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Using a unique combination of elements from the original SQL INSERT in a subsequent SELECT statement. Using a GUID in the SQL INSERT statement and retrieving it in a SELECT statement. Using the OUTPUT clause in the SQL INSERT statement for MS-SQL Server 2005 and MS-SQL Server 2008. Using an INSERT statement with RETURNING clause for Oracle.
It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to enforce uniqueness on the column you must include the appropriate constraint too. In Microsoft SQL Server you have options for both the seed (starting value) and the increment. By default the seed and increment are both 1.
A check constraint is a type of integrity constraint in SQL which specifies a requirement that must be met by each row in a database table. The constraint must be a predicate . It can refer to a single column, or multiple columns of the table.
Some DBMSs that are specialized for warehousing, such as Sybase IQ, use columnar storage by default, but the designer still sees only a single multi-column table. Other DBMSs, such as Microsoft SQL Server 2012 and later, let you specify a "columnstore index" for a particular table.
The referenced column(s) in the referenced table must be under a unique constraint, such as a primary key. Also, self-references are possible (not fully implemented in MS SQL Server though [ 5 ] ). On inserting a new row into the referencing table, the relational database management system (RDBMS) checks if the entered key value exists in the ...
For instance, a constraint can restrict a given integer attribute to values between 1 and 10. Constraints provide one method of implementing business rules in the database and support subsequent data use within the application layer. SQL implements constraint functionality in the form of check constraints.
The syntax to add such a constraint to an existing table is defined in SQL:2003 as shown below. Omitting the column list in the REFERENCES clause implies that the foreign key shall reference the primary key of the referenced table. Likewise, foreign keys can be defined as part of the CREATE TABLE SQL statement.
The formal definition of a database schema is a set of formulas (sentences) called integrity constraints imposed on a database. [citation needed] These integrity constraints ensure compatibility between parts of the schema. All constraints are expressible in the same language.