Technically yes, but if a string makes sense to be the primary key then you should probably use it. This all depends on the size of the table you’re making it for and the length of the string that is going to be the primary key (longer strings == harder to compare). I wouldn’t necessarily … Read more
ALTER TABLE provider ADD PRIMARY KEY(person,place,thing); If a primary key already exists then you want to do this ALTER TABLE provider DROP PRIMARY KEY, ADD PRIMARY KEY(person, place, thing);
I would use a composite (multi-column) key. CREATE TABLE INFO ( t1ID INT, t2ID INT, PRIMARY KEY (t1ID, t2ID) ) This way you can have t1ID and t2ID as foreign keys pointing to their respective tables as well.
drop constraint and recreate it alter table Persion drop CONSTRAINT <constraint_name> alter table Persion add primary key (persionId,Pname,PMID) edit: you can find the constraint name by using the query below: select OBJECT_NAME(OBJECT_ID) AS NameofConstraint FROM sys.objects where OBJECT_NAME(parent_object_id)=’Persion’ and type_desc LIKE ‘%CONSTRAINT’
It doesn’t matter. pk is more independent from the actual primary key field i.e. you don’t need to care whether the primary key field is called id or object_id or whatever. It also provides more consistency if you have models with different primary key fields.
(Updated – Thanks to the people who commented) Modern Versions of PostgreSQL Suppose you have a table named test1, to which you want to add an auto-incrementing, primary-key id (surrogate) column. The following command should be sufficient in recent versions of PostgreSQL: ALTER TABLE test1 ADD COLUMN id SERIAL PRIMARY KEY; Older Versions of PostgreSQL … Read more
KEY and INDEX are synonyms in MySQL. They mean the same thing. In databases you would use indexes to improve the speed of data retrieval. An index is typically created on columns used in JOIN, WHERE, and ORDER BY clauses. Imagine you have a table called users and you want to search for all the … Read more
Primary Key: There can only be one primary key constraint in a table In some DBMS it cannot be NULL – e.g. MySQL adds NOT NULL Primary Key is a unique key identifier of the record Unique Key: Can be more than one unique key in one table Unique key can have NULL values It … Read more
“Hash and Range Primary Key” means that a single row in DynamoDB has a unique primary key made up of both the hash and the range key. For example with a hash key of X and range key of Y, your primary key is effectively XY. You can also have multiple range keys for the … Read more
No – you have to do it the other way around: add it right from the get go as INT IDENTITY – it will be filled with identity values when you do this: ALTER TABLE dbo.YourTable ADD ID INT IDENTITY and then you can make it the primary key: ALTER TABLE dbo.YourTable ADD CONSTRAINT PK_YourTable … Read more