MySQL - 如何在 ALTER TABLE 中使用 CONCAT？

Question

How do I concatenate in ALTER TABLE ?

I tried this, but it didn't work:

$sql1="ALTER TABLE t1 ADD iod = CONCAT('10.1234','/',id)"; 

id is a different column in the same table.

Answer 1

You're misusing ALTER TABLE . It is intended to modify the data definition (structure) of a table, not its values.

If you want to modify the values in a table, you should use one of the following types of queries:

• INSERT
• UPDATE
• DELETE

Answer 2

Use update after you add a column to fill it out:

ALTER TABLE t1 ADD iod varchar(150)
UPDATE t1 SET iod = CONCAT('10.1234','/',id)

Any new rows that you add would have to include the proper value of iod . Computed columns would solve this, but I don't think they're available on MySQL.