food 
    WHERE foodCategory_id = 1 OR 2 
    ORDER BY RAND() limit 1) a 
UNION 
SELECT food_name from (
    SELECT foodName 
    FROM food 
    WHERE foodCategory_id = 7 OR 8 OR 9 
    ORDER BY RAND() limit 1) b 
UNION 
SELECT food_name from (
    SELECT foodName 
    FROM food 
    WHERE foodCategory_id = 10 OR 11 
    ORDER BY RAND() limit 1) c  

Answer 2

SELECT foodname FROM food WHERE .. ORDER BY RAND() LIMIT 0,1; 

只需添加你想，無論WHERE條件。