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Database indexing techniques

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Database indexing techniques ... search data from database using different data structures like trees , hashing and also learn indexing quries

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Database indexing techniques

  1. 1. • A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. • Example :
  2. 2. • Now, let’s say that we want to run a query to find all the details of any employees who are named ‘Jesus’? So, we decide to run a simple query like this: • Example : • SELECT * FROM Employee WHERE Employee_Name = 'Jesus‘
  3. 3. • Well, the database software would literally have to look at every single row in the Customers table to see if the customerName for that row is ‘Jesus’
  4. 4. • The whole point of having an index is to speed up search queries by essentially cutting down the number of records/rows in a table that need to be examined.
  5. 5. • B- trees are the most commonly used data structures for indexes. • Time efficient • Deletions, and insertions can all be done in logarithmic time • No need to sort data just use algorithm to get sorted data like inorder,postorder etc • No need to search whole table
  6. 6. • Queries that compare for equality to a string can retrieve values very fast if they use a hash index. • Example : SELECT * FROM Employee WHERE Employee_Name = ‘Jesus’ • Hash tables are not sorted data structures. • Suppose you want to find out all of the employees who are less than 40 years old. How could you do that with a hash table index? Well, it’s not possible because a hash table is only good for looking up key value pairs.
  7. 7. • A database index does not store the values in the other columns of the same table. • Example: Age and Employee_Address column values are not also stored in the index. • An index stores a pointer to the table row.
  8. 8. • Syntax: CREATE INDEX name_indexON Employee (Employee_Name) • How to create a multi-column index in SQL • Syntax: CREATE INDEX name_indexON Employee (Employee_Name, Employee_Age) • ALTER TABLE tbl_name ADD PRIMARY KEY (column_list): This statement adds a PRIMARY KEY, which means that indexed values must be unique and cannot be NULL
  9. 9. • It takes up space – and the larger your table, the larger your index. • Whenever you add, delete, or update rows in the corresponding table, the same operations will have to be done to your index. • Drop unused indexes Syntax: Alter table admin drop index searchAge
  10. 10. • SHOW INDEX FROM table_name • ALTER TABLE testalter_tbl ADD PRIMARY KEY (i); • ALTER TABLE testalter_tbl DROP PRIMARY KEY; • CREATE TABLE lookup ( id INT NOT NULL, name CHAR(20), PRIMARY KEY USING BTREE (id) )
  11. 11. Cont • CREATE TABLE lookup ( id INT NOT NULL, name CHAR(20), PRIMARY KEY USING HASH (id) )

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