来自2个表的MySQL SUM值和JOIN

问题描述：

我有两个表，table2和table3都可能包含table1中key的金额.

I have two tables and both table2 and table3 may contain an amount for the key from table1.

我想总结这些值并将它们表示为amount.

I would like to sum up these values and represent them as amount.

SELECT table1.mg_key
     , table1.mg_name
     , table1.time
     , table2.mg_amount + table3.mg_amount amount
     , table2.mg_key + table.mg_key
  FROM table
  LEFT 
  JOIN table2
     , table3 
    ON table1.mg_key = key 
   AND key = amount

它不起作用，所以我可能做错了什么?

It doesn't work, so Im probably doing something wrong?

答

http://sqlfiddle.com/#!9/65dca/1/0

SELECT   
table1.mg_key, table1.mg_name, table1.time,
IFNULL(table2.mg_amount,0) + IFNULL(table3.mg_amount,0) as amount
FROM table1
LEFT JOIN table2 ON table1.mg_key = table2.mg_key
LEFT JOIN table3 ON table1.mg_key = table3.mg_key;

如果这不能回答您的问题，请创建 SQL小提琴以帮助我们更好地理解.

If this does not answer your question, please create a SQL Fiddle to help us better understand.

来自2个表的MySQL SUM值和JOIN

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