问题
How can I append a string to the end of an existing table value? Let's say I have the table below:
And let's say that Maria Anders not only lived in Berlin but also Tokyo. How would I append the string
" Tokyo" onto the City column where ContactName = Maria Anders?
P.S. I want to be able to append on to a null value as well. Thus ending up with just the one city.
回答1:
Use a combination of CONCAT and IFNULL (to handle the NULL case):
UPDATE `table`
SET `City` = IFNULL(CONCAT(`City`, " Tokyo"), "Tokyo")
WHERE `ContactName` = "Maria Anders";
However, appending seems wrong. If you want multiple City values (a many-to-many relationship), you should have a separate table for cities and a separate table for person-city relationships. Read about database normalisation.
回答2:
You shouldn't have nested lists inside of a table. I would first create a table that associates each person with a unique ID. This is important in case you have someone else down the road with the same name.
ID | ContactName
----+---------------
23 | Maria Anders
Then have each location associated with an ID - For example:
ID | Address | City
----+-----------+------
Then when you need to add a new location for the same person, you can just add another value. For example:
ID | Address | City
----+-----------+------
23 | Foo ST. | Baria
23 | Bar Ave. | Fooia
Fetching the data and creating a list in your application/website will then be easy, as well as more flexible. Check out information on building one-to-many relationship tables via Google or the other places people suggested.
来源：https://stackoverflow.com/questions/5524872/mysql-append-string