ANSI_WARNINGS

SET ANSI_WARNINGS { ON | OFF }

• When set to ON, if null values appear in aggregate functions, such as SUM, AVG, MAX, MIN, STDEV, STDEVP, VAR, VARP, or COUNT, a warning message is generated. 
• When set to OFF, no warning is issued.

• When set to ON, the divide-by-zero and arithmetic overflow errors cause the statement to be rolled back and an error message is generated. 
• When set to OFF, the divide-by-zero and arithmetic overflow errors cause null values to be returned.

Notes:

1. SET ANSI_WARNINGS must be ON when you are creating or manipulating indexes on computed columns or indexed views.
2. ANSI_WARNINGS should be set to ON for executing distributed queries.

http://msdn.microsoft.com/en-us/library/ms190368.aspx