Transcript Stored procedures

Stored procedures and
functions
Procedures and functions stored
in the database
Stored procedures
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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
• 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
• Function
– Returns a result
• Procedure
– Does not return a result
– Comparable to a void method in C# or Java
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3 types of parameters
• 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
• Syntax
– procedureName(formalParameter1, formalParameter2, …)
• 2 ways to link formal and actual parameters
– Position
• Like Java: 1st parameter formal parameter linked to 1st actual
parameter, etc.
– Named
• Syntax: formalParameterName => value
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Some PL/SQL to use in the body of
stored procedures and functions
• call pName(parameters) • begin … end
– call another procedure
• return value
– return from a function
• variable := value
– assignment
– statement group
• if condition then
statements else
statements end if
• 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 …
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Cursors
• 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)
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