Question

我有以下select语句，它计算值在连接表中出现的次数：

SELECT table1.idx, count(table1.idx) FROM 
(table2 INNER JOIN table1 ON table1.id=table2.id AND table2.value = 'target') 
GROUP BY table1.idx;

现在我想用这些结果更新第三个表，设置table3.idx = table1.idx的计数。我试过了

UPDATE table3 SET count_col=joined_table.c FROM 
(SELECT table1.idx, count(table1.idx) FROM 
   (table2 INNER JOIN table1 ON table1.id=table2.id AND table2.value = 'target') 
   GROUP BY table1.idx
) joined_table WHERE table3.idx = table1.idx;

根据modulo function的建议，并尝试了

UPDATE table3 SET count_col=(
    SELECT COUNT(table1.idx) 
    FROM (table1 INNER JOIN table2 ON table1.id=table2.id AND table2.value = 'target') 
    GROUP BY table1.idx 
WHERE table3.idx = table1.idx);

按How do I UPDATE from a SELECT in SQL Server?中的建议，但它们都不起作用。什么是正确的语法？

Answer 1

UPDATE table3 
JOIN 
(
  SELECT table1.idx, count(table1.idx) as cnt
  FROM table2 
  INNER JOIN table1 ON table1.id = table2.id 
                   AND table2.value = 'target'
  GROUP BY table1.idx
) joined_table ON table3.idx = joined_table.idx
SET count_col = joined_table.cnt

使用内部联接中的select count（）更新mysql

1 个答案: