MYSQL：同一语句中的 SELECT 和 UPDATE 不起作用 - 1064 错误

Question

I have an UPDATE and SELECT statement working in SQL however I am unable to replicate the same outcome in MYSQL.

I have a table (TBL1) with, say 4 columns:-

col1: registration (VARCHAR)

col2: date

col3: oldest date flag (values Y or blank)

col4: index (priamry key - auto-increment).

An ongoing process continues to add registrations and dates to the table. After a batch of additions any col3 'Y' flags will be removed and then an update process will set the col3 value = 'Y' for each the row where the registration has the oldest date.

Here is the SQL code, this works as expected after an earlier process removes any previous col3 'Y' values;-

UPDATE T1

SET T1.Col3 = 'Y'   
SELECT FROM TBL1 AS T1  
INNER JOIN (  SELECT Col1 AS REG, MIN(Col2) AS MINDATE  
              FROM TBL1  
              GROUP BY Col1) AS T2  
              ON T1.Col1 = T2.REG and T1.Col2 = T2.MINDATE         

The result correctly recognises for each unique registration the oldest date and sets 'Y' in col3.

I need to replicate this process in MYSQL but after much effort I can't find a way to do this?

Answer 1

If you are just looking for the same logic, but with MySQL's update join syntax, then try this:

UPDATE TBL1 T1
INNER JOIN
(
    SELECT Col1 AS REG, MIN(Col2) AS MINDATE
    FROM TBL1
    GROUP BY Col1
) AS T2
    ON T1.Col1 = T2.REG and T1.Col2 = T2.MINDATE
SET T1.Col3 = 'Y';