Create a new Column in database from data in existing column.

Question

I have a table

TableName: MACAddresses
Columns:
- Computer
- MACAddress

I would like to create a sql script that creates a new column and correctly formats the mac address with the colon (ie with Substring) - To create a new column called CorrectMAC

How would I do this with Oracle?

Answer 1

Here is some test data:

SQL> select * from MACAddresses
  2  /

  COMPUTER MACADDRESS
---------- ------------
       100 123456789abc
       200 acef35dd6ecc

SQL>

Adding the new column is quite straightforward:

SQL> alter table MACAddresses
  2      add corrected_MACAddress varchar2(17)
  3  /

Table altered.

SQL>

Note that you cannot make it NOT NULL at this point, because you already have some records in the table. So if you want to apply such a constraint, you need to populate it first.

This is the simplest way of updating the new column.

SQL> update MACAddresses
  2      set corrected_MACAddress = substr(macaddress, 1,2)||':'||
  3                                 substr(macaddress, 3,2)||':'||
  4                                 substr(macaddress, 5,2)||':'||
  5                                 substr(macaddress, 7,2)||':'||
  6                                 substr(macaddress, 9,2)||':'||
  7                                 substr(macaddress, 11,2)
  8  /

2 rows updated.

SQL> select * from MACAddresses
  2  /

  COMPUTER MACADDRESS   CORRECTED_MACADDR
---------- ------------ -----------------
       100 123456789abc 12:34:56:78:9a:bc
       200 acef35dd6ecc ac:ef:35:dd:6e:cc

SQL>

Now, if you had a more complicated pattern, or if you wanted to perform this operation on a regukar basis I suggest you expend the effort to turn it into a function, and perhaps remove that repetition at the same time.

Finally, if you wanted to enforce a mandatory constraint you can:

SQL> alter table MACAddresses
  2       modify corrected_MACAddress not null
  3  /

Table altered.

SQL>