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An index may be declared as UNIQUE, which creates an implicit constraint on the underlying table. Database systems usually implicitly create an index on a set of columns declared PRIMARY KEY, and some are capable of using an already-existing index to police this constraint.
In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...
A key that may become the primary key. Primary The key that is selected as the primary key. Only one key within an entity is selected to be the primary key. This is the key that is allowed to migrate to other entities to define the relationships that exist among the entities.
An important distinction between a surrogate and a primary key depends on whether the database is a current database or a temporal database. Since a current database stores only currently valid data, there is a one-to-one correspondence between a surrogate in the modeled world and the primary key of the database.
The differences between the two tend to be small; in fact, index funds and ETFs are often (but not always) the same thing. Thus, which one you choose is less important than the choice to start ...
A candidate key, or simply a key, of a relational database is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column could produce duplicate combinations of values. A candidate key is a minimal superkey, [1] i.e., a superkey that doesn't contain a smaller one. Therefore ...
As you can see, the key difference between index funds that track the same index is basically just the cost. That’s why experts tell investors to focus on the cost of funds when looking at funds ...
The index key that points to the second sibling must take the smallest value of that node to be the index key. - If re-distribute fails, merge L and sibling. After merging, the parent node is updated by deleting the index key that point to the deleted entry.