unique-key

I want to add complex unique key to existing table. Key contains from 4 fields ( user_id , game_id , date , time ). But table have non unique rows. I understand that I can remove all duplicate dates and after that add complex key. Maybe exist another solution without searching all duplicate data. (like add unique ignore etc). UPD I searched, how can remove duplicate mysql rows - i think it's good solution. Remove duplicates using only a MySQL query? Igor Lozovsky You can do as yAnTar advised ALTER TABLE TABLE_NAME ADD Id INT IDENTITY(1,1) PRIMARY KEY OR You can add a constraint ALTER TABLE

Can anyone explain about the purpose of PRIMARY KEY , UNIQUE KEY and KEY , if it is put together in a single CREATE TABLE statement in MySQL? CREATE TABLE IF NOT EXISTS `tmp` ( `id` int(11) NOT NULL AUTO_INCREMENT, `uid` varchar(255) NOT NULL, `name` varchar(255) NOT NULL, `tag` int(1) NOT NULL DEFAULT '0', `description` varchar(255), PRIMARY KEY (`id`), UNIQUE KEY `uid` (`uid`), KEY `name` (`name`), KEY `tag` (`tag`) ) ENGINE=InnoDB AUTO_INCREMENT=1 ; How do I convert this query to MSSQL? A key is just a normal index. A way over simplification is to think of it like a card catalog at a

I know what the term "SuperKey" in SQL stands for, but I cannot understand a specific thing and I would like some help. In a table with no data , is there a superkey? In any table, will there always exists one? TL;DR "Superkey" is a RM (Relational Model of Data) term. There's no standard use in SQL. The superkeys of an SQL table might reasonably informally be said to be the column sets that you could declare primary key or unique not null , plus maybe {} when a table holds at most one row (although you can't declare it). "Reasonably informally" because SQL tables are not RM relations. But if a

I have a table with 4 columns: ID, type, owner, description. ID is AUTO_INCREMENT PRIMARY KEY and now I want to: ALTER IGNORE TABLE `my_table` ADD UNIQUE (`type`, `owner`); Of course I have few records with type = 'Apple' and owner = 'Apple CO'. So my question is which record will be the special one to stay after that ALTER TABLE, the one with smallest ID or maybe the one with biggest as the latest inserted? Galz The first record will be kept, the rest deleted §§ : IGNORE is a MySQL extension to standard SQL. It controls how ALTER TABLE works if there are duplicates on unique keys in the new

An existing DB schema has unique, non-primary, keys, and some foreign keys that rely on them. Is it possible to define unique keys, which are not primary keys, in Entity Framework v4? How? Evandro Pomatti The Entity Framework 6.1 now supports uniques with both Data Annotations and Fluent API. Data Annotations ( Reference ) public class MyEntityClass { [Index(IsUnique = true)] [MaxLength(255)] // for code-first implementations public string MyUniqueProperty{ get; set; } } Fluent API ( Reference ) public class MyContext : DbContext { protected override void OnModelCreating(DbModelBuilder