MySQL组合了两列并添加到一个新列中

Question

我有一个MySQL表的以下结构:

+----------------+----------------+----------+
|    zipcode     |      city      |   state  |
+----------------+----------------+----------+
|     10954      |     Nanuet     |    NY    |
+----------------+----------------+----------+

我想将上面的3列组合成一列,如下所示:

+---------------------+
|      combined       |
+---------------------+
| 10954 - Nanuet, NY  |
+---------------------+

我想将这个"组合"列添加到表的末尾,而不会破坏原来的3个字段.

Answer 1

创建列:

ALTER TABLE yourtable ADD COLUMN combined VARCHAR(50);

更新当前值:

UPDATE yourtable SET combined = CONCAT(zipcode, ' - ', city, ', ', state);

自动更新所有未来值:

CREATE TRIGGER insert_trigger
BEFORE INSERT ON yourtable
FOR EACH ROW
SET new.combined = CONCAT(new.zipcode, ' - ', new.city, ', ', new.state);

CREATE TRIGGER update_trigger
BEFORE UPDATE ON yourtable
FOR EACH ROW
SET new.combined = CONCAT(new.zipcode, ' - ', new.city, ', ', new.state);

Answer 2

你确定你要这么做吗？实质上,您正在复制三个原始列中的数据.从那时起,您需要确保组合字段中的数据与前三列中的数据匹配.这对您的应用程序来说是更多的开销,而更新系统的其他进程需要了解这种关系.

如果您需要数据,为什么不在需要时选择？用于选择该字段中的内容的SQL将是:

SELECT CONCAT(zipcode, ' - ', city, ', ', state) FROM Table;

这样,如果字段中的数据发生更改,则无需更新组合字段.

Answer 3

向表中添加新列并执行查询:

UPDATE tbl SET combined = CONCAT(zipcode, ' - ', city, ', ', state)