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    <p>Here is some test data:</p> <pre><code>SQL&gt; select * from MACAddresses 2 / COMPUTER MACADDRESS ---------- ------------ 100 123456789abc 200 acef35dd6ecc SQL&gt; </code></pre> <p>Adding the new column is quite straightforward:</p> <pre><code>SQL&gt; alter table MACAddresses 2 add corrected_MACAddress varchar2(17) 3 / Table altered. SQL&gt; </code></pre> <p>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. </p> <p>This is the simplest way of updating the new column. </p> <pre><code>SQL&gt; 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&gt; 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&gt; </code></pre> <p>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.</p> <p>Finally, if you wanted to enforce a mandatory constraint you can:</p> <pre><code>SQL&gt; alter table MACAddresses 2 modify corrected_MACAddress not null 3 / Table altered. SQL&gt; </code></pre>
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    1. COYou could use that 'from dual connect by level' trick to do an arbitrary number of splits. Or an incomprehensible regexp on Oracle 10!
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    2. COOn 11g, this would be a good candidate for a virtual column, which would ensure that it is always consistent with the primary field.
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