| Function | A function returns a value.
Functions types include column functions, scalar
functions, row functions, or table functions. 
                                
                                    The argument of a column function is a collection of like
values (a column). This function can return a NULL value.The argument(s) of a scalar function are individual scalar
values, which can be of different types. This function can return a NULL value.The argument of a row function is a structured type. The
function returns a row of built-in data types and can only be
specified as a transform function for a structured type.The argument(s) of a table function are individual scalar
values, which can be of different types. The function returns a
table, and can be specified only within the FROM clause of a SELECT
statement. | 
                    
                        | CASE | CASE expressions allow an expression to be selected based on the evaluation of one or more conditions. A CASE expression contains one or more when clauses of either Search or Simple type. 
 
                                A Search CASE expression contains a condition that is evaluated, such as i<8.A Simple CASE expression determines if the  when clause  evaluates to true; otherwise, the else clause determines the value of the case-expression.  | 
                    
                        | CAST | A CAST function converts instances of a datatype to
instances of a different datatype. | 
                    
                        | Constant | A constant specifies a value: a string or a number. 
 
                                Numeric constants can be an integer, floating-point, or decimal. A string constant can be a character string, hexadecimal, or a host variable name. A colon precedes the host variable name, for example, :var. The host variable becomes a value when the statement is executed.  | 
                    
                        | Subquery | A subquery is a SELECT, WITH, or FULLSELECT statement nested within
another SQL statement. The expression value is the result of the
subquery. | 
                    
                        | Build up expressions by operators | You can build an expression by applying operators to columns or expressions such as x+y where x is a column and y is an expression. |