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A table can have one of the following index configurations: No indexes  A clustered index A clustered index and many nonclustered indexes A nonclustered index Many nonclustered indexes

What are the different index configurations a table can have? A table can have one of the following index configurations: No indexes A clustered index A clustered index and many nonclustered indexes A nonclustered index Many nonclustered indexes

What is the difference between clustered and a non-clustered index? A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

What is Index? An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes, they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance. Clustered indexe s define the physical sorting of a database table’s rows in the storage media. For this reason, each database table may have only one clustered index. Non-clustered indexes are created outside of the database table and contain a sorted list of references to the table itself.

As all of us know it is very typical to choose column for non cluster index. We should consider creating non-cluster index on any column that are frequently referenced in the where clauses of Sql statements.we may wish to also consider creating non-clustered indexes that cover all of the columns used by certain frequently issued queries. These queries are referred to as covered queries and experience excellent performance gains. Index Tuning is the process of finding appropriate column for non-clustered indexes. SQL Server provides a wonderful facility known as the Index Tuning Wizard which greatly enhances the index selection process.

Composite index is an index on two or more columns. Both clustered and nonclustered indexes can be composite indexes. Composite indexes are especially useful in two different circumstances. First, you can use a composite index to cover a query. Secondly we can use a composite index to help match the search criteria of specific queries.

Indexes help us retrieve data from tables quicker. Let's use an example to illustrate this point: Say we are interested in reading about how to grow peppers in a gardening book. Instead of reading the book from the beginning until we find a section on peppers, it is much quicker for us to go to the index section at the end of the book, locate which pages contain information on peppers, and then go to these pages directly. Going to the index first saves us time and is by far a more efficient method for locating the information we need. The same principle applies for retrieving data from a database table. Without an index, the database system reads through the entire table (this process is called a 'table scan') to locate the desired information. With the proper index in place, the database system can then first go through the index to find out where to retrieve the data, and then go to these locations directly to get the needed data. This is much faster. ...

SQL Index Index in sql is created on existing tables to retrieve the rows quickly. When there are thousands of records in a table, retrieving information will take a long time. Therefore indexes are created on columns which are accessed frequently, so that the information can be retrieved quickly. Indexes can be created on a single column or a group of columns. When a index is created, it first sorts the data and then it assigns a ROWID for each row. Syntax to create Index: CREATE INDEX index_name ON table_name (column_name1,column_name2...); Syntax to create SQL unique Index: CREATE UNIQUE INDEX index_name ON table_name (column_name1,column_name2...); index_name is the name of the INDEX. table_name is the name of the table to which the indexed column belongs. column_name1, column_name2.. is the list of columns which make up the INDEX. In Oracle there are two types of SQL index namely, implicit and explicit. Implicit Indexes: They are created when a column i...