MySQL: Manually increment a varchar for one insert statement - mysql

Question

I am converting data from one database to another. The target db has a table called provider with primary key provider_no varchar(6).
I'm writing an insert to copy from source table to target table, and need an incremented key for provider_no. Is there a function to return even the iterations for one insert statement?
There are a lot more columns, but the basic problem i'm trying to solve is:
INSERT INTO `target`.`provider`
(`provider_no`,
`lastUpdateDate`)
SELECT
'', --incremented value
now()
from `source`.`provider`;
Auto Increment only works for int values, but i'm not at liberty here to change the data type.
Also, the source table doesn't have a usable primary key value that I can use for this copy.

Answer 1

To increment the varchar, first cast it to a number (either signed, or unsigned) like so:
INSERT INTO `target`.`provider`
(`provider_no`,
`lastUpdateDate`)
SELECT
cast(the_varchar_field as signed) + 1, --incremented value
now()
from `source`.`provider`;
Example:
mysql> select cast("001" as unsigned) + 1;
+-----------------------------+
| cast("001" as unsigned) + 1 |
+-----------------------------+
| 2 |
+-----------------------------+
Sorry, i thought you wanted to increment the varchar field from the source table.
To 'emulate' an auto increment field as you want to do, we can do it with variables like this:
insert into provider
select #cnt := #cnt +1, now()
from sourceprovider, (select #cnt := 0) q;
And here's a little demo: http://sqlfiddle.com/#!9/09fd4/1

Answer 2

Here's a solution I just implemented. There's a unique column called did on the source table, which I can use indirectly. There's probably a more elegant way to do it, but:
create table temp_key (
key_id int auto_increment primary key,
did varchar(4));
insert into temp_key (did) select did from source.provider;
INSERT INTO target.provider
(provider_no,
lastUpdateDate)
SELECT
k.key_id,
now()
FROM source.provider d
JOIN temp_key k on d.did = k.did;
drop table temp_key;