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Deploying Crystal Reports

Introduction : Configuring the ODBC driver : Understanding transactions and isolation levels

Understanding transactions and isolation levels

SQL defines isolation levels in terms of the inconsistencies they allow:

The following table identifies which inconsistencies are either permitted or prevented by each isolation level.

Table 1. Transaction isolation levels
Isolation	Dirty read	Nonrepeatable read	Phantom read
READ UNCOMMITTED	Permitted	Permitted	Permitted
READ COMMITTED	Prevented	Permitted	Permitted
REPEATABLE READ	Prevented	Prevented	Permitted
SERIALIZABLE	Prevented	Prevented	Prevented

In this section:

Nonrepeatable read