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Chapter 17: Problem 20

Why is an explicit transaction end statement needed in SQL but not an explicit begin statement?

Short Answer

Expert verified
Certain commands in SQL implicitly start a new transaction, so an explicit 'BEGIN TRANSACTION' statement is not always needed. However, an explicit end statement such as COMMIT or ROLLBACK is required to either save the changes made during the transaction or to discard them. This maintains the data's consistency.

Step by step solution

01

Understanding SQL Transactions

SQL transactions group a set of tasks into a single unit of work. Transactions are used to make sure the data remains consistent. The unit of work within the transaction ensures either full completion or none at all, in case of any error.
02

Implicit Beginning of Transaction

In SQL, certain statements implicitly start a transaction. If a transaction is not already in progress, SQL starts a new transaction before any change-oriented SQL command such as INSERT, UPDATE, DELETE. So, explicit 'BEGIN TRANSACTION' statement is not a mandatory requirement before these commands.
03

Explicit End Of Transaction

The end of a SQL transaction is marked by a COMMIT or ROLLBACK statement. A COMMIT statement saves all of the modifications made since the start of a transaction. A ROLLBACK statement undoes any changes made since the start of the transaction. Without an explicit end statement, there's no clear indicator for SQL to either save or discard the changes, hence an explicit end statement is required.

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