NULL(4)                                             Linux Programmer's Manual                                            NULL(4)



NAME
       null, zero - data sink

DESCRIPTION
       Data written to a null or zero special file is discarded.

       Reads  from  the  null  special  file always return end of file (i.e., read(2) returns 0), whereas reads from zero always
       return bytes containing zero (\0 characters).

       null and zero are typically created by:

              mknod -m 666 /dev/null c 1 3
              mknod -m 666 /dev/zero c 1 5
              chown root:root /dev/null /dev/zero

FILES
       /dev/null
       /dev/zero

NOTES
       If these devices are not writable and readable for all users, many programs will act strangely.

SEE ALSO
       chown(1), mknod(1), full(4)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2009-02-23                                                    NULL(4)
VALUES(7)                                                 SQL Commands                                                 VALUES(7)



NAME
       VALUES - compute a set of rows


SYNOPSIS
       VALUES ( expression [, ...] ) [, ...]
           [ ORDER BY sort_expression [ ASC | DESC | USING operator ] [, ...] ]
           [ LIMIT { count | ALL } ]
           [ OFFSET start [ ROW | ROWS ] ]
           [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]


DESCRIPTION
       VALUES  computes  a row value or set of row values specified by value expressions. It is most commonly used to generate a
       ``constant table'' within a larger command, but it can be used on its own.

       When more than one row is specified, all the rows must have the same number of elements. The data types of the  resulting
       table's  columns  are determined by combining the explicit or inferred types of the expressions appearing in that column,
       using the same rules as for UNION (see in the documentation).

       Within larger commands, VALUES is syntactically allowed anywhere that SELECT is. Because it is treated like a  SELECT  by
       the  grammar,  it  is possible to use the ORDER BY, LIMIT (or equivalently FETCH FIRST), and OFFSET clauses with a VALUES
       command.

PARAMETERS
       expression
              A constant or expression to compute and insert at the indicated place in the resulting table (set of rows).  In  a
              VALUES list appearing at the top level of an INSERT, an expression can be replaced by DEFAULT to indicate that the
              destination column's default value should be inserted. DEFAULT cannot be used when VALUES appears  in  other  con-
              texts.

       sort_expression
              An expression or integer constant indicating how to sort the result rows. This expression can refer to the columns
              of the VALUES result as column1, column2, etc. For more details see ORDER BY Clause [select(7)].

       operator
              A sorting operator. For details see ORDER BY Clause [select(7)].

       count  The maximum number of rows to return. For details see LIMIT Clause [select(7)].

       start  The number of rows to skip before starting to return rows.  For details see LIMIT Clause [select(7)].

NOTES
       VALUES lists with very large numbers of rows should be avoided, as you might encounter  out-of-memory  failures  or  poor
       performance.   VALUES  appearing  within  INSERT  is  a special case (because the desired column types are known from the
       INSERT's target table, and need not be inferred by scanning the VALUES list), so it can  handle  larger  lists  than  are
       practical in other contexts.

EXAMPLES
       A bare VALUES command:

       VALUES (1, 'one'), (2, 'two'), (3, 'three');

       This will return a table of two columns and three rows. It's effectively equivalent to:

       SELECT 1 AS column1, 'one' AS column2
       UNION ALL
       SELECT 2, 'two'
       UNION ALL
       SELECT 3, 'three';


       More usually, VALUES is used within a larger SQL command.  The most common use is in INSERT:

       INSERT INTO films (code, title, did, date_prod, kind)
           VALUES ('T_601', 'Yojimbo', 106, '1961-06-16', 'Drama');


       In the context of INSERT, entries of a VALUES list can be DEFAULT to indicate that the column default should be used here
       instead of specifying a value:

       INSERT INTO films VALUES
           ('UA502', 'Bananas', 105, DEFAULT, 'Comedy', '82 minutes'),
           ('T_601', 'Yojimbo', 106, DEFAULT, 'Drama', DEFAULT);


       VALUES can also be used where a sub-SELECT might be written, for example in a FROM clause:

       SELECT f.*
         FROM films f, (VALUES('MGM', 'Horror'), ('UA', 'Sci-Fi')) AS t (studio, kind)
         WHERE f.studio = t.studio AND f.kind = t.kind;

       UPDATE employees SET salary = salary * v.increase
         FROM (VALUES(1, 200000, 1.2), (2, 400000, 1.4)) AS v (depno, target, increase)
         WHERE employees.depno = v.depno AND employees.sales >= v.target;

       Note that an AS clause is required when VALUES is used in a FROM clause, just as is true for SELECT. It is  not  required
       that  the  AS  clause  specify names for all the columns, but it's good practice to do so.  (The default column names for
       VALUES are column1, column2, etc in PostgreSQL, but these names might be different in other database systems.)

       When VALUES is used in INSERT, the values are all automatically coerced to the data type of the corresponding destination
       column.  When it's used in other contexts, it might be necessary to specify the correct data type. If the entries are all
       quoted literal constants, coercing the first is sufficient to determine the assumed type for all:

       SELECT * FROM machines
       WHERE ip_address IN (VALUES('192.168.0.1'::inet), ('192.168.0.10'), ('192.168.1.43'));


              Tip: For simple IN tests, it's better to rely on the list-of-scalars form of IN than to write a  VALUES  query  as
              shown above. The list of scalars method requires less writing and is often more efficient.


COMPATIBILITY
       VALUES conforms to the SQL standard.  LIMIT and OFFSET are PostgreSQL extensions; see also under SELECT [select(7)].

SEE ALSO
       INSERT [insert(7)], SELECT [select(7)]



SQL - Language Statements                                  2011-09-22                                                  VALUES(7)