Search results
Results From The WOW.Com Content Network
A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. Indexes are used to quickly locate data without having to search every row in a database table every time said table is accessed.
In relational databases a virtual column is a table column whose value(s) is automatically computed using other columns values, or another deterministic expression. Virtual columns are defined of SQL:2003 as Generated Column, [1] and are only implemented by some DBMSs, like MariaDB, SQL Server, Oracle, PostgreSQL, SQLite and Firebird (database server) (COMPUTED BY syntax).
If a table includes an INTEGER PRIMARY KEY column, SQLite will typically optimize it by treating it as an alias for the rowid, causing the contents to be stored as a strictly typed 64-bit signed integer and changing its behavior to be somewhat like an auto-incrementing column. SQLite includes an option to create a table without a rowid column ...
A natural join is a type of equi-join where the join predicate arises implicitly by comparing all columns in both tables that have the same column-names in the joined tables. The resulting joined table contains only one column for each pair of equally named columns. In the case that no columns with the same names are found, the result is a ...
A right join is employed over the Target (the INTO table) and the Source (the USING table / view / sub-query)--where Target is the left table and Source is the right one. The four possible combinations yield these rules: If the ON field(s) in the Source matches the ON field(s) in the Target, then UPDATE
One method of copying an object is the shallow copy.In that case a new object B is created, and the fields values of A are copied over to B. [3] [4] [5] This is also known as a field-by-field copy, [6] [7] [8] field-for-field copy, or field copy. [9]
In a database, a table is a collection of related data organized in table format; consisting of columns and rows.. In relational databases, and flat file databases, a table is a set of data elements (values) using a model of vertical columns (identifiable by name) and horizontal rows, the cell being the unit where a row and column intersect. [1]
An identity column differs from a primary key in that its values are managed by the server and usually cannot be modified. In many cases an identity column is used as a primary key; however, this is not always the case. It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to ...