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Database indexing techniques
1.
2. • 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 :
3. • 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‘
4. • 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’
5. • 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.
6. • 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
7.
8. • 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.
9.
10. • 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.
11. • 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
12. • 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
13. • 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)
)
14. Cont
• CREATE TABLE lookup
(
id INT NOT NULL,
name CHAR(20),
PRIMARY KEY USING HASH (id)
)
