Enum to specify transaction isolation level
TRANSACTION_NONE: Transactions are not supported.
TRANSACTION_READ_UNCOMMITTED: Data with uncommitted changes can be read from other transactions.
TRANSACTION_READ_COMMITTED: Only committed changes can be read from other transactions.
TRANSACTION_REPEATABLE_READ: Ensure that the same query always returns the same results, unaffected by changes from other transactions.
TRANSACTION_SERIALIZABLE: Transactions are treated as if they are serialized to each other to guarantee data integrity.