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

Transcription

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

2 AGENDA 6. Stored Functions

3 Procedural Database Programming (PL/SQL and T-SQL) 6. STORED FUNCTIONS

4 6.1 INTRODUCTION TO FUNCTIONS 89 A function is a database object to hold procedural code. It can accept parameters and also returns a value back to the calling environment. It is different from a stored procedure in that a SP cannot inherently return a value. Therefore, functions can be used in regular SQL statements. Benefits of functions: Modular Programming: Reusable code stored once in the database Performance: Compiled, optimized and cached code. Network Traffic: Reducing number or rows returned in SQL by using functions in WHERE clauses. Function s code is not allowed to modify data (DML statements).

5 6.1 INTRODUCTION TO FUNCTIONS 90 Header: Function name and parameters define unique signature. Return datatype defines the kind of data being returned. Return datatype must be a db datatype and not a procedural datatype! Declaration: To declare local variables in function. Execution: The actual body of the function, executable part. Exception: Error handling To return error information, use VARCHAR or NUMBER as return datatype. Header Declaration Execution Exception Function Structure Function Name Parameters (Optional) Return Datatype Function Options Local Variables Procedural Code SQL Statements Return Statement(s) (at least one) Handle Exceptions Return Statement (optional)

6 6.2 WRITING BASIC FUNCTIONS 91 Based on the return datatype, SQL Server defines scalar and table valued functions. Inline function is comprised of one executable statement without BEGIN or END keyword. Multi-statement function contains many executable statements.

7 6.2 WRITING BASIC FUNCTIONS 91 Oracle Syntax Keyword RETURN (Oracle) vs. RETURNS (SQL Server)

8 6.2 WRITING BASIC FUNCTIONS 92

9 6.2 WRITING BASIC FUNCTIONS 93

10 6.2 WRITING BASIC FUNCTIONS 94 Return/Returns Datatype In general, functions return simple or scalar data. Sometimes they return objects, table-type data, and collections. When returning scalar data, include function as column expression in SQL statement. Table-type data, Oracle and SQL Server are different.

11 6.2 WRITING BASIC FUNCTIONS 95

12 6.2 WRITING BASIC FUNCTIONS 96

13 6.2 WRITING BASIC FUNCTIONS 97 Function Parameters Functions do not need to have parameters, but include parentheses. Parameters can be of type IN, OUT, or IN OUT (discussed later) For functions, you should use only IN parameters since function inherently returns a value. Define default values for parameters SQL Server: Must use DEFAULT keyword when calling functions. SQL Server: Default value assignment must be literal value, not expression or function.

14 6.2 WRITING BASIC FUNCTIONS 98

15 6.2 WRITING BASIC FUNCTIONS 99

16 6.3 INTEGRATION OF FUNCTIONS AND SQL 100 When using functions in SQL statements, use scalar-valued functions as column expressions or in WHERE clause. Typical applications of functions: Concatenation of data Complex SQL expressions that can be encapsulated in a function, for example last order for a given customer. Next example shows the latest pay raise for a give employee. Pay raise table is a child table of the employees table, storing pay raises over time for each employee. I want to see the latest pay raise for each employee.

17 6.3 INTEGRATION OF FUNCTIONS AND SQL 101

18 6.3 INTEGRATION OF FUNCTIONS AND SQL 102

19 6.3 INTEGRATION OF FUNCTIONS AND SQL 103 Calculate full compensation for each employee

20 6.3 INTEGRATION OF FUNCTIONS AND SQL 104

21 6.3 INTEGRATION OF FUNCTIONS AND SQL 105

22 6.4 ADVANCED FUNCTIONS 106 Functions can be set up in a recursive fashion, that means within the function s body the function is called again. Let us demonstrate this using factorials (5! = 1*2*3*4*5 = 120) Pseudo Code:

23 6.4 ADVANCED FUNCTIONS 107

24 6.4 ADVANCED FUNCTIONS 108

25 6.4 ADVANCED FUNCTIONS 109 Another example of a recursive function is calculating the next business day based on a user-supplied date. Weekend and holidays are to be skipped in order to find the next business day. Function will increment by one day and test whether this day is weekday and not a weekend or holiday. Start designing the steps: Think also about test cases during your design:

26 6.4 ADVANCED FUNCTIONS 110

27 6.4 ADVANCED FUNCTIONS 111