如何合并2个检查相同标志列但值不同的查询

Question

I have 2 query which i used to fetch sum of values based on flag value

SELECT SUM(stock_deliveries.stockValue) AS stockValues1
FROM `stock_deliveries`
LEFT JOIN `delivery` ON `delivery`.`pk_deliveryId`  = `stock_deliveries`.`fk_deliveryId`
WHERE `stock_deliveries`.`fk_stockID` = '189'
AND `delivery`.`delivery_completed` = '1'

SELECT SUM(stock_deliveries.stockValue) AS stockValues2
FROM `stock_deliveries`
LEFT JOIN `delivery` ON `delivery`.`pk_deliveryId`  = `stock_deliveries`.`fk_deliveryId`
WHERE `stock_deliveries`.`fk_stockID` = '189'
AND `delivery`.`delivery_completed` = '0

Is it possible to merge this 2 query in single query ? thanks in advance.

Answer 1

Yes, you'd use conditional aggregation (ie CASE WHEN inside an aggregation function like SUM ):

select
  sum(case when d.delivery_completed = 0 then sd.stockvalue end) as stockvalues0,
  sum(case when d.delivery_completed = 1 then sd.stockvalue end) as stockvalues1
from stock_deliveries sd
left join delivery d on d.pk_deliveryid = sd.fk_deliveryid
where sd.fk_stockid = 189;

Answer 2

You can use a single query with the help of GROUP BY

SELECT SUM(stock_deliveries.stockValue) AS stockValues, `delivery`.`delivery_completed` as deliveryCompleted
FROM `stock_deliveries`
LEFT JOIN `delivery` ON `delivery`.`pk_deliveryId` =  `stock_deliveries`.`fk_deliveryId`
WHERE `stock_deliveries`.`fk_stockID` = '189'
GROUP BY `delivery`.`delivery_completed`;

Doing so you will have a row for every value of delivery_completed with the associated sum (if you need only 0 and 1 values you can add to the where clause and delivery.delivery_completed IN (0,1) ). Example:

stockValues    deliveryCompleted
       1000           0
        700           1

Answer 3

you can use "if" inside sum to check if you need the value in stockValues1 or stockValues0

SELECT SUM(IF(d.delivery_completed = 1, sd.stockValue, 0)) AS stockValues1, SUM(IF(d.delivery_completed = 0, sd.stockValue, 0)) AS stockValues2
FROM stock_deliveries sd
LEFT JOIN delivery d ON d.pk_deliveryId  = sd.fk_deliveryId
WHERE sd.fk_stockID = '189'
AND (d.delivery_completed = 1 OR d.delivery_completed = 0)

obviously if "delivery_completed" is only 1 or 0, you can omit the last AND in the query ;)

Edit: as Thorsten Kettner answered you can also use case-when syntax, with only one "case" they are substantially equivalent. The if syntax in this case is more concise, but if you have more options is more flexible, for instance:

SELECT CASE sometable 
       WHEN 'top' THEN 'high' 
       WHEN 'center' THEN 'medium' 
       ELSE 'low' 
       END AS position

Answer 4

您可以使用UNION ALL运算符保留2个结果行的逻辑，但现在它们处于相同结果中，而不是2个分隔行