CI如何在另一列查询

Question

+-----+-----+-------+ 
| PID | Qty | Price | 
+-----+-----+-------+ 
| 1 | 5 | 100 | 
| 2 | 10 | 500 | 
| 3 | 4 | 300 | 
+-----+-----+-------+ 

$this->db->select("SUM(qty) as total, price as last price"); 
$this->db->from('table'); 
$query = $this->db->get(); 
$result = $query->result(); 

现在因为有价格，上面的代码将返回尽可能多的行的选择和选择另一列的最后一排，

我想只返回一行哪里有总数量和价格的最后一个值

预期输出：

Array (
    [0] => stdClass Object 
     (
      [total] => 19 
      [last_price] => 300 
     ) 
) 

我有成千上万的数量和价格的行的表，但我想选择列数量的总和和上价格的最后价值，而不是数量和价格的所有行的总和，我只想要价格的最后一个价值如何编写我的选择查询？

预先感谢您。

Answer 1

你可以像下面： -

$this->db->select("SUM(qty) AS qty, (SELECT Price FROM <table name> ORDER BY PID DESC LIMIT 1) AS Price"); 
$this->db->from('table'); 

注： - 而不是<table name>在那里写下你的实际表名。同样要注意列名。

Answer 2

您可以使用此

SELECT SUM(qty) As qty, (SELECT Price FROM table price desc limit 1) AS price FROM table price dlimit 1

Answer 3

试试这个得到结果：

SELECT SUM(qty), a.* 
FROM products, 
(SELECT price FROM products 
ORDER BY pid DESC 
LIMIT 1) a;