MySQL - >按條件選擇平均值和平均值

Question

在我的查詢中，我需要選擇四個值 - 某些日期的平均值，某個日期的平均值，總計數和計數。我的查詢現在只用於平均值和數量。是需要有兩個查詢還是隻能使用一個？

SELECT AVG(value) as average, 
COUNT(*) as noRates 
FROM `ratings` WHERE mid = 31 

什麼，我希望是像

SELECT AVG(value) as average, 
COUNT(*) as noRates, 
AVG(value WHERE datecolumn = '2014-10-17') as averageToday, 
COUNT(* WHERE datecolumn = '2014-10-17') as noRatesToday 
FROM `ratings` 
WHERE mid = 31 

Answer 1

對於您可以使用情況和條件數，您可以直接把你的表達和表現像作爲計數功能有條件的平均

SELECT 
AVG(`value`) AS average, 
COUNT(*) AS noRates, 
AVG(CASE WHEN datecolumn = '2014-10-17' THEN `value` ELSE 0 END) AS averageToday, 
SUM(datecolumn = '2014-10-17') AS noRatesToday 
FROM `ratings` 
WHERE `mid` = 31