SQL更新和增量列使用同一表中的子查詢

Question

這是my fiddle。我查詢：

update foos 
set foo_id = ((SELECT max_foo_id FROM (SELECT MAX(foo_id) AS max_foo_id FROM foos) AS temp_foos) + 1) 
where foo_id is null; 

產生的foo_ids值1, 2, 2, 2（子查詢只運行一次？），但我想它給我1, 2, 3, 4

Answer 1

這個怎麼樣？

UPDATE foos a 
     INNER JOIN 
     (
      SELECT a.bar_ID, 
        @rn := @rn + 1 row_Num 
      FROM foos a,(SELECT @rn := (SELECT MAX(foo_ID) FROM foos)) b 
      WHERE a.foo_ID IS NULL 
     ) b ON a.bar_ID = b.bar_ID 
SET  a.foo_id = b.row_Num 

• SQLFiddle Demo

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UPDATE 1

• SQLFiddle Demo (with ORDER BY clause)