Question

我遇到了从MySQL数据库中选择数据的问题。

例如，我有一个包含以下列的表格＆amp;表：

Table name: farming

id | animal | amount | food
----------------------------
1  |   Cow  |    10  | Grass
12 |  Sheep |    19  | Grass
23 |  Lion  |     1  | Everything
29 |  Lamb  |     3  | Grass
102|   Pig  |     8  | Everything
...

我希望从与所选amount的{{1}}类型相匹配的所有行中获取food。

E.g。如果我选择id，则会从id: 102

的所有行中获得amount

food = 'Everything' //这应该从SELECT amount FROM farming WHERE food = '".$_GET['food']."' **IS THE SAME TYPE AS IT IS IN** id = '1'";中选择10，19和3（因为amount的食物类型是{{1}所以它应该从foodtype = grass的所有行中选择id = 1。

**是我遇到问题的地方，我尝试了各种各样的陈述，似乎无法让它发挥作用。

Answer 1

你可以使用group by子句来汇总所有来自金额列的食物值=＆＃39; Grass＆＃39;

SELECT SUM(amount) ammount FROM farming 
      WHERE food = (select food FROM farming where id = 102) 
      GROUP BY food

Answer 2

这应该可以解决问题

select  amount
from    farming
where   food = (
            select  food
            from    farming
            where   id = 1
        )

复杂的SELECT MySQL语句

2 个答案: