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Database index

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How to create indexes. Where to start and best practices

How to create indexes. Where to start and best practices

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  • 1. DATABASE INDEX Sql Server, Mysql, Oracle
  • 2. Database Without Index  Lets assume Sql Server, MySql and Oracle doesn’t support Index.  How to handle this siltation?  Why Indexes has introduced in the database?
  • 3. Benefit of In Built Index  Data synchronization  When data is inserted in the table, same data is also inserted into the index.  When data is deleted from the table same, data is also deleted from the index.  When data is updated in the table, same data is also updated in the index.
  • 4. How To Create Indexes? CREATE TABLE tblEmployee( ntEmployeeID BIGINT PRIMARY KEY, vcEmpName VARCHAR(200), dtDoj DATETIME, btGender BIT, vcSkill VARCHAR(2000), moSalary MONEY, ntHirarchyID BIGINT )
  • 5. Common Misconception  Table design doesn’t decide index.  It may help some extent .  Primary key should be primary index (Clustered index) of a table.  All tables should have a clustered index on a primary key column
  • 6. Where To Start?  OLAP (Online Analytical Processing)  OLTP (Online Transaction Processing)  What data is needed from a table?  What queries are executing on a table?
  • 7. How To Know What Queries Are Executing ?  Find out all the in-lines queries.  Find out all the queries from stored procedures and database functions.  Use DMVS or metadata tables to get queries.
  • 8. Steps To Create Indexes  Identify the application nature(OLAP OLTP)  OLAP: Create index if necessary.  OLTP: Create index if very necessary.  OLAP + OLTP  Sort the all queries on the base of frequency of execution and query execution time.
  • 9. Rule 1  Create indexes on a table if the queries which fetch data from a table have at least following clauses: Clause Logical Processing Order ON 1 WHERE 2 GROUP BY 3 HAVING 4 ORDER BY 5 DISTINCT 6 UNION NA EXCEPT NA INTERSECT NA
  • 10. Rule 2  Create index on the fields in which data are filtered only using following operators in WHERE clause, ON clause and HAVING clause: Operator Type = Equality < Range > Range <= Range >= Range IN Range BETWEEN Range LIKE Range
  • 11. Rule 3  Don't create indexes on the columns which are expression in the query.  We will discuss later how to create indexes of such predicates.
  • 12. Order of column name in an index  Index 1: CREATE INDEX NCI_a_b ON tblEmployee(a,b)  Index 2: CREATE INDEX NCI_b_a ON tblEmployee(b,a)  Here index NCI_a_b and NCI_b_a are two totally different indexes.
  • 13. Rule 4  Try to avoid creating single column indexes if multi column index is possible.  If we are creating multi column index, keep columns order according to logical order of processing of different clauses.
  • 14. Rule 5  Keep the all columns with equality operator first.  One columns with range operators is allowed .  If columns with range operator has not included then only columns in GROUP BY Clause or ORDER BY clause should be included.
  • 15. Rule 6  If there are two columns with equality operator then column which has most number of distinct values should be included first.

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