PROCEDURAL DATABASE PROGRAMMING ( PL/SQL AND T-SQL)

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1 Technology & Information Management Instructor: Michael Kremer, Ph.D. Class 5 Database Programming PROCEDURAL DATABASE PROGRAMMING ( PL/SQL AND T-SQL)

2 AGENDA 7. Stored Procedures 7.1 Introduction to Stored Procedures 7.2 Basic Stored Procedures 7.3 Parameters 7.4 Overloading Procedures

3 Procedural Database Programming (PL/SQL and T-SQL) 7. STORED PROCEDURES

4 7.1 INTRODUCTION TO STORED PROCEDURES 123 Stored procedures are the main modules holding the majority of database code A human mind is not a massively parallel computer We need to break down huge, intimidating projects into smaller, more manageable components, then further decompose those components into individual programs Therefore, you want to write modular code The benefits are: More reusable: Small programs are more likely to be reused More manageable: Focus on smaller tasks is easier, therefore, programs should be small More readable: Modules have names, and names describe behavior Code behind a well described programmatic interface becomes selfdocumenting More reliable: Code in smaller program units will have fewer errors, and if errors occur, they are easier to find

5 7.1 INTRODUCTION TO STORED PROCEDURES 124 Module refers to either a function, stored procedure or trigger Stored procedures(sp) are executable server-side routines Unlike functions, you can issue DML statements in a SP Furthermore, stored procedures can be used as a security layer (You control access to objects by granting permissions) Perform input validation, and allow activities only if they make sense as a whole unit SP give you the benefit of encapsulation You can simply change a SP by using the ALTER PROCEDURE statement to modify As long as the procedure s interface (name, parameters) does not change, users and applications are not affected SP also provide many important performance benefits. They are cached on the database server

6 7.2 BASIC STORED PROCEDURES 125 Stored Procedures accept parameters from the caller Parameters are contained in comma-separated list in parentheses following the procedure name SP can also return more than one OUT parameter SQL Server only, RETURN statement can return integer datatype, if not used, it returns error number (0 means no error) ;number can be used to group procedures together having the same name

7 7.2 BASIC STORED PROCEDURES 126 Values of each declared parameter must be supplied when procedure is called Parameters can be assigned a value, this serves as a default value Parameters are local to the procedure, same name can be reused in another stored procedure Datatype can be any valid T-SQL datatype Also user-defined datatypes such as table types, must be set to ReadOnly Cursor datatype can only be used as OUTPUT parameter Varying keyword must be used with Cursor datatype: It means that the datatype is dynamically constructed at runtime and its content changes

8 7.2 BASIC STORED PROCEDURES 127 If a default value is defined, the procedure can be called without specifying a value for that parameter Default value must be a constant/literal or null, cannot be an expression OUTPUT designates parameter as a return value: Text, ntext, and image datatypes cannot be used as output READONLY specifies that that the parameter cannot be updated or modified within the body of the procedure Procedure options: RECOMPILE: Execution plan is not cached and procedure is compiled at run time ENCRYPTION: Convert original text (DDL statement) into an obfuscated format

9 7.2 BASIC STORED PROCEDURES 128 Oracle syntax is similar Procedure name can be at most 30 characters long Parameters can be IN, OUT and IN OUT. This is different compared to SQL Server AUTHID defines whether procedure will be executed with privileges of the definer(owner) or the current user Declarations is used to declare local variables to be used in stored procedure Syntax for calling stored procedures is similar in both db platforms when no out/output parameters are involved Use keyword exec followed by procedure name and arguments when called from query/worksheet interface Calling from another SP: SQL Server(exec SP_name), Oracle(SP_name)

10 7.2 BASIC STORED PROCEDURES 129

11 7.2 BASIC STORED PROCEDURES 130

12 7.2 BASIC STORED PROCEDURES 131

13 7.2 BASIC STORED PROCEDURES 132

14 7.3 PARAMETERS 133 Parameters are used to pass information back and forth between calling environment and procedure/function Procedure name and parameters form the procedure s interface or contract It is crucial to carefully design and implement the list of parameters Once a program is in use, changes to the procedure will not break any calls from other units unless the parameters are changed! Important design decisions for parameters: Number of parameters: Balance between too few (limits reusability) and too many (maintenance) Types of parameters: IN, OUT, or IN OUT (Oracle), also datatypes. VARCHAR is the most flexible, can always convert within procedure Names of parameters: Important for understanding program unit Default values: When and when not to use default values Oracle: unconstrained datatypes, VARCHAR2 and not VARCHAR2(100) Oracle: IN, OUT, IN OUT SQL Server: IN, IN OUT only

15 7.3 PARAMETERS 134 Different types of parameters Note: Only IN parameters can have default values

7.3 PARAMETERS 135 When using parameters, there are two sides: IN Mode Calling environment: Arguments Receiving environment: Parameters Names of arguments and

16 7.3 PARAMETERS 135 When using parameters, there are two sides: IN Mode Calling environment: Arguments Receiving environment: Parameters Names of arguments and parameters do not have to match Default mode, IN keyword optional in Oracle, does not exist in SQL Server (is always assumed) IN parameter acts like a constant, cannot be changed

7.3 PARAMETERS 136 In SQL Server, only literals or local variables are allowed as IN parameters OUT Mode (Oracle only) To return values to calling environment, a function can only return one value, a

17 7.3 PARAMETERS 136 In SQL Server, only literals or local variables are allowed as IN parameters OUT Mode (Oracle only) To return values to calling environment, a function can only return one value, a stored procedure many However, stored procedure cannot be used in declarative SQL call OUT parameter acts like a variable that has not been initialized OUT parameter value is assigned only when program terminates successfully

18 7.3 PARAMETERS 137 Rules for OUT parameters: IN OUT Mode Oracle: IN OUT, SQL Server: OUTPUT (IN is assumed) Rules for IN OUT parameters Calling Syntax:

19 7.3 PARAMETERS 138

20 7.3 PARAMETERS 139

21 7.3 PARAMETERS 140

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23 7.3 PARAMETERS 142 Parameter Association Positional notation, matching arguments with parameters by position Works well when there are few parameters and no defaults In case of many parameters and some of them are defaults, use named notation In the procedure call, you match argument with parameter Named notation: Difference is only association operator

24 7.3 PARAMETERS 143 Named Notation is self documenting: Clearly describes which argument is mapped to which parameter Parameter names should be self-explanatory Named Notation is more flexible: List arguments/parameters in any order Only use parameters that you want/need

25 7.3 PARAMETERS 144

26 7.3 PARAMETERS 145

27 7.3 PARAMETERS 146

28 7.3 PARAMETERS 147

7.4 OVERLOADING PROCEDURES 148 When more than one program in the same scope share the same name, the programs are said to be overloaded Oracle supports overloading, SQL Server does not (simulate by

29 7.4 OVERLOADING PROCEDURES 148 When more than one program in the same scope share the same name, the programs are said to be overloaded Oracle supports overloading, SQL Server does not (simulate by using default values) Benefits of overloading: Supporting many data combinations: Same action to different kinds of data, overloading provides different ways of requesting the same activity (most common motivation for overloading) Fitting the program to the user: Construct different versions of the same program correspond to different patterns of use Overloading by type, not by value: Use different datatypes for the same kind of activity of a program.

30 7.4 OVERLOADING PROCEDURES 149 Next example we need to calculate the number of years an employee worked for a startup company. Company was founded on May 1, 1999 Functionality: The first two functions are designed for employees who worked for the company since the inception, therefore, they get the additional benefit of the rounding up to the next higher number

31 7.4 OVERLOADING PROCEDURES 150

32 7.4 OVERLOADING PROCEDURES 151

7.4 OVERLOADING PROCEDURES 152 SQL Server function seems simpler But just think that these different functionalities were developed over time In the beginning, there was only one function since all

33 7.4 OVERLOADING PROCEDURES 152 SQL Server function seems simpler But just think that these different functionalities were developed over time In the beginning, there was only one function since all employees were part of the founding team Over time, more employees were hired having a different start date. That calls for a new procedure Rather than changing the existing one, add an overloaded function In SQL Server, you have to change the existing function More regression testing is needed to ensure no existing functionality is broken!

PROCEDURAL DATABASE PROGRAMMING ( PL/SQL AND T-SQL)

Technology & Information Management Instructor: Michael Kremer, Ph.D. Class 4 Database Programming PROCEDURAL DATABASE PROGRAMMING ( PL/SQL AND T-SQL) AGENDA 6. Stored Functions Procedural Database Programming