行之間的Mysql差異

我想通過給定的以下數據從2行得到汽車的價格差異。我想價格。減去前柱（200-100），（300-200）等數據行之間的Mysql差異

我的表：

我曾嘗試

select t1.row_num1,t1.car_name 
from 
(
    select (@row_num := @row_num +1) as row_num1 ,(select @row_num =0) r1, car_name,price 
    from car 
)t1

我知道我沒有id column.hence我正在生成row_number。現在我遇到了問題，自我加入這張表，並得到不同。你的幫助是可觀的。

來源

2016-03-04 user3172982

請解釋輸出位 – 1000111

有差異被反對的價格計算與其餘的第一輛車？ – 1000111

讓我更新我的問題......這將很容易理解 – user3172982

雖然你的輸出顯得撲朔迷離。然而我給了以下的答案：

SOLUTION #1

SELECT 
carsTable1.car_name, 
carsTable1.price, 
CASE WHEN ABS(carsTable1.price - (SELECT price FROM cars WHERE car_name='car 2')) = 0 THEN NULL ELSE 
     ABS(carsTable1.price - (SELECT price FROM cars WHERE car_name='car 2')) END diff 
FROM 
(SELECT 
    @rn := @rn + 1 row_number, 
    cars.car_name, 
    cars.price 
FROM cars, (SELECT @rn := 0) var 
) carsTable1;

Demo Here

樣品輸入：

car_name price 

car 1  100 

car 2  200 

car 3  300

樣本輸出：

car_name price  diff 

    car 1  100  100 

    car 2  200  NULL 

    car 3  300  100

注：的car 2價格與汽車的其餘部分的價格進行比較。所以結果顯示null爲car 2，因爲它是參考車。

如果我誤解了你的要求，那麼它一定是：你想連續行即之間的價格差異(No car,car1),(car1,car2), (car2,car3), (car3,car4)....

所以在這種情況下，你可以通過下面的查詢：

SOLUTION #2

SELECT 
car_name, 
cars.price, 
CASE WHEN @currentPrice = 0 THEN NULL ELSE ABS(cars.price - @currentPrice) END AS diff, 
@currentPrice := price 
FROM cars ,(SELECT @currentPrice := 0) var 
ORDER BY car_name

SQL FIDDLE BASED ON THIS QUERY

如果你想omit the fourth column：

SELECT 
t.car_name, 
t.price, 
t.diff 
FROM 
(
    SELECT 
    car_name, 
    cars.price, 
    CASE WHEN @currentPrice = 0 THEN NULL ELSE (cars.price - @currentPrice) END AS diff, 
    @currentPrice := price 
    FROM cars ,(SELECT @currentPrice := 0) var 
    ORDER BY car_name) t

SQL FIDDLE BASED ON THIS QUERY

來源

2016-03-04 10:41:30 1000111

如果符合您的要求，請您檢查一下嗎？ @ user3172982 – 1000111

嘗試這個

set @next_row_price := null; 
SELECT car_name , price, diff FROM(
    SELECT car_name,price,(@next_row_price - price) * -1 AS diff, 
    IF(@next_row_price IS NULL, @next_row_price := price, 0) , 
    IF(@next_row_price IS NOT NULL, @next_row_price := price, 0) 
FROM car 
) AS TEMP;

SQLFiddle

來源

2016-03-04 10:41:58

無論如何不需要設置它爲NULL的變量。 – Mihai

將'ORDER BY car_name'添加到派生表中，否則結果將基於插入順序... – dnoeth

在他的願望輸出中，沒有'order by'的要求 –

試試這個： -

CREATE TABLE #TempTable (rownum INT, price int, car_name VARCHAR(256)); 
INSERT INTO #TempTable (rownum, price, car_name) 
SELECT 
rownum = ROW_NUMBER() OVER (ORDER BY c.car_id), 
c.price, 
c.car_name 
FROM car c; 
SELECT 
    NEX.car_name + '-' + TT.car_name, 
    (nex.price - tt.price) AS Differences 
    FROM #TempTable TT 
LEFT JOIN #TempTable prev ON prev.rownum = TT.rownum - 1 
LEFT JOIN #TempTable nex ON nex.rownum = TT.rownum + 1;

來源

2016-03-04 11:54:02 Amee

行之間的Mysql差異

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