MySql的更新不承認臨時表

Question

我有一個導致錯誤下面的查詢腳本：

SET @row_number = 0; 

Drop Table If Exists testtable2; 

Create Temporary Table testtable2 
SELECT 
    * 
FROM 
    (SELECT 
     row_names, (@row_number:=@row_number + 1) AS num, date_add(date_time, INTERVAL 1 MINUTE) AS date_time, meter, kw 
    FROM 
     testtable 
    WHERE 
     DAY(date_time) = 1 
      AND HOUR(date_time) = 2) AS testtable2 
WHERE 
    MOD(testtable2.num, 2) = 0; 

UPDATE testtable 
SET 
    testtable.date_time = testtable2.date_time 
WHERE 
    testtable.row_names = testtable2.row_names; 

錯誤說Error Code: 1054. Unknown column 'testtable2.row_names' in 'where clause'

我創建了一個包含列DATE_TIME但我更新的臨時表查詢無法識別該列是否存在。我可以運行像SELECT * FROM testtable2;並返回顯示該列確實是使用正確的標題生成的。爲什麼我的更新無法識別此列？

Answer 1

這是你update語句執行UPDATE：

UPDATE testtable 
SET testtable.date_time = testtable2.date_time 
WHERE testtable.row_names = testtable2.row_names; 

什麼是testtable？你還沒有定義。您創建了testtable2。如果你有testtable，那麼也許你想要一個join：

UPDATE testtable tt JOIN 
     testtable2 tt2 
     ON tt.row_names = tt2.row_names 
    SET tt.date_time = tt2.date_time; 

Answer 2

你實際上打算使用CREATE TABLE ... AS結構，但在你的情況下它是錯誤地形成的。它應該如下所示。

Create Temporary Table testtable2 AS 
SELECT 
    * 
FROM 
    (SELECT 
     row_names, (@row_number:=@row_number + 1) AS num, 
     date_add(date_time, INTERVAL 1 MINUTE) AS date_time, 
     meter, 
     kw 
    FROM 
     testtable 
    WHERE 
     DAY(date_time) = 1 
      AND HOUR(date_time) = 2) AS XXX <-- Here 
WHERE 
    MOD(testtable2.num, 2) = 0; 

問題在你的情況是，你的臨時表和內聯視圖別名是相同的。命名他們不同。請參閱編輯的查詢

---

您可以直接JOIN與內查詢，可以像

UPDATE testtable 
JOIN (
SELECT 
    * 
FROM 
    (SELECT 
     row_names, (@row_number:=@row_number + 1) AS num, date_add(date_time, INTERVAL 1 MINUTE) AS date_time, meter, kw 
    FROM 
     testtable 
    WHERE 
     DAY(date_time) = 1 
      AND HOUR(date_time) = 2) AS testtable2 
WHERE 
    MOD(testtable2.num, 2) = 0) xx ON testtable.row_names = xx.row_names 
SET 
    testtable.date_time = xx.date_time;