Question

所以我一直在努力让mySQL查询适用于我拥有的大型数据库。我有（假设）两个表Table_One和Table_Two。 Table_One有三列Type，Anima和TestID，Table_Two有两列Test_Name和Test_ID。值的示例如下：

           TABLE_ONE


Type             Animal        TestID       
-----------------------------------------
Mammal             Goat           1
Fish               Cod            1
Bird               Chicken        1
Reptile            Snake          1
Bird               Crow           2
Mammal             Cow            2
Bird               Ostrich        3

Table_Two
Test_name         TestID       
-------------------------
Test_1              1
Test_1              1
Test_1              1
Test_1              1
Test_2              2
Test_2              2
Test_3              3

在Table_One中，所有类型都在一列之下，所有类型（哺乳动物，鱼类，鸟类，爬行动物）的值都在另一列（动物）之下。 Table_One和Two可以通过Test_ID

链接

我正在尝试创建一个如下所示的表：

Test_Name      Bird      Reptile      Mammal          Fish
-----------------------------------------------------------------
Test_1         Chicken    Snake        Goat            Cod
Test_2         Crow                    Cow
Test_3         Ostrich

这应该是我的决赛桌。我目前使用的方法是创建Table_One的多个实例并使用连接来形成此最终表。所以专栏Bird，Reptile，Mammal和Fish都来自Table_one的不同副本。

例如

Select
Test_Name As 'Test Case Name',
Table_Bird.Animal AS 'Birds',
Table_Mammal.Animal AS 'Mammal',
Table_Reptile.Animal AS 'Reptile,
Table_Fish.Animal AS 'Fish'
From Table_One
INNER JOIN TABLE_Two AS Table_Bird
On Table_One.TestID = Table_Bird.TestID
INNER JOIN TABLE_Two AS Table_Mammal
On Table_One.TestID = Table_Mammal.TestID
INNER JOIN TABLE_Two AS Table_Reptile
On Table_One.TestID = Table_Reptile.TestID
INNER JOIN TABLE_Two AS Table_Fish
On Table_One.TestID = Table_Fish.TestID
Where Table_Bird.Type LIKE 'Birds'
AND Table_Mammal.Type LIKE 'Mammals'
AND Table_Reptile.Type LIKE 'Reptiles'
AND Table_Fish.Type LIKE 'Fish'

此查询的问题是它仅适用于Birds，Mammals，Reptiles和Fish的所有条目都有一定价值的情况。如果一个字段为Test_Two或Test_Three为空，则它不会返回该记录。我在WHERE子句中使用Or代替And，但是它也没有用。

如果有人能指出我正确的方向，我真的很感激。

Answer 1

尝试将INNER JOIN语句替换为LEFT JOIN。

Answer 2

您可以尝试将您移动到JOIN条件并将其设为LEFT JOIN而不是INNER JOIN - 就像这样：

Select
    Test_Name As 'Test Case Name',
    Table_Bird.Animal AS 'Birds',
    Table_Mammal.Animal AS 'Mammal',
    Table_Reptile.Animal AS 'Reptile,
    Table_Fish.Animal AS 'Fish'
From Table_One
LEFT JOIN TABLE_Two AS Table_Bird ON Table_One.TestID = Table_Bird.TestID AND Table_Bird.Type LIKE 'Birds'
LEFT JOIN TABLE_Two AS Table_Mammal ON Table_One.TestID = Table_Mammal.TestID AND Table_Mammal.Type LIKE 'Mammals'
LEFT JOIN TABLE_Two AS Table_Reptile ON Table_One.TestID = Table_Reptile.TestID AND Table_Reptile.Type LIKE 'Reptiles'
LEFT JOIN TABLE_Two AS Table_Fish ON Table_One.TestID = Table_Fish.TestID AND Table_Fish.Type LIKE 'Fish'

如何将一个表中两列的数据拆分为结果表的多个列

2 个答案: