MySQL Transactions
What are transactions?
# Sequential
group of DML statements, which is performed as if it were one
single work unit.
# Will never complete unless each
individual operation within the group is sucessful.If any operation within the
transaction fails, the entire transaction will fail.
#
Begins with the first executable SQL statement.
# Ends when
it is committed or rolled back, either explicitly with a COMMIT or ROLLBACK
statement or implicitly when a DDL statement
is issued.
Sample Scenario
Suppose a bank customer transfers money from his savings account
(SB a/c) to his current account (CA a/c), the statement will be divided into
four blocks:
# Debit SB a/c
# Credit CA a/c
# Record in Transaction
Journal.
# End Transaction
The SQL statement to debit SB a/c is as follows:
UPDATE sb_accounts SET balance = balance - 500 WHERE account_no =
932656;
The SQL statement to credit CA a/c is as follows:
UPDATE ca_accounts SET balance = balance + 500 WHERE account_no =
933456;
The SQL statement for recording in the transaction journal is as
follows:
INSERT INTO journal VALUES (100896, 'Transaction on Kumar Atul
Jaiswal a/c', '28-NOV-11' 932656, 933456, 500);
The SQL statement for End Transaction is as follows:
COMMIT WORK;
Ensures that all operations within the work unit are completed successfully;
otherwise, the transaction is aborted at the point of failure and previous
operations are rolled back to their former state.
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