Php, MySql 从两个表求和

Question

我正在努力使这个查询工作:

SELECT 
  IFNULL(SUM(days), 0) AS days 
FROM
  `table_days` 
WHERE task = 1 
GROUP BY task 
UNION
ALL 
SELECT 
  IFNULL(SUM(total), 0) AS total 
FROM
  `table_total` 
WHERE task = 1 
GROUP BY task ;

我有两个表:

1. table_days

    id      task    days    
    ==========================
    1       1       3.00
    2       1       2.00


2. table_total
    id      task    total   
    ==========================
    1       3       0.00

上面的查询部分有效，结果是:

stdClass Object
(
    [days] => 5.00
)

但即使没有找到记录，我也想从第二个表中获取结果。有点像

stdClass Object
(
    [days] => 5.00
    [total] => 0.00
)

Answer 1

试试这个查询

SELECT 
  IFNULL(SUM(days), 0) AS days 
FROM
  `table_days` 
WHERE task = 1 
GROUP BY task 
UNION
ALL 
SELECT 
  SUM(case when task = 1 then IFNULL(total,0) else 0 end) AS total 
FROM
  `table_total` 
GROUP BY task ;