Generating sequence number

OPTION 1:
Create an ID field in your database. Keep it as Integer type and auto-increment by 1 each time. (this can be done in DB very easily while setting up a table!)

Now since, its just the fixed letter 'ELG', append that whenever you are using them either in query while fetching data or in UI while using it whereever suits you.

OPTION 2:
Create an ID, TempID field in your database. Keep ID field as nvarchar(10) type and TempID field as Ineger type and auto-incrementable by 1.

Now, at the time of inserting record in table:

1. You can put up on ID field that insert "ELG"+TempID.
2. OR You can use TRIGGER to insert value

For having sequential numbers, you can have any logic you like. You can even pass it from frontend.