A column select expression is a select expression that specifies
    a one-column result table in one row and can be nested
    within predicates and (if they specify a single value) value
    expressions. Column select expressions cannot specify a list of
    select items. You can only specify one value in a select list.

    Column select expressions are also called scalar expressions.

    SQL accepts column select expressions as arguments to IN and
    quantified predicates, and more generally as value expressions.

    o  As arguments to IN and quantified predicates, column select
       expressions specify a collection of values to which SQL
       compares a value expression. Therefore, column select
       expressions as arguments to those predicates can return one
       or more values.

    o  As a type of value expression, column select expressions
       specify a single value. Therefore, a column select expression
       used as a value expression should not return more than one
       value. If it does, SQL generates the following error:

       %RDB-E-MULTIPLE_MATCH, record selection criteria should identify
                              only one record; more than one record found

       If a column select expression used as a value expression
       returns zero rows, SQL evaluates the value expression as null.
       The data type of a column select expression used as a value
       expression is the same as the data type of the column select
       expression's select item.

1  –  Environment

    You can use column select expressions in interactive SQL or in
    host language programs.

2  –  Format

  (B)0col-select-expr =          
                             
  qqq> select-expr qqqqqqq>  
                             

  (B)0select-expr =                                                     
                                                                    
  qwqwq>  select-clause  qqqqqqqqqqqqwqwqqqqqqk                     
   x tq> ( select-expr )  qqqqqqqqqqqu x      x                     
   x mq>   TABLE table-ref qqqqqqqqqqj x      x                     
   mqqqqqq select-merge-clause <qqqqqqqj      x
     lqqqqqqqqqqqqqqqqqqq <qqqqqqqqqqqqqqqqqqqj                     
     mqwqqqqqqqqqqqqqqqqqqqqwqqwqqqqqqqqqqqqqqqqqqwqqwqqqqqqqqqqqqqqqqqqqqwq>
       mq> order-by-clause qj  mq> offset-clause qj  mq> limit-to-clause qj

3  –  Arguments

3.1  –  select-expr

    A column select expression is a select expression specifying only
    one value in the select list. See Select_Expressions for more
    information.