Question

我有一张这样的表：

recordid customerid产品ID计数
1 2 12 3
   2 4 10 1
   3 2 3 3
   4 3 12 2
   5 3 10 2
   6 2 7 3
   7 5 3 1
   8 ....    9 ....

我想要一个更新查询，它会计算每个客户ID的出现次数，并更新最初为空的count列。最终结果应如上所述列名是虚拟的，我的实际表是不同的。它有数百万行的数据。查询应该很快我尝试了查询，但它被卡住了...... update tablename，（select count（recordid）as count，customerid from tablename group by customerid）as temp set count = temp.count where customerid = temp.customerid

Answer 1

您可以在JOIN中使用UPDATE。

试试这个：

UPDATE TableName A
JOIN 
(SELECT customerid,Count(customerid) as cnt
FROM TableName
GROUP BY customerid) as B ON A.customerid= B.customerid
SET A.count = B.cnt

Answer 2

这看不对：

update tablename, (select count(recordid) as count,customerid from tablename group by customerid) as temp set count=temp.count where customerid=temp.customerid

为什么update tablename之后会出现逗号：

update tablename,

我也在重新格式化以提高可读性：

UPDATE tablename (
  SELECT count(recordid) AS count, customerid
  FROM tablename GROUP BY customerid
) as temp
SET count=temp.count
WHERE customerid = temp.customerid

使用MySQL服务器中同一表中其他列的计数更新表的列

2 个答案: