Is it bad to use user name as primary key in database design?
I think he is right ( for the wrong reason) because primary key cannot change, but username can change. So you should use userid because it wouldn’t change.
unique-key
make text column as unique key
Basically you can not use Text column as UNIQUE key. Because practically such a big column will not be unique and there might be a chance of more duplicates. So go for hashing method and use that output as a UNIQUE constraint.
Oracle unique constraint and unique index
A constraint and an index are separate logical entities. A unique constraint, for example, is visible in USER_CONSTRAINTS (or ALL_CONSTRAINTS or DBA_CONSTRAINTS). An index is visible in USER_INDEXES (or ALL_INDEXES or DBA_INDEXES). A unique constraint is enforced by an index though it is possible (and sometimes necessary) to enforce a unique constraint using a non-unique … Read more
#1062 – Duplicate entry ” for key ‘unique_id’ When Trying to add UNIQUE KEY (MySQL)
The error says it all: Duplicate entry ” So run the following query: SELECT unique_id,COUNT(unique_id) FROM yourtblname GROUP BY unique_id HAVING COUNT(unique_id) >1 This query will also show you the problem SELECT * FROM yourtblname WHERE unique_id=” This will show you where there are values that have duplicates. You are trying to create a unique … Read more
MySQL: is primary key unique by default?
Primary key is always unique in every SQL. You dont have to explicitly define it as UNIQUE. On a side note: You can only have onePrimary key in a table and it never allows null values. Also you can have only one primary key constraint in the table(as the point of creating a primary key … Read more
Is the Sql Server Unique Key also an Index?
Unique Key: Unique Key enforces uniqueness of the column on which they are defined. Unique Key creates a non-clustered index on the column. Unique Key allows only one NULL Value. Alter table to add unique constraint to column: ALTER TABLE Authors ADD CONSTRAINT IX_Authors_Name UNIQUE(Name) GO Source More information from MSDN. FWIW — if your … Read more
MySQL – Make a pair of values unique
It’s called a composite key. If you want to change your actual PK to a composite one, use Alter table <your table> drop PRIMARY KEY; Alter table <your table> drop COLUMN <your autoincremented column>; Alter table <your table> add [constraint <constraint name>] PRIMARY KEY (<col1>, <col2>); You can also just add a unique constraint (your … Read more
Unique key with EF code first
Unfortunately you can’t define it as unique key in code first because EF doesn’t support unique keys at all (it is hopefully planned for next major release). What you can do is to create custom database intializer and add unique index manually by calling SQL command: public class MyInitializer : CreateDatabaseIfNotExists<MyContext> { protected override void … Read more
MySQL – Meaning of “PRIMARY KEY”, “UNIQUE KEY” and “KEY” when used together while creating a table
A key is just a normal index. A way over simplification is to think of it like a card catalog at a library. It points MySQL in the right direction. A unique key is also used for improved searching speed, but it has the constraint that there can be no duplicated items (there are no … Read more
How can I catch UniqueKey Violation exceptions with EF6 and SQL Server?
With EF6 and the DbContext API (for SQL Server), I’m currently using this piece of code: try { // Some DB access } catch (Exception ex) { HandleException(ex); } public virtual void HandleException(Exception exception) { if (exception is DbUpdateConcurrencyException concurrencyEx) { // A custom exception of yours for concurrency issues throw new ConcurrencyException(); } else … Read more