Difference between EXEC & EXECUTE()

EXECUTE

 The EXECUTE, or EXEC statement executes a stored procedure by following the command with the name of the stored procedure and any proper parameter arguments:

 EXEC sp_Empfind @City='DE'

EXECUTE()

 The EXECUTE(character_string) function executes a character string containing a Transact-SQL command.

 It can be written like EXEC(character_string) also. The EXECUTE(character_string) function is not compiled until run time and the generated plan is not cached and reused. The following example executes a dynamic string that concatenates literal strings with variable values:

 DECLARE @mycol varchar(30)

 DECLARE @mytable varchar(30)

 SELECT @mycol = 'EMPID'

 SELECT @mytable = 'Employee'

 EXEC('SELECT ' + @mycol + ' FROM ' + @mytable)

see also : sp_execute of pl sql