Class 6 - ucb

Instructor: Michael Kremer, Ph.D.
Technology & Information Management
Class 6
Database Programming
PROCEDURAL DATABASE PROGRAMMING
( PL/SQL AND T-SQL)
AGENDA
8. Using Declarative SQL in Procedural SQL
8.1 DML in Procedural SQL
8.2 Transaction Management
8.3 Autonomous Transactions
Procedural Database Programming (PL/SQL and T-SQL)
8. USING DECLARATIVE SQL IN PROCEDURAL
SQL
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8.1 DML IN PROCEDURAL SQL
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Group multiple DML statements together into a logical
transaction.
Apply the principle of all (commit) or nothing (rollback).
ACID Principle:
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Atomicity: A transaction’s changes to a state are atomic, either all or none
take place.
Consistency: Data before and after the transaction is in consistent state
(but not necessarily during the transaction)
Isolation: Changes resulting from a transaction are isolated from other
sessions until a commit or rollback occurs.
Durability: Once changes are made permanent, they are persistent forever
in the database.
Brief Review of DML statements.
Generally no differences in syntax between Oracle and SQL
Server.
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8.1 DML IN PROCEDURAL SQL
Insert Statement
 Two main variations.
 Optional column list allows
you to specify only those
columns that you want to
provide values for.
Update Statement
 Where clause is optional,
if left out, entire table is
updated.
Delete Statement
 Where clause is optional,
if left out, all rows are deleted
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8.1 DML IN PROCEDURAL SQL
Other DML statements: Specialized statements for particular
data situations, such as Merge.
Attributes for DML statements
 Information about the most recent DML statement is available in
both platforms.
 For example, you may want to know how many rows were
affected.
 Oracle:
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SQL Server:
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SET NOCOUNT ON|OFF
@@ROWCOUNT
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8.1 DML IN PROCEDURAL SQL
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8.1 DML IN PROCEDURAL SQL
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8.1 DML IN PROCEDURAL SQL
Returning information from DML statements
 Using non-procedural SQL statements in procedural environment
generated the need to add extensions.
 For example, a SELECT statement allows you to store returned column
values in variables.
 For insert statements, store values of automatically generated data,
such as sequences/identity columns in a variable.
 This is necessary to insert a corresponding child record!
 SQL Server: @@Identity global variable, not the best approach!
 SQL Server two new additional methods:
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IDENT_CURRENT(‘table_name’), SCOPE_IDENTITY
In Oracle, use another select statement to find out about the most
recent sequence number.
Safest way to retrieve the primary key value is to issue a SELECT
statement and use the logical key of the row that was inserted in the
WHERE clause to uniquely identify the row.
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8.1 DML IN PROCEDURAL SQL
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Best way is to be able to retrieve the primary key value when
using the insert statement.
Returning clause in Oracle:
Output Inserted into in SQL Server:
Need to declare a table
variable.
Allows to store multiple columns
in one variable.
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8.1 DML IN PROCEDURAL SQL
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8.1 DML IN PROCEDURAL SQL
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8.1 DML IN PROCEDURAL SQL
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8.1 DML IN PROCEDURAL SQL
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8.2 TRANSACTION MANAGEMENT
Transactions
 Transactions allow you as the developer to define the
boundaries of an activity that will be considered atomic.
 Start a transaction:
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Default Transaction Mode:
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SQL Server: Issue Begin Tran statement
Oracle: Simply issue DML statement
SQL Server: Autocommit. When statement completes successfully, it is
committed otherwise is it rolled back.
Oracle: You have to issue either Commit or Rollback
Change SQL Server’s default behavior:
SET IMPLICIT_TRANSACTIONS ON;
ALTER DATABASE db_name SET READ_COMMITTED_SNAPSHOT ON;
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8.2 TRANSACTION MANAGEMENT
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8.2 TRANSACTION MANAGEMENT
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8.2 TRANSACTION MANAGEMENT
Commit Statement

The following rules apply after issuing a commit:

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A locks are released
You cannot issue a rollback
Rollback Statement
 Undo some or all of your changes
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8.2 TRANSACTION MANAGEMENT
Savepoint/Save Statement
 SAVEPOINT gives a name to, and marks a point in, the
processing of your transaction allowing you
 To ROLLBACK To that point, undoing any changes and releasing
any locks issued after that savepoint
 Preserve any changes and locks that occurred before you
marked the savepoint.
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8.2 TRANSACTION MANAGEMENT
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8.2 TRANSACTION MANAGEMENT
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8.2 TRANSACTION MANAGEMENT
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8.2 TRANSACTION MANAGEMENT
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8.3 AUTONOMOUS TRANSACTIONS
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Autonomous transactions are started by a parent, or main,
transaction but operate independently of the parent for
transaction control.
Commit, rollback or failure in either transaction does not impact
the other
transaction.
Only in Oracle, you
can simulate this
in SQL Server.
Oracle:
PRAGMA AUTONOMOUS_TRANSACTION
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8.3 AUTONOMOUS TRANSACTIONS
Applications for autonomous transactions:
 Logging mechanism: You want to rollback your main transaction
when an error occurs, yet you want to record the error info.
 Perform commits and rollbacks in your database triggers:
Commit or rollback in triggers irrespective of main transaction.
 Reusable application components: Build completely
independent units of functionality, especially in web apps.
 Call user-defined functions in SQL that modify tables: In Oracle
only, you can declare a function as an autonomous transaction,
perform DML statements while running it in a SQL Select
statement.
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8.3 AUTONOMOUS TRANSACTIONS
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8.3 AUTONOMOUS TRANSACTIONS
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8.3 AUTONOMOUS TRANSACTIONS