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

Transcription

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

2 AGENDA 8. Using Declarative SQL in Procedural SQL 8.1 DML in Procedural SQL 8.2 Transaction Management 8.3 Autonomous Transactions

3 Procedural Database Programming (PL/SQL and T-SQL) 8. USING DECLARATIVE SQL IN PROCEDURAL SQL

4 8.1 DML IN PROCEDURAL SQL 153 Group multiple DML statements together into a logical transaction Apply the principle of all (commit) or nothing (rollback) ACID Principle: Brief Review of DML statements Generally no differences in syntax between Oracle and SQL Server

5 8.1 DML IN PROCEDURAL SQL 154 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

6 8.1 DML IN PROCEDURAL SQL 155 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: SQL Server: NOCOUNT

7 8.1 DML IN PROCEDURAL SQL 156

8 8.1 DML IN PROCEDURAL SQL 157

9 8.1 DML IN PROCEDURAL SQL 158 Returning information from DML statements Using non-procedural SQL statements in procedural environment generated the need to add extensions SELECT 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 global variable, not the best approach! SQL Server two new additional methods: 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

10 8.1 DML IN PROCEDURAL SQL 159 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

11 8.1 DML IN PROCEDURAL SQL 160

12 8.1 DML IN PROCEDURAL SQL 161

13 8.1 DML IN PROCEDURAL SQL 162

14 8.1 DML IN PROCEDURAL SQL 163

15 8.2 TRANSACTION MANAGEMENT 164 Transactions Transactions allow you as the developer to define the boundaries of an activity that will be considered atomic Start a transaction: Default Transaction Mode: 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:

16 8.2 TRANSACTION MANAGEMENT 165

17 8.2 TRANSACTION MANAGEMENT 166

18 8.2 TRANSACTION MANAGEMENT 167 Commit Statement The following rules apply after issuing a commit: A locks are released You cannot issue a rollback Rollback Statement Undo some or all of your changes

19 8.2 TRANSACTION MANAGEMENT 168 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

20 8.2 TRANSACTION MANAGEMENT 169

21 8.2 TRANSACTION MANAGEMENT 170

22 8.2 TRANSACTION MANAGEMENT 171

23 8.2 TRANSACTION MANAGEMENT 172

24 8.3 AUTONOMOUS TRANSACTIONS 173 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

25 8.3 AUTONOMOUS TRANSACTIONS 174 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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28 8.3 AUTONOMOUS TRANSACTIONS 177