Query Design Center supports the following isolation levels for transactions:
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Read Committed
The Read Committed isolation level allows a transaction to acquire a read lock (if it only reads the data) or a write lock (if it updates or deletes data) on the current record of data with which it is working. The record being used by the transaction cannot be changed or removed by other transactions until the lock is released. Read locks are released when the transaction moves off the current record. Write locks are held until the transaction is committed or rolled back.
Transactions using the Read Committed isolation level wait until records of data that are write-locked by other transactions are unlocked before they acquire their own locks. Dirty reads are not possible. Nonrepeatable reads and phantom reads are possible.
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Read Uncommitted
The Read Uncommitted isolation level does not lock records. Dirty reads, nonrepeatable reads, and phantom reads are possible.
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Repeatable Read
The Repeatable Read isolation level places a shared lock on records. Dirty reads and nonrepeatable reads are not possible. Phantom reads are possible.
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Serializable
The Serializable isolation level locks an entire structure. Dirty reads, nonrepeatable reads, and phantom reads are not possible.
| Note: | If you do not specify an isolation level, the level Read Committed is applied to automatic and manual transactions. |
To set the isolation level for transactions, click the Options menu, point to Isolation Level, and click the level you want to apply to transactions.
A check mark appears to the left of the isolation level to indicate that it is enabled.
