Mikhail Gorbachev's policies of glasnost and perestroika had profound and unintended effects on the Soviet Union. In fact, many historians suggest these reforms led directly to the fall of communism and the breakup of the Soviet Union.
In SQL Server, you create a surrogate key by assigning an identity property to a column that has a number data type. A natural key is a naturally occurring descriptor of the data and one of a table's attributes that has no duplicate values. When you use a natural key as a table's primary key, each of the table's rows is uniquely identified.
Using correlated sub-queries in SQL Server. Possessing the ability to use a correlated sub-query will allow you to solve problems that other database developers cannot. Tim Chapman discusses how to use this extremely useful programming construct. A sub-query is a SQL Server statement embedded inside of another SQL Server statement. The database engine treats a sub-query as a virtual table for the execution of the query. A sub-query can be used as a table in a join statement, as a single value in a select statement, in the where clause of a SQL Server query, in the having clause of a SQL Server query, or incorporated in data manipulation statements. Sub-query execution is dependent upon the nesting level of the query.