The least strict isolation level, where reads acquire no shared locks (as if every table had a NOLOCK hint), leaving the door open to dirty reads, non-repeatable reads and phantoms.
Read more: Microsoft Learn
In the Ultra Transcenders books
Each book explains READ UNCOMMITTED in context, with comparison tables and the common traps.
Terms in this definition
- LEAST
Pass up to 254 expressions to this T-SQL function and it hands back whichever is smallest. Both Fabric Warehouse and SQL analytics endpoints support it.
- Isolation level
Chosen with SET TRANSACTION ISOLATION LEVEL, this determines how much one transaction can see of, or be affected by, concurrent work. The levels range from READ UNCOMMITTED and READ COMMITTED through REPEATABLE READ to SNAPSHOT and SERIALIZABLE.
- WHERE
Limits a SELECT, UPDATE or DELETE to just the rows meeting a condition. Omit it, and the statement hits every row.
- Event
Table in Log Analytics where entries from Windows event logs are kept.
- NOLOCK
Using this hint on a table means no shared locks are requested, mirroring READ UNCOMMITTED; as a result a query can pick up dirty, non-repeatable or phantom data.