Sql用兩個列左加入過濾器

更新：這已解決，我正在發出語法錯誤。Sql用兩個列左加入過濾器

我可以連接並過濾左連接中的兩列嗎？例如：

tbl_people 
id food  side  value 
a  pizza fries 10 
b  pizza shake  2 
c  burger fries 3 

tbl_sides 
food  side 
pizza fries 
burger fries

然後利用SQL：

SELECT 
    id, food, side, value 
FROM 
    tbl_people AS people 
LEFT JOIN 
    tbl_sides AS sides ON sides.food = people.food 
    AND sides.side = people.side

我可以添加一個標誌，以便我能確定的食品對是否是在加入或如果它是NULL？我不想內部加入，因爲我需要計算每個人的總食量/人數，並且還要匹配每個人的食物/人對。我試過：

SELECT 
    id, food, side, value, 
    CASE WHEN 
    side.side IS NOT NULL 
    AND side.food IS NOT NULL 
    THEN 1 
    ELSE 0 
    END AS match_flag 
FROM 
    tbl_people AS people 
LEFT JOIN 
    tbl_sides AS sides ON sides.food = people.food 
    AND sides.side = people.side

但它不工作。基本上我只需要標記何時未加入連接但我遇到問題。

來源

2013-09-24 Jeffrey Kramer

我想你想要的是這樣的：

SELECT 
    id, food, side, value, 
    CASE WHEN 
    side.side = people.side 
    THEN 1 
    ELSE 0 
    END AS match_flag 
FROM 
    tbl_people AS people 
LEFT JOIN 
    tbl_sides AS sides ON people.food = sides.food

來源

2013-09-24 16:18:25

哦，你說的沒錯，我是過於複雜，我很抱歉。 –

隨着MySQL的表達式，將返回一個true /假1/0，尋找布爾輸出時，作爲速記CASE聲明。

這將致力於標誌不匹配，用1：

SELECT 
    people.id, people.food, people.side, people.value 
    ,sides.food IS NULL AS match_flag 
FROM 
    tbl_people AS people 
LEFT JOIN tbl_sides AS sides 
    ON sides.food = people.food 
    AND sides.side = people.side

演示：SQL Fiddle

或者這標誌不匹配的爲0：

SELECT 
    people.id, people.food, people.side, people.value 
    ,COALESCE(sides.food = people.food,0) AS match_flag 
FROM 
    tbl_people AS people 
LEFT JOIN tbl_sides AS sides 
    ON sides.food = people.food 
    AND sides.side = people.side

演示： SQL Fiddle

來源

2013-09-24 16:20:50

嘗試在連接前標記空值

SELECT 
    people.id, people.food, people.side, people.value, nvl(sides.side, 'NOT JOINED') 
FROM 
    tbl_people AS people 
LEFT JOIN 
    (select food, nvl(side, 'SOME NULL') as side from tbl_sides) AS sides 
ON sides.food = people.food 
AND sides.side = people.side

來源

2013-09-24 16:26:08

它返回1時，表達式爲NULL，否則返回0

http://sqlfiddle.com/#!2/cadbdd/15/0

SELECT *, ISNULL(sides.food) AS match_flag 
FROM 
    tbl_people AS people 
LEFT JOIN 
    tbl_sides AS sides ON sides.food = people.food 
    AND sides.side = people.side

來源

2013-09-24 16:35:55 sqlint

Sql用兩個列左加入過濾器

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