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我想创建一个包含数据的表，但我希望其中一个列是另一个表中的数据（如外键），但我不需要这种数据库完整性，我只想获得表中的值b 如表 a 所示。

问题：有没有办法像我上面描述的那样创建局部视图？

提前致谢。

SQL 代码：

CREATE TABLE table1 (
data_column_1 int(10)
data_column_2 int(10)
data_column_3 int(10)
view_column_2 varchar(250)
/* from on table 2
   updated with a trigger? that reads data_column_2
   and based on the value in data_column_2, updates the value in view_column_2
   (like a vlookup like in excel)]
*/
view_column_3 varchar(250)
/* from on table 3
   updated with a trigger? that reads data_column_3
   and based on the value in data_column_3, updates the value in view_column_3
   (like a vlookup like in excel)
*/
)
4

1 回答 1

1

如果我理解正确，您只需要两个参考表和一个SELECTwith JOIN。您CREATE TABLE对三个表的语句可能如下所示

CREATE TABLE table1 (
    data_column_1 int(10),
    data_column_2 int(10),
    data_column_3 int(10)
);
CREATE TABLE table2 (
    data_column_2 int(10),
    view_column_2 varchar(250)
);
CREATE TABLE table3 (
    data_column_3 int,
    view_column_3 varchar(250)
);

假设我们有以下样本数据 

table 1
------------
10    1    3
20    2    2
30    3    1

table2
------------
1    Apple
2    Banana
3    Orange

table3
------------
1    Red
2    Green
3    Yellow

然后这SELECT会给你想要的

SELECT t1.data_column_1,
       t1.data_column_2,
       t1.data_column_3,
       t2.view_column_2,
       t3.view_column_3
  FROM table1 t1 LEFT JOIN
       table2 t2 ON t1.data_column_2 = t2.data_column_2 LEFT JOIN
       table3 t3 ON t1.data_column_3 = t3.data_column_3

我们LEFT JOIN假设并非 data_column_2 和 data_column_3 中的所有值都分别在 table2.view_column_2 和 table3.view_column3 中有参考值。如果您总是在参考表中有相应的值，或者您想从结果集中过滤掉那些没有它们的值，那么请INNER JOIN改用。

输出：

+---------------+---------------+---------------+---------------+---------------+
| data_column_1 | data_column_2 | data_column_3 | view_column_2 | view_column_3 |
+---------------+---------------+---------------+---------------+---------------+
|            10 |             1 |             3 | Apple         | Yellow        |
|            20 |             2 |             2 | Banana        | Green         |
|            30 |             3 |             1 | Orange        | Red           |
+---------------+---------------+---------------+---------------+---------------+

如果你愿意，你可以把它包在一个视图中

CREATE VIEW consolidated_table
AS
SELECT t1.data_column_1,
       t1.data_column_2,
       t1.data_column_3,
       t2.view_column_2,
       t3.view_column_3
  FROM table1 t1 LEFT JOIN
       table2 t2 ON t1.data_column_2 = t2.data_column_2 LEFT JOIN
       table3 t3 ON t1.data_column_3 = t3.data_column_3

然后像这样使用它

SELECT * 
  FROM consolidated_table
 WHERE data_column_1 < 20

输出：

+---------------+---------------+---------------+---------------+---------------+
| data_column_1 | data_column_2 | data_column_3 | view_column_2 | view_column_3 |
+---------------+---------------+---------------+---------------+---------------+
|            10 |             1 |             3 | Apple         | Yellow        |
+---------------+---------------+---------------+---------------+---------------+
于 2013-02-27T08:09:16.480 回答