數據函數在子查詢中分組的項目

Question

我正在使用Postgresql來編寫一個查詢，該查詢每天計算差異值的總和並從其他表中獲得單價il_costs，我試圖用子查詢實現。下面整個查詢：

SELECT date(read.readed_at), 
     SUM(read.diff), 
     (SELECT water_unit 
     FROM il_costs 
     WHERE EXTRACT(MONTH FROM created_at) = EXTRACT(MONTH FROM date(read.readed_at)) 
      AND EXTRACT(YEAR FROM created_at) = EXTRACT(YEAR FROM date(read.readed_at))) 
FROM il_communicators_readings read 
GROUP BY date(read.readed_at) 
ORDER BY date(read.readed_at) ASC; 

我收到約未分組列的錯誤，但我使用date(read.readed_at)也分組功能：

ERROR: subquery uses ungrouped column "read.readed_at" from outer query 
LINE 1: ...(MONTH FROM created_at) = EXTRACT(MONTH FROM date(read.reade... 

Answer 1

您可以嘗試使用查詢作爲子查詢，並執行外部查詢相關子查詢：

SELECT mydate, s_diff, 
     (SELECT water_unit 
     FROM il_costs 
     WHERE EXTRACT(MONTH FROM created_at) = EXTRACT(MONTH FROM mydate) 
      AND EXTRACT(YEAR FROM created_at) = EXTRACT(YEAR FROM mydate)) 
FROM (
    SELECT date(read.readed_at) AS mydate, 
     SUM(read.diff) as s_diff 
    FROM il_communicators_readings read 
    GROUP BY date(read.readed_at)) AS t 
ORDER BY mydate ASC; 

Answer 2

問題沒有read.readed_at，它是在group by子查詢沒有。我不認爲這樣使用子查詢是個好主意。

試試這個：

SELECT date(read.readed_at), 
    SUM(read.diff), 
    costs.water_unit 
FROM il_communicators_readings read 
Left Join il_costs costs 
ON EXTRACT(MONTH FROM costs.created_at) = EXTRACT(MONTH FROM date(read.readed_at)) 
AND EXTRACT(YEAR FROM costs.created_at) = EXTRACT(YEAR FROM date(read.readed_at)) 
GROUP BY date(read.readed_at),costs.water_unit 
ORDER BY date(read.readed_at) ASC;