Selected columns ( select column ) must be specified in a QUERY specification (query spec) or a QUERY specification (named query spec) to specify a result table.

The sequence of selected columns defines the columns in the result table. The columns in the result table are produced from the columns of the temporary result table and by the rowno columns or stamp columns, if these exist. The columns of the temporary result table are determined by the FROM clause of the table expression. The order of the column names in the temporary result table is determined by the order of the table names in the FROM clause.

<table columns> ::= * | <table name>.* | <reference name>.*
<derived column> ::= <expression> [ [AS] <result column name>] | <result column name> = <expression>
<rowno column> ::= ROWNO [<result column name>] | <result column name> = ROWNO
<stamp column> ::= STAMP [<result column name>] | <result column name> = STAMP

<result column name> ::= <identifier>
table name, reference name, expression, identifier

Every column name that is specified as a selected column must uniquely denote a column in a QUERY specification (query spec) of the underlying tables. If necessary, the column name must be qualified with the table name.

The specification of a column with the data type LONG in a selected column is only valid in the uppermost sequence of select columns in a QUERY statement, SINGLE SELECT statement, SELECT DIRECT statement, or a SELECT ORDERED statement if the DISTINCT specification was not used there.

The specification of a column with the data type LONG in a selected column is only valid in the uppermost sequence of select columns in a CREATE VIEW statement which is based on exactly one base table.

If a selected column contains a set function (set function spec), the sequence of selected columns to which the selected column belongs must not contain any table columns, and every column name occurring in an expression must denote a grouping column, or the expression must consist of grouping columns.

• Specifying table columns in a selected column is a quick way of specifying the result table columns.

• Specifying a selected column of the type * is a quick way of specifying all temporary result table columns.
  Columns for which the user has not the SELECT privilege and the implicitly generated column SYSKEY are not passed.
• Specifying <table name>.* or <reference name>.* is quick way of specifying all the columns in the underlying table. The first column name of the result table is taken from the first column name of the underlying table, the second column name of the result table corresponds to the second column name of the underlying table, etc. The order of column names in the underlying table corresponds to the order determined when the underlying table is defined.
  Columns for which the user has not the SELECT privilege and the implicitly generated column SYSKEY are not passed.

• Specifying derived column in a selected column defines a column in the result table. If a column of the result table has the form <expression> [AS] <result column name> or the form <result column name> = <expression> , this result column receives the name result column name .
  If no <result column name> is specified and the expression is a column specification that denotes a column in the temporary result table, the column in the result table receives the column name of the temporary result table.
  If no <result column name> is specified and the expression is not a column specification, the column receives the name EXPRESSION_ , where "_" denotes a number with a maximum of three digits, starting with EXPRESSION1 , EXPRESSION2 , etc.
• A ROWNO column may only be used in a selected column that belongs to a QUERY statement.
  If a rowno column is specified, a column with the data type FIXED(10) is generated with the name ROWNO. It contains the values 1, 2, 3,... which the numbers of the result table rows.
  If the ROWNO column was specified in the form ROWNO <result column name> or the form <result column name> = ROWNO , this result column receives the name result column name .
  A rowno column>must not be ordered by using ORDER BY.
• A STAMP column may only be specified in a selected column that belongs to a QUERY- expression of an INSERT statement.
  The database system is able to generate unique values. This is a serial number that starts with X'000000000001'. The values are assigned in ascending order. It cannot be ensured that a sequence of values is uninterrupted.
  If a stamp column is specified, the next value of the data type CHAR(8) BYTE generated by the database system is produced for each row in the temporary result table.

Each column of a result table has exactly the same data type, the same length, the same precision, and the same scale as the derived column or the column underlying the table columns.

This does not apply to the data types DATE and TIMESTAMP. To enable the representation of any date and time format, the length of the result table column is set to the maximum length required for the representation of a date value (length 10) or a timestamp value (length 26).