426 Part I EXAM PREPARATION more instances of
426 Part I EXAM PREPARATION more instances of SQL Server, hence the name distributed. Distributed partitioned views are used when processing needs to be spread throughout a group of servers, as shown in Figure 7.15. FIGURE 7.15 An illustration of a how a distributed partitioned view works. In simple words, with partitioned views, tables that store large amounts of data can be split up (using horizontal partitioning) into smaller member tables. This data in the member table holds the same number of columns as the original table; it is only the number of rows that is decreased. After the data is broken down into smaller member tables, a view defined with UNION ALL is used to bring all member tables together. This view looks like a single large resultset. When a SELECT query is run against the partitioned view, SQL Server uses CHECK constraints in determining which member table the data is from. The CHECK constraint is usually created on the Primary Key column. Partitioned View Considerations and Guidelines When creating partitioned views, you should give careful thought to a few considerations: Local partitioned views do not need to use CHECK constraints. Not using CHECK constraints also provides the same results as using a CHECK constraint, except that the Query Optimizer has to perform a lengthy search against all member tables meeting the query search condition. Using CHECK constraints reduces the cost of queries. When creating partitioned views, be sure that all columns of each member table are included in the partitioned view definition. Also, make sure that the same column is not referenced twice in the SELECT list. Make sure that all identical columns in all tables are of the same data type. When referencing member tables in a view, be sure to use the FROM clause to specifically declare a reference each table will use. Be sure that Primary Keys are defined on the same column for
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