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I have a Users table, which has a Unique constraint on the username (for obvious reasons).
I am using an EF 4.0 DAL to populate the database, and in the process of coding the CreateUser() method.
Is it...
If you could also give reasons as to why, that would be great!
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INSERT DISTINCT Records INTO New Tables In order to copy data from an existing table to a new one, you can use the "INSERT INTO SELECT DISTINCT" pattern. After "INSERT INTO", you specify the target table's name - organizations in the below case.
The syntax for creating a unique constraint using an ALTER TABLE statement in SQL Server is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ... column_n); table_name.
A table can have more than one unique key unlike primary key. Unique key constraints can accept only one NULL value for column. Unique constraints are also referenced by the foreign key of another table.
Yes a table can have n number of unique and foreign keys. Unique key constraints are used to ensure that data is not duplicated in two rows in the database. One row in the database is allowed to have null for the value of the unique key constraint.
I would check if the record exists first. Unique key constraints are useful to guard against possible ways your application is allowing "bad" data through in the first place, but not the main stop for that. It's generally a bad idea to use exceptions as a control flow mechanism (validation in this case) when it's possible to avoid.
EDIT: To avoid confusion, I'm not saying don't have the unique index at all. It should be there, but it shouldn't be the primary means of checking for uniqueness.
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