1. Introduction To DBMS and
MySQL
UDF, Views, Indexing
Week 6 – Day2

2. User Defined functions [ UDF ]

3. User Defined functions UDF
• A function is a subprogram written to
perform certain computations
• It can be used with sql select queries
same like we use any other scalar or
aggregate functions that we discussed
earlier (eg: sum(), Avg() etc)

4. Example
• Write a function that returns Holiday or working day depending upon the
day of week. If it is Saturday or Sunday it should display holiday or else
working day
DELIMITER //
CREATE FUNCTION fun_getDAy(x datetime) RETURNS VARCHAR(15)
BEGIN
DECLARE dayname varchar(15) DEFAULT ‘HOLIDAY’;
IF(WEEKDAY(x)<5) THEN
SET dayname=‘WORKING DAY’;
END IF;
RETURN dayname;
END //
DELIMITER ;

5. Difference Between SP and UDF
• Functions are compiled and
executed at run time thus pretty
slower than stored procedure
• UDF can’t perform DML operations
like insert, update, delete etc but
the same can do from SP
• UDF cant call a Stored Procedure or
another UDF inside a UDF
• UDF must return a value
• Procedueres are compiled and
stored . So at run time no need of
compilation required which makes
pretty much faster
• SP can perform all DDL,DML and
DCL operations
• Stored procedure can call a UDF or
another stored procedure inside it
• Stored procedure may or may not
return any values

6. Views

7. Views
• A view is a customized representation of
data from one or more tables. The table
that the view is referencing are known as
base tables.
• A view can be considered as a stored
query or a virtual table
• View Doesn't take any storage space

8. Example
• Creating a view
– Create View view_teacher as select * from
tbl_teacher where teacher_name like „t%‟
• Using a View
–We can query against a view as we do
in a table
–Select * from view_teacher where
teacher_id=1

9. Advantages of View
• Data Security
– No need to give permission on the table. infact a view
can be created, having only selected number of
columns in its definition. So user will only be able to
see those columns
• Simplicity
• A very complicated query can be saved as a view
definition. When needed can be called by its view
name
• Removes Dependency
• Can be very helpful to remove the dependency from
the underlying tables. Suppose a view is created
joining several tables. After some time, there are some
changes on the table, so only definition of view can be

10. Indexing

11. Indexing
• A database index is a data structure that
improves the speed of operations in a table.
• Without an index, MySQL must begin with the
first row and then read through the entire table
to find the relevant rows. The larger the table,
the more this costs.
• INSERT and UPDATE statements take more
time on tables having indexes where as
SELECT statements become fast on those
tables. The reason is that while doing insert

12. Indexing
• Syntax
– CREATE INDEX index_name ON table_name
( column1, column2,...);
• Example
– CREATE INDEX AUTHOR_INDEX ON
tutorials_tbl (tutorial_author)

13. Points to be noted
• In Mysql whenever you create a table with
primary key, the same column will be
indexed
• So you don‟t have to explicitly create an
index for primary key column
• Simply below also a way of indexing a
table
– ALTER TABLE testalter_tbl ADD PRIMARY

14. Questions?
“A good question deserve a good
grade…”

15. End of day