-= (Subtract EQUALS) (Transact-SQL)
Applies To: SQL Server 2014, SQL Server 2016 Preview
Subtracts two numbers and sets a value to the result of the operation. For example, if a variable @x equals 35, then @x -= 2 takes the original value of @x, subtracts 2 and sets @x to that new value (33).
Applies to: SQL Server (SQL Server 2008 through current version), Azure SQL Database.
Is any valid expression of any one of the data types in the numeric category except the bit data type.
Returns the data type of the argument with the higher precedence. For more information, see Data Type Precedence (Transact-SQL).