Stored procedures 1

Stored procedures and functions

Procedures and functions stored in the database

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Layered models vs. stored procedures

• Ordinary layered model– user interface– functions– model– data

• Layered model with stored procedures– user interface– functions in DB– model + data in DB

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Stored procedures / functions 313

• Stored procedures /functions are– Named blocks of PL/SQL

• SQL DDL• Assignments, if statements, loops, etc.

– Syntax checked and compiled into p-code• The p-code is stored in the database

• Stored procedures’ syntax– General syntax, page 314– Example, page 315

• Stored functions’ syntax– General syntax, page 319– Example fig. 14-6, page 321

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3 types of parameters, 314

• Procedures can have 3 types of parameters– IN

• used for input– OUT

• used for output• side effects hard to read / debug the code

– INOUT• used for input + output

– Examples• scottTigerStoredProcedures.sql

• Functions – standard: only IN parameters– Oracle: all kinds of parameters

• Don’t use OUT and INOUT with functions!

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Calling a stored procedure, 314

• Syntax– procedureName(formalParameter1, formalParameter2, …)– Examples page 314

• 2 ways to link formal and actual parameters– Position

• Like Java: 1st parameter formal parameter linked to 1st actual parameter, etc.

• Examples: – Figure 14-2, page 316– calling insertDept in scottTigerStoredProcedures.sql

– Named• Syntax: formalParameterName => value• Example: calling insertDept in scottTigerStoredProcedures.sql

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Some PL/SQL to use in the body of stored procedures and functions

• call pName(parameters)– call another procedure

• return value– return from a function

• variable := value– assignment

• begin … end– statement group

• if condition then statements else statements end if– Example page 329

• For loop• While loop• General loop

– Inner exit statement

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SQL statements• Stored procedures / functions can contain

SQL statements– select, insert, update, delete

• Select syntax [result: one value]– select attr into variable from …

• Example: searchDept, figure 14-4, page 318

• Insert example– insertDept (my own example)

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Cursors, 268

• Cursor points to the current row.– Very much like JDBC

• Example. totalSalary, fig. 14-3, page 317• DECLARE cName CURSOR FOR select

statement– declares the select statement– JDBC statement object

• OPEN cName– Executes the select statement– JDBC ResultSet rs = statement.executeQuery(…)

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Exception handling

• Stored procedures can handles exception– Similar to Java try … catch …– Syntax page 314– Example search_emp + searchDept, fig. 14-4, page

318– Fig. 12-7, page 282 Predefined/named system

exceptions– When others

• Catches exceptions not already caught– General strategy

• Don’t catch exceptions if you don’t know how to handle them properly

• Writing to the screen is usually not enough

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Calling a function, 320

• Functions can be called from – PL/SQL block (like the body of another

procedure / function)• Example fig. 14-7, page 321

– SQL statement• Example page 323

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Compiling and recompiling stored procedures, 317

• Stored procedures / functions are automatically compiled when recreated.

• If one of the tables used in a procedures is altered the procedure / function must be recompiled– Alter procedure procedureName compile;

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Packages, 323

• A packages groups a set of logically connected stored procedures, functions, etc.– Kind of module

• Built-in packages in Oracle– STANDARD

• Many functions used in Oracle

– DBMS_OUTPUT• Put_line and other procedures• Example fig. 14-7, page 321

• You can create your own packages!

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Package structure, 324

• Package specification– Specification of procedures, functions, etc.

• Public part of the package• Syntax page 324• Example fig. 14-10, page 325

• Package body– Implementation of procedures, functions, etc.

• Private part of the package• Syntax page 325• Example fig. 14-11, page 327

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Calling a procedure / function in a package, 326

• Name of procedure / function must be prefixed with the name of the package– PackageName.ProcedureName(…)– DBMS_OUTPUT.PUT_LINE(…)– myPackage.myProcedure(…)– Example fig. 14-12, page 328

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Java JDBC API

• Pakken java.sql– interface CallableStatement– "factoried" by a connection object

• CallableStatement prepareCall(String sql)• cst = prepareCall("{call insertDept(?, ?, ?)}");

– CallableStatement extends PreparedStatement

• PreparedStatement extends Statement

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JDBC examples

• Stored procedure with IN parameters

• Stored procedure with IN and OUT parameters

• Stored function– CallableStatementExample.java

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Handling parameters

• IN parameters– handled like parameters to prepared

statements• cstm.setString(1, 'Anders');• cstm.setXxx(position, value);

• OUT parameters + results from functions– register type before executing the call

• cstm.registerOutParameter(position, type)

– results can be obtained after executing the call• value = cstm.getXxx(position)