СДЕЛКА. УПРАВЛЕНИЕ ТРАНЗАКЦИЯМИ. КОМАНДЫ РАЗДЕЛА TCL.

Аннотация

This article first introduces the concept of transactions and clearly explains about its commands. It clearly states when and under what conditions transaction orders are used. Also shown is the syntax of transaction commands. The differences between the commands are clearly highlighted. Keywords: Transaction, DDL, DML, DQL, DCL, TCL, COMMIT, ROLLBACK and SAVEPOINT. СДЕЛКА. УПРАВЛЕНИЕ ТРАНЗАКЦИЯМИ. КОМАНДЫ РАЗДЕЛА TCL. Аннотация. В этой статье впервые представлено понятие транзакций и подробно объяснены их команды. В нем четко указано, когда и при каких условиях используются ордера на транзакции. Также показан синтаксис команд транзакции. Различия между командами четко выделены. Ключевые слова: транзакция, DDL, DML, DQL, DCL, TCL, COMMIT, ROLLBACK и SAVEPOINT. SQL - Transaction Control (TCL) When using relational database management systems (RDBMSs) we often hear terms like DDL, DML, DQL, DCL, and TCL. 4 09 International scientific journal ISSN: 2181-3906 «MODERN SCIENCE АND RESEARCH» 2024 VOLUME 3 / ISSUE 3 / UIF:8.2 / MODERNSCIENCE.UZ In the context of SQL, TCL stands for Transaction Control Language. In SQL, TCL means Transaction Control and is a set of commands that manage the effectiveness of a DML action. TCL is a subset of SQL. It’s just one of the various initialisms we can find in SQL. Others include DDL (Data Definition Language), DML (Data Manipulation Language), DCL (Data Control Language), and DQL (Data Query Language). Transaction Control Language is a subset of SQL that’s used to manage transactions in a relational database. A transaction begins when the first executable SQL statement is encountered. An executable SQL statement is a SQL statement that generates calls to a database instance, including DML and DDL statements and the SET TRANSACTION statement. When a transaction begins, Oracle Database assigns the transaction to an available undo data segment to record the undo entries for the new transaction. A transaction ID is not allocated until an undo segment and transaction table slot are allocated, which occurs during the first DML statement. TCL commands are important for maintaining the consistency, integrity, and reliability of the database in the event of errors or failures during transactions. A transaction ID is unique to a transaction and represents the: undo segment number, slot, and sequence number. Transaction control involves using the following statements: The COMMIT statement ends the current transaction and makes all changes performed in the transaction permanent. COMMIT also erases all savepoints in the transaction and releases transaction locks. The ROLLBACK statement reverses the work done in the current transaction; it causes all data changes since the last COMMIT or ROLLBACK to be discarded. The ROLLBACK TO SAVEPOINT statement undoes the changes since the last savepoint but does not end the entire transaction. The SAVEPOINT statement identifies a point in a transaction to which you can later roll back. A commit ends the current transaction and makes permanent all changes performed in the transaction. 1. COMMIT When a transaction commits, the following actions occur: Purpose Use the COMMIT statement to end your current transaction and make permanent all changes performed in the transaction. A transaction is a sequence of SQL statements that Oracle Database treats as a single unit. This statement also erases all savepoints in the transaction and releases transaction locks. Until you commit a transaction: 4 10 International scientific journal ISSN: 2181-3906 «MODERN SCIENCE АND RESEARCH» 2024 VOLUME 3 / ISSUE 3 / UIF:8.2 / MODERNSCIENCE.UZ You can see any changes you have made during the transaction by querying the modified tables, but other users cannot see the changes. After you commit the transaction, the changes are visible to other users' statements that execute after the commit. You can roll back (undo) any changes made during the transaction with the ROLLBACK statement (see ROLLBACK). Oracle Database issues an implicit COMMIT under the following circumstances: Before any syntactically valid data definition language (DDL) statement, even if the statement results in an error After any data definition language (DDL) statement that completes without an error You can also use this statement to: Commit an in-doubt distributed transaction manually. Terminate a read-only transaction begun by a SET TRANSACTION statement. Oracle recommends that you explicitly end every transaction in your application programs with a COMMIT or ROLLBACK statement, including the last transaction, before disconnecting from Oracle Database. If you do not explicitly commit the transaction and the program terminates abnormally, then the last uncommitted transaction is automatically rolled back. A normal exit from most Oracle utilities and tools causes the current transaction to be committed. A normal exit from an Oracle precompiler program does not commit the transaction and relies on Oracle Databa