rups:

As LanX indicated, that's the kind of work you can have your database do. In fact, you can also prevent duplicates from being inserted into the table by putting a unique index on the ConsumeMobNo column. However, that table looks like it will be a problem in the future: You're forcing a 1:1 relationship between customers and mobile phone numbers. I'd personally have a table that has the phone number as the primary key and have a foreign key relationship to the consumeruser table.

...roboticus

When your only tool is a hammer, all problems look like your thumb.