1. SQL Transactions
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2. Objective To develop an understanding of the role of SQL transactions
To study mechanisms available for encapsulating SQL transactions
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3. SQL Routines
A routine is a number of SQL statements defined as a compound statement which is stored by the DBMS and executed as a single action.
Standardised through SQL/PSM 1996 (Persistent Stored Modules).
Two kinds-functions and procedures.
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4. Functions e.g. Create Function greater(a integer, b integer)
Create Function greater(a integer, b integer)
Returns integer
Begin
If a>b then
Return a;
Else
Return b;
End if
End
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5. Example Create function city_pop(my_city varchar(24))
Returns decimal(6,1)
Begin
Declare my_pop decimal (6,1);
Select population
Into my_pop
From city
Where name=my_city;
Return my_pop;
End
Used like functions such as sum, count etc..
e.g. select city_pop(‘london’);
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6. Procedures Create procedure proc_pop (in my_city varchar(24),
Create procedure proc_pop
(in my_city varchar(24),
out my_pop decimal(6,1))
Begin
Select population
Into my_pop
From city
Where name=my_city;
End
Call proc_pop('Paris', paris_pop)
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7. Routines can be given access privileges
Grant execute on city_pop to admin;
Execute privilege gives a user access to a database table without any other privileges.
So, access for very specific purposes can defined.
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8. SQL*Server-Stored Procedures
These are persistent re-useable programs written in an extended form of SQL (extended to include flow-of-control statements).
Create procedure name parameter_list
As sql_statements;
Simple example (no parameters)-
Create procedure all_employees
As select * from employee;
Procedure is invoked by-
Execute all_employees;
(may work by simply executing the procedure name)
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9. Example using parameters- Create procedure work_proc
int) as
Insert into worker
Values
@ indicates a parameter (which can be used in the same manner as variables in other programming languages).
Cannot use text or image data types for parameters/variables.
This can be invoked thus-
Work_proc ('Bob Smith','Sales',3333);
This inserts a single row of data into the worker table.
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10. Global variables are referenced using @@.
Only local variables can be declared.
Global variables are defined and made available by SQL*Server. 
Lists of global variables in Transact*SQL Help under ‘globals’.
Used mainly for system and status information.
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11. sp_helptext work_proc Stored procedures are removed using
Stored procedures sp_help and sp_helptext can be used to gain information on your stored procedures.
e.g.
sp_helptext work_proc
Stored procedures are removed using
Drop procedure work_proc
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12. Using Flow-of-Control
The various components are illustrated in the following simple examples-
int {Declaring variables}
int
Select values}
Begin
Print 'x still less than 5'
Select ……….{incrementing variable values}
Select
Print 'y is 2 so break out of loop'
Break …….{jumping out of loop....}
End
Print 'out of while loop'
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13. Next example- Begin tran …{begin transaction}
While (select avg(price) from titles)<30
Begin
Select title_id, price From title Where price>20
Update title set price=price*2
End
End tran
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14. Returning Values Procedures can call other procedures.
The only value that can be returned is an integer.
This may be a status value from SQL*Sever indicating success or otherwise of the procedure.
Or it might be a value provided by the called procedure. Values 0, -1 to -14 are system status values.
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15. Values received using- Execute @return_status=procedure_name
Select
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16. Summary SQL operations can be encapsulated into transactions
These can be in the form of persistent functions or procedures
SQL is extended to include parameter passing and flow-of-control statements
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