       4.8  Columns

A column is a multiset of values that may vary over time. All
values of the same column are of the same data type or domain and
are values in the same table. A value of a column is the smallest
unit of data that can be selected from a table and the smallest unit
of data that can be updated.

         A column is described by a column descriptor. A column descriptor
         includes:

       -  the name of the column;


         -  if the column is based on a domain, then the name of that do-
            main; otherwise, the data type descriptor of the data type of
            the column;


         -  the ordinal position of the column within the table that con-
            tains the column.



         4.9  Tables

         The row is the smallest unit of data that can be inserted into a
         table and deleted from a table.


         
The degree of a table is the number of columns of that table. At any time,
the degree of a table is the same as the cardinality of each of its rows
and the cardinality of a table is the same as the cardinality of each of
its columns. A table whose cardinality is 0 is said to be empty. A table
is either a base table, a viewed table, or a derived table. A base table
is either a persistent base table, a global tempo- rary table, a created
local temporary table, or a declared local temporary table.

         
A viewed table is a named derived table defined by a <view definition>. A
viewed table is sometimes called a view.


         Every table descriptor includes:

         -  the degree of the table (the number of column descriptors);
and

         -  the column descriptor of each column in the table.





         
A cursor in the open state identifies a table, an ordering of the rows of
that table, and a position relative to that ordering.





        An SQL-session has context that is preserved when an SQL-session
         is made dormant and restored when the SQL-session is made
current.
         This context comprises:

         -  the current SQL-session identifier,

         -  the current <authorization identifier>,

         -  the identities of all instances of temporary tables,

         -  the SQL-session <module>,

         -  the current default catalog name,

         -  the current default unqualified schema name,

         -  the current character set name substitution value,

         -  the current default time zone,

         -  the current constraint mode for each integrity constraint,

         -  the current transaction access mode,

         -  the cursor position of all open cursors,

         -  the contents of all SQL dynamic descriptor areas,

         -  the current transaction isolation level, and

         -  the current transaction diagnostics area limit.









         In each catalog in an SQL-environment, there is a schema, the
         Information Schema, with the name INFORMATION_SCHEMA, contain-
         ing a number of view descriptors, one base table descriptor ,
         and several domain descriptors. The data accessible through these
         views is a representation of all of the descriptors in all of the
         schemas in that catalog.

         <reserved word> ::=
                ABSOLUTE | ACTION | ADD | ALL | ALLOCATE | ALTER | AND
              | ANY | ARE | AS | ASC
              | ASSERTION | AT | AUTHORIZATION | AVG
              | BEGIN | BETWEEN | BIT | BIT_LENGTH | BOTH | BY
              | CASCADE | CASCADED | CASE | CAST | CATALOG | CHAR |
CHARACTER |
 CHAR_
              LENGTH
              | CHARACTER_LENGTH | CHECK | CLOSE | COALESCE | COLLATE |
COLLATI
ON

              | COLUMN | COMMIT | CONNECT | CONNECTION | CONSTRAINT
              | CONSTRAINTS | CONTINUE
              | CONVERT | CORRESPONDING | COUNT | CREATE | CROSS | CURRENT
              | CURRENT_DATE | CURRENT_TIME | CURRENT_TIMESTAMP | CURRENT_
              USER | CURSOR
              | DATE | DAY | DEALLOCATE | DEC | DECIMAL | DECLARE |
DEFAULT | D
EFERRABLE

              | DEFERRED | DELETE | DESC | DESCRIBE | DESCRIPTOR |
DIAGNOSTICS

              | DISCONNECT | DISTINCT | DOMAIN | DOUBLE | DROP
              | ELSE | END | END-EXEC | ESCAPE | EXCEPT | EXCEPTION
              | EXEC | EXECUTE | EXISTS
              | EXTERNAL | EXTRACT
              | FALSE | FETCH | FIRST | FLOAT | FOR | FOREIGN | FOUND |
FROM |
FULL
                                                                 (p203 of
1498)
              | GET | GLOBAL | GO | GOTO | GRANT | GROUP
              | HAVING | HOUR
              | IDENTITY | IMMEDIATE | IN | INDICATOR | INITIALLY | INNER
| INP
UT

              | INSENSITIVE | INSERT | INT | INTEGER | INTERSECT |
INTERVAL | I
NTO | IS

              | ISOLATION
              | JOIN
              | KEY
              | LANGUAGE | LAST | LEADING | LEFT | LEVEL | LIKE | LOCAL |
LOWER

              | MATCH | MAX | MIN | MINUTE | MODULE | MONTH
              | NAMES | NATIONAL | NATURAL | NCHAR | NEXT | NO | NOT |
NULL

              | NULLIF | NUMERIC
              | OCTET_LENGTH | OF | ON | ONLY | OPEN | OPTION | OR
              | ORDER | OUTER
              | OUTPUT | OVERLAPS


                                                                 (p204 of
1498)
              | PAD | PARTIAL | POSITION | PRECISION | PREPARE | PRESERVE
| PRI
MARY

              | PRIOR | PRIVILEGES | PROCEDURE | PUBLIC
              | READ | REAL | REFERENCES | RELATIVE | RESTRICT | REVOKE |
RIGHT

              | ROLLBACK | ROWS
              | SCHEMA | SCROLL | SECOND | SECTION | SELECT | SESSION |
SESSION
_
              USER | SET
              | SIZE | SMALLINT | SOME | SPACE | SQL | SQLCODE | SQLERROR
| SQL
STATE

              | SUBSTRING | SUM | SYSTEM_USER
              | TABLE | TEMPORARY | THEN | TIME | TIMESTAMP | TIMEZONE_
              HOUR | TIMEZONE_MINUTE
              | TO | TRAILING | TRANSACTION | TRANSLATE | TRANSLATION |
TRIM |
TRUE

              | UNION | UNIQUE | UNKNOWN | UPDATE | UPPER | USAGE | USER |
USIN
G

              | VALUE | VALUES | VARCHAR | VARYING | VIEW
              | WHEN | WHENEVER | WHERE | WITH | WORK | WRITE
              | YEAR
              | ZONE




