Transaction in Oracle Database

The transactions

Managing transactions is at the heart of database processing. To allow multiple users to access it simultaneously, the DBMS must manage transactions with the minimum of conflicts while ensuring the consistency of the database.

A transaction is a logical unit made up of one or more SQL statements.

DML command 1
DML command 2
................................
................................
................................
DML command n

A transaction begins implicitly with the execution of the first SQL command and ends with a COMMIT to commit or a ROLLBACK to roll back the transaction.

The transaction continues executing SQL commands one at a time until one of the following occurs:

    COMMIT: Transaction encounters an explicit COMMIT statement, all changes made to the database up to this point are committed.

    ROLLBACK: Transaction encounters an explicit ROLLBACK statement, all changes made to the database up to this point are rolled back.

  DML instruction: If an DDL instruction is encountered such as CREATE, DROP, RENAME, or ALTER, Oracle first commits the current DML instructions for the transaction and then executes and commits the DDL instruction in question. This is an implied commit.

    Normal end of the calling program: if the program ends without errors, the transaction is committed implicitly. This is the case when you use the sqlplus tool, then you enter a series of DML commands in interactive mode, then you exit the session normally via the sqlplus "EXIT" command. In this case an implicit commit is applied to your transaction.

    Abnormal program termination: Such as a network cut or a program kill, the transaction is implicitly rolled back.


Learning Oracle DBA is not too short and quick guide. You should need to read several books and Oracle documentation for understanding of depth of each topics. You can get more tips and tutorials for Oracle database administration from our other resources like this or this.

PL/SQL For Oracle DBA

PL / SQL language

PL / SQL is a procedural language specific to Oracle which constitutes an extension to the SQL language (non-procedural language).

SQL commands can be embedded within PL / SQL code. These commands are called Embedded SQL Commands.

PL / SQL code can be used in program units stored in the database such as procedures, functions, and packages (groups of procedures and functions). These program units are said to be stored.

If these procedures are not stored in the database but incorporated into an application (development tools such as Oracle FORMS DEVELOPER and Oracle REPORT DEVELOPER), they are called application procedures.

PL / SQL code embedded in an application program unit or stored but not named is called an anonymous block. An anonymous block which does not have a name, therefore, cannot be stored in the database.

The advantage of a stored unit of programs is that it can be called by name from your application code and Oracle stores the result of the parse analysis of the unit in the database (persistent storage on disk). Considerable performance gains are generated as the parse output is made available and persistent for future reuse of unit code.

Example of PL / SQL code:

DECLARED
numerator NUMBER;
denominator NUMBER;
the_ratio NUMBER;
lower_limit CONSTANT NUMBER: = 0.72;
samp_num CONSTANT NUMBER: = 132;

BEGIN
SELECT x, y INTO numerator, denominator FROM result_table
WHERE sample_id = samp_num;

the_ratio: = numerator / denominator;

IF the_ratio> lower_limit THEN
INSERT INTO ratio VALUES (samp_num, the_ratio);

ELSE
INSERT INTO ratio VALUES (samp_num, -1);
END IF;

COMMIT;

EXCEPTION
WHEN ZERO_DIVIDE THEN
INSERT INTO ratio VALUES (samp_num, 0);
COMMIT;
WHEN OTHERS THEN
ROLLBACK;

END;

Explanations:

This PL / SQL code declares several variables and constants, then calculates a ratio value (the_ratio) for values ​​(numerator, denominator) selected from a table (result_table).

Very few times, Oracle DBA needs to address about PL/SQL because there are developers available for every company to utilize this PL/SQL for making forms and reports. Understanding PL/SQL is essential for Oracle database administrators. Stay connected with our blog for getting more advance knowledge of Oracle DBA tips and Tutorials.

SQL language for Oracle DBA

SQL language

SQL is a standard non-procedural language for relational database management systems (RDBMS)

Examples of SQL queries:

    SELECT ename FROM emp;
    SELECT last_name, department_id FROM employees;
    DELETE FROM department WHERE department_id IN (10, 30, 70);
    CREATE TABLE articles (article_id VARCHAR2 (15), designation VARCHAR2 (40));
    INSERT INTO articles VALUES (‘imp1’, laser printer ’);
    DROP TABLE articles;
    GRANT SELECT ON department TO scott;
    REVOKE DELETE ON department FROM scott;

The terms SELECT, FROM, DELETE, WHERE, IN, CREATE, TABLE, VARCHAR2, INSERT, INTO, VALUES, DROP, GRANT, TO, REVOKE, ON are words reserved for SQL

Oracle SQL statements are classified into categories:

  DML commands for Data Manipulation Language (SELECT, INSERT, UPDATE, DELETE)
    DDL commands for Data Definition Language (CREATE, ALTER, DROP, RENAME, TRUNCATE, GRANT, REVOKE…).
        DDL commands are automatically validated: they generate an implicit commit.
    Control Commands of:
        Transactions (COMMIT, ROLLBACK, SAVEPOINT, SET TRANSACTION)
        Sessions (ALTER SESSION)
        and System (ALTER SYSTEM)

SQL Recursive commands:

When an DDL command is issued, Oracle automatically issues an LMD command to modify the corresponding information in the data dictionary. This last command is called a recursive SQL command.

An DDL "CREATE TABLE" command, for example, issued by a user to create a table in their own schema, automatically generates another recursive LMD command (INSERT) in the SYS schema: data dictionary tables. In fact, the information on the structure of the newly created table must be inserted and available in the data dictionary.


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