This section contains special considerations concerning Natural data manipulation language (DML) statements (that is, Natural native DML statements and Natural SQL DML statements), and Natural system variables when used with SQL/DS
It mainly consists of information also contained in the Natural basic documentation set where each Natural statement and variable is described in detail.
For an explanation of the symbols used in this section to describe the syntax of Natural statements, see Syntax Symbols in the Natural Statements documentation.
For information on logging SQL statements contained in a Natural program, refer to DBLOG Trace Screen for SQL Statements in the DBLOG Utility documentation.
This section covers the following topics:
This section summarizes particular points you have to consider when using Natural native data manipulation language (DML) statements with SQL/DS. Any Natural statement not mentioned in this section can be used with SQL/DS without restriction.
Below is information on the following Natural DML statements:
The Natural native DML statement BACKOUT TRANSACTION undoes all
database modifications made since the beginning of the last logical
transaction. Logical transactions can start either after the beginning of a
session or after the last SYNCPOINT,
END TRANSACTION, or
BACKOUT TRANSACTION statement.
How the statement is translated and which command is actually issued depends on the environment:
Under CICS, the BACKOUT TRANSACTION statement is
translated into an EXEC CICS ROLLBACK command.
However, in pseudo-conversational mode, only changes made to the database since
the last terminal I/O are undone. This is due to CICS-specific transaction
processing, see Natural for
DB2 under CICS.
In batch mode, the BACKOUT
TRANSACTION statement is translated into an SQL
ROLLBACK command.
Note:
Be aware that with terminal input in SQL/DS database loops, Natural
switches to conversational mode if no file server is used.
As all cursors are closed when a logical unit of work ends, a
BACKOUT TRANSACTION statement must not be placed within a database
loop; instead, it has to be placed outside such a loop or after the outermost
loop of nested loops.
If an external program written in another standard programming language
is called from a Natural program, this external program must not contain its
own ROLLBACK command if the Natural program issues database calls, too. The
calling Natural program must issue the BACKOUT TRANSACTION
statement for the external program.
The Natural native DML statement DELETE is used to delete a row
from a DB2 table which has been read with a preceding
FIND,
READ, or
SELECT statement.
It corresponds to the SQL statement DELETE WHERE CURRENT OF
cursor-name, which means that only the row
which was read last can be deleted.
Example:
FIND EMPLOYEES WITH NAME = 'SMITH'
AND FIRST_NAME = 'ROGER'
DELETE
Natural would translate the above Natural statements into SQL and
assign a cursor name (for example, CURSOR1) as follows:
DECLARE CURSOR1 CURSOR FOR SELECT FROM EMPLOYEES WHERE NAME = 'SMITH' AND FIRST_NAME = 'ROGER' DELETE FROM EMPLOYEES WHERE CURRENT OF CURSOR1
Both the SELECT and the DELETE statement
refer to the same cursor.
Natural translates a Natural native DML DELETE statement
into a Natural SQL DELETE statement in the same way it translates
a Natural native DML FIND statement into a
Natural SQL SELECT statement.
A row read with a FIND SORTED BY cannot be deleted due to
DB2 restrictions explained with the FIND statement. A row
read with a READ
LOGICAL cannot be deleted either.
The Natural native DML statement END TRANSACTION indicates the
end of a logical transaction and releases all DB2 data locked during the
transaction. All data modifications are committed and made permanent.
How the statement is translated and which command is actually issued depends on the environment:
Under CICS, the END TRANSACTION statement is translated
into an EXEC CICS SYNCPOINT command.
In batch mode, the END
TRANSACTION statement is translated into an SQL COMMIT
WORK command.
As all cursors are closed when a logical unit of work ends, the END TRANSACTION statement must not be placed within a database loop; instead, it has to be placed outside such a loop or after the outermost loop of nested loops.
If an external program written in another standard programming language
is called from a Natural program, this external program must not contain its
own COMMIT command if the Natural program issues
database calls, too. The calling Natural program must issue the END
TRANSACTION statement on behalf of the external program.
Note:
With SQL/DS, the END TRANSACTION statement cannot be
used to store transaction data.
The Natural native DML statement FIND corresponds to the Natural
SQL statement SELECT.
Example:
Natural native DML statements:
FIND EMPLOYEES WITH NAME = 'BLACKMORE' AND AGE EQ 20 THRU 40 OBTAIN PERSONNEL_ID NAME AGE
Equivalent Natural SQL statement:
SELECT PERSONNEL_ID, NAME, AGE
FROM EMPLOYEES
WHERE NAME = 'BLACKMORE'
AND AGE BETWEEN 20 AND 40
Natural internally translates a FIND statement into an SQL
SELECT statement
as described in Processing of SQL Statements Issued
by Natural in the section
Internal Handling of Dynamic
Statements. The SELECT statement is executed
by an OPEN CURSOR statement followed by a
FETCH command. The FETCH
command is executed repeatedly until either all records have been read or the
program flow exits the FIND processing loop. A CLOSE
CURSOR command ends the SELECT processing.
The WITH clause of a
FIND statement is converted to the WHERE clause of
the SELECT statement. The basic search criterion for an SQL/DS
table can be specified in the same way as for an Adabas file. This implies that
only database fields which are defined as descriptors can be used to construct
basic search criteria and that descriptors cannot be compared with other fields
of the Natural view (that is, database fields) but only with program variables
or constants.
Note:
As each database field (column) of a SQL/DS table can be used for
searching, any database field can be defined as a descriptor in a Natural
DDM.
The WHERE clause of the
FIND statement is evaluated by Natural after the rows
have been selected via the WITH clause. Within
the WHERE clause, non-descriptors can be used and database fields
can be compared with other database fields.
Note:
SQL/DS does not have sub-, super-, or phonetic descriptors.
A FIND
NUMBER statement is translated into a SELECT
statement containing a COUNT(*) clause. The number of rows found
is returned in the Natural system variable
*NUMBER
as described in the Natural System Variables
documentation.
The FIND
UNIQUE statement can be used to ensure that only one record
is selected for processing. If the FIND UNIQUE statement is
referenced by an UPDATE statement, a non-cursor (Searched)
UPDATE operation is generated instead of a cursor-oriented
(Positioned) UPDATE operation. Therefore, it can be used if you
want to update an SQL/DS primary key. It is, however, recommended to use the
Natural SQL Searched UPDATE statement to
update a primary key.
In static mode, the FIND NUMBER and FIND
UNIQUE statements are translated into a
SELECT
SINGLE statement as described in the section
Using Natural SQL
Statements.
The FIND
FIRST statement cannot be used. The
PASSWORD,
CIPHER,
COUPLED
and RETAIN
clauses cannot be used either.
The SORTED
BY clause of a FIND statement is translated into
the SQL SELECT ... ORDER BY clause, which follows the search
criterion. Because this produces a read-only result table, a row read with a
FIND statement that contains a SORTED BY clause
cannot be updated or deleted.
A limit on the depth of nested database loops can be specified at installation time. If this limit is exceeded, a Natural error message is returned.
The Natural native DML statement GET is based on Adabas internal
sequence numbers (ISNs) and therefore cannot be used with SQL/DS tables.
The Natural native DML statement HISTOGRAM returns the number
of rows in a table which have the same value in a specific column. The number
of rows is returned in the Natural system variable
*NUMBER
as described in the Natural System Variables
documentation.
Example:
Natural native DML statements:
HISTOGRAM EMPLOYEES FOR AGE OBTAIN AGE
Equivalent Natural SQL statement:
SELECT COUNT(*), AGE FROM EMPLOYEES WHERE AGE > -999 GROUP BY AGE ORDER BY AGE
Natural translates the HISTOGRAM statement into an SQL
SELECT statement, which means that the control flow is similar to
the flow explained for the FIND statement.
The Natural native DML statement READ can also be used to access
SQL/DS tables. Natural translates a READ statement into a Natural
SQL SELECT
statement.
READ
PHYSICAL and READ LOGICAL can be used;
READ BY ISN,
however, cannot be used, as there is no DB2 equivalent to Adabas ISNs. The
PASSWORD
and CIPHER
clauses cannot be used either.
Since a READ LOGICAL statement is translated into a
SELECT ... ORDER
BY statement, which produces a read-only table, a row read
with a READ LOGICAL statement cannot be updated or deleted (see
Example 1). The start value can only be a constant or a program variable; any
other field of the Natural view (that is, any database field) cannot be
used.
A READ PHYSICAL statement is translated into a
SELECT statement without an ORDER BY clause and can
therefore be updated or deleted (see Example 2).
Example 1:
The Natural native DML statements:
READ PERSONNEL BY NAME OBTAIN NAME FIRSTNAME DATEOFBIRTH
Equivalent Natural SQL statement:
SELECT NAME, FIRSTNAME, DATEOFBIRTH FROM PERSONNEL
WHERE NAME >= ' '
ORDER BY NAME
Example 2:
The Natural native DML statements:
READ PERSONNEL PHYSICAL OBTAIN NAME
Equivalent Natural SQL statement:
SELECT NAME FROM PERSONNEL
If the READ statement contains a
WHERE clause,
this clause is evaluated by the Natural processor after the rows have
been selected according to the descriptor value(s) specified in the search
criterion.
The Natural native DML statement STORE is used to add a row to an
SQL/DS table. The STORE statement corresponds to the SQL statement
INSERT.
Example:
The Natural native DML statement:
STORE RECORD IN EMPLOYEES
WITH PERSONNEL_ID = '2112'
NAME = 'LIFESON'
FIRST_NAME = 'ALEX'
Equivalent Natural SQL statement:
INSERT INTO EMPLOYEES (PERSONNEL_ID, NAME, FIRST_NAME)
VALUES ('2112', 'LIFESON', 'ALEX')
The PASSWORD, CIPHER and USING/GIVING
NUMBER clauses of the STORE statement cannot be used.
The Natural native DML statement UPDATE updates a row in an
SQL/DS table which has been read with a preceding
FIND,
READ, or
SELECT statement.
It corresponds to the SQL statement UPDATE WHERE CURRENT OF
cursor-name (Positioned
UPDATE), which means that only the row which was read
last can be updated.
As explained with the Natural native DML statement
FIND, Natural
translates a FIND statement into an SQL
SELECT statement.
When a Natural program contains a DML UPDATE statement, this
statement is translated into an SQL UPDATE statement and a
FOR UPDATE OF clause is
added to the SELECT statement.
Example:
FIND EMPLOYEES WITH SALARY < 5000 ASSIGN SALARY = 6000 UPDATE
Natural would translate the above Natural statements into SQL and assign a cursor name (for example, CURSOR1) as follows:
DECLARE CURSOR1 CURSOR FOR SELECT SALARY FROM EMPLOYEES WHERE SALARY < 5000 FOR UPDATE OF SALARY UPDATE EMPLOYEES SET SALARY = 6000 WHERE CURRENT OF CURSOR1
Both the SELECT and the UPDATE statement
refer to the same cursor.
Due to DB2 logic, a column (field) can only be updated if it is
contained in the FOR UPDATE OF clause; otherwise updating this
column (field) is rejected. Natural includes automatically all columns (fields)
into the FOR UPDATE OF clause which have been modified anywhere in
the Natural program or which are input fields as part of a Natural map.
However, a DB2 column is not updated if the column (field) is marked
as "not updateable" in the Natural DDM. Such columns (fields) are
removed from the FOR UPDATE OF list without any warning or error
message. The columns (fields) contained in the FOR UPDATE OF list
can be checked with the LISTSQL
command.
The Adabas short name in the Natural DDM determines whether a column (field) can be updated.
The following table shows the ranges that apply:
| Short-Name Range | Type of Field |
|---|---|
| AA - N9 | non-key field that can be updated |
| Aa - Nz | non-key field that can be updated |
| OA - O9 | primary key field |
| PA - P9 | ascending key field that can be updated |
| QA - Q9 | descending key field that can be updated |
| RA - X9 | non-key field that cannot be updated |
| Ra - Xz | non-key field that cannot be updated |
| YA - Y9 | ascending key field that cannot be updated |
| ZA - Z9 | descending key field that cannot be updated |
| 1A - 9Z | non-key field that cannot be updated |
| 1a - 9z | non-key field that cannot be updated |
Be aware that a primary key field is never part of a FOR UPDATE
OF list. A primary key field can only be updated by using a non-cursor
UPDATE operation (see also Natural SQL
UPDATE
statement in the section Using Natural SQL Statements).
A row read with a FIND statement that contains a
SORTED
BY clause cannot be updated (due to SQL/DS limitations as
explained with the FIND statement). A row
read with a READ
LOGICAL statement cannot be updated either (as explained with
the READ
statement).
If a column is to be updated which is redefined as an array, it is
strongly recommended to update the whole column and not individual occurrences;
otherwise, results are not predictable. To do so, in reporting mode you can use
the OBTAIN statement,
which must be applied to all field occurrences in the column to be updated. In
structured mode, however, all these occurrences must be defined in the
corresponding Natural view.
The data locked by an UPDATE statement are released when
an END TRANSACTION
(COMMIT WORK) or BACKOUT
TRANSACTION (ROLLBACK WORK) statement is
executed by the program.
Note:
If a length indicator field or NULL indicator field
is updated in a Natural program without updating the field (column) it refers
to, the update of the column is not generated for SQL/DS and thus no updating
takes place.
In general, the Natural native DML statement UPDATE can
be used in both structured and reporting mode. However, after a
SELECT statement, only the syntax defined for Natural structured
mode is allowed:
UPDATE [RECORD] [IN] [STATEMENT] [(r)]
|
This is due to the fact that in combination with the
SELECT statement, the Natural native DML UPDATE
statement is only allowed in the special case of:
... SELECT ... INTO VIEW view-name ...
Thus, only a whole Natural view can be updated; individual columns (fields) cannot.
Example:
DEFINE DATA LOCAL
01 PERS VIEW OF SQL-PERSONNEL
02 NAME
02 AGE
END-DEFINE
SELECT *
INTO VIEW PERS
FROM SQL-PERSONNEL
WHERE NAME LIKE 'S%'
IF NAME = 'SMITH'
ADD 1 TO AGE
UPDATE
END-IF
END-SELECT
...
In combination with the Natural native DML UPDATE
statement, any other form of the SELECT statement is rejected and
an error message is returned.
In all other respects, the Natural native DML UPDATE
statement can be used with the SELECT statement in the same way as
with the Natural FIND statement.
This section covers points you have to consider when using Natural SQL statements with SQL/DS. These SQL/DS-specific points partly consist in syntax enhancements which belong to the Extended Set of Natural SQL syntax. The Extended Set is provided in addition to the Common Set to support database-specific features; see Common Set and Extended Set in the section SQL Statements in the Natural Statements documentation. It also includes features not supported by SQL/DS.
For information on logging SQL statements contained in a Natural program, refer to DBLOG Trace Screen for SQL Statements in the DBLOG Utility documentation.
Below is information on the following Natural SQL statements and on common syntactical items:
The following common syntactical items are either SQL/DS-specific and do not conform to the standard SQL syntax definitions (that is, to the Common Set of Natural SQL syntax) or impose restrictions when used with SQL/DS (see also SQL Statements in the Natural Statements documentation).
Below is information on the following common syntactical items:
An atom can be either a parameter (that is, a Natural program variable or host variable) or a constant. When running dynamically, however, the use of host variables is restricted by SQL/DS. For further details, refer to the relevant SQL/DS literature by IBM.
The comparison operators specific to SQL/DS belong to the Natural Extended Set. For a description, refer to Comparison Predicate in Search Condition, Natural SQL Statements in the Natural Statements documentation.
The following factors are specific to SQL/DS and belong to the Natural SQL Extended Set:
|
special-register |
A scalar function is a built-in function that can be used in the construction of scalar computational expressions. Scalar functions are specific to SQL/DS and belong to the Natural SQL Extended Set.
The following scalar functions are supported:
CHAR
DATE
DAY
DAYS
DECIMAL
DIGITS
FLOAT
HEX
HOUR
INTEGER
LENGTH
MICROSECOND
MINUTE
MONTH
SECOND
STRIP
SUBSTR
TIME
TIMESTAMP
TRANSLATE
VALUE
VARGRAPHIC
YEAR
Each scalar function is followed by one or more scalar expressions in parentheses. The number of scalar expressions depends upon the scalar function. Multiple scalar expressions must be separated from one another by commas.
Example:
SELECT NAME
INTO NAME
FROM SQL-PERSONNEL
WHERE SUBSTR ( NAME, 1, 3 ) = 'Fri'
...
The concatenation operator (CONCAT or ||)
does not conform to standard SQL. It is specific to SQL/DS and belongs to the
Natural Extended Set.
The following special registers do not conform to standard SQL. They are specific to SQL/DS and belong to the Natural SQL Extended Set:
USER
CURRENT TIMEZONE
CURRENT DATE
CURRENT TIME
CURRENT TIMESTAMP
A reference to a special register returns a scalar value.
Units, also called "durations", are specific to SQL/DS and belong to the Natural SQL Extended Set.
The following units are supported:
DAY
DAYS
HOUR
HOURS
MICROSECOND
MICROSECONDS
MINUTE
MINUTES
MONTH
MONTHS
SECOND
SECONDS
YEAR
YEARS
The Natural SQL statement COMMIT indicates the end of a
logical transaction and releases all SQL/DS data locked during the transaction.
All data modifications are made permanent.
COMMIT is a synonym for the Natural native DML statement
END
TRANSACTION as described in the section
Using Natural Native DML
Statements.
As all cursors are closed when a logical unit of work ends, the
COMMIT statement must not be placed within a database loop;
instead, it has to be placed outside such a loop or after the outermost loop of
nested loops.
If an external program written in another standard programming language
is called from a Natural program, this external program must not contain its
own COMMIT command if the Natural program issues database calls,
too. The calling Natural program must issue the COMMIT statement
on behalf of the external program.
For further details and statement syntax, see COMMIT - SQL in the Natural Statements documentation.
Both the cursor-oriented or
Positioned
DELETE, and the non-cursor or
Searched
DELETE statements are supported as part of Natural SQL;
the functionality of the Positioned DELETE statement corresponds
to that of the Natural native DML DELETE statement.
With SQL/DS, a table name in the
FROM
clause of a Searched
DELETE statement can be assigned a correlation-name.
This does not correspond to the standard SQL syntax definition and therefore
belongs to the Natural SQL Extended
Set.
For further details and statement syntax, see DELETE - SQL in the Natural Statements documentation.
The Natural SQL statement INSERT is used to add one or
more new rows to a table.
Since the SQL INSERT statement can contain a select
expression, all the SQL/DS-specific common syntactical items described
above apply.
For further details and statement syntax, see INSERT - SQL in the Natural Statements documentation.
The Natural SQL statement PROCESS SQL is used to issue SQL
statements to the underlying database. The statements are specified in a
statement-string, which can also
include constants and parameters. The set of statements which can be issued is
also referred to as Flexible SQL and comprises those statements which can be
issued with the SQL statement EXECUTE.
In addition, Flexible SQL includes the following SQL/DS-specific
statement CONNECT.
With the PROCESS SQL statement you can also specify the
statement-string
SQLDISCONNECT to release the connection to your SQL/DS application
server. SQLDISCONNECT is transformed into the SQL/DS
ROLLBACK WORK RELEASE command.
Execution of SQLDISCONNECT is only allowed if no
transaction (logical unit of work) is open. Therefore, an explicit
COMMIT (END TRANSACTION) or ROLLBACK
(BACKOUT TRANSACTION) statement is required before executing
SQLDISCONNECT, otherwise an error message is returned.
Note:
To avoid transaction synchronization problems between the Natural
environment and SQL/DS, the COMMIT and
ROLLBACK statements must not be used within PROCESS
SQL.
For further details and statement syntax, see PROCESS SQL in the Natural Statements documentation.
The Natural SQL statement ROLLBACK undoes all
database modifications made since the beginning of the last logical
transaction. Logical transactions can start either after the beginning of a
session or after the last COMMIT/END TRANSACTION or
ROLLBACK/BACKOUT TRANSACTION statement. All records
held during the transaction are released.
ROLLBACK is a synonym for the Natural statement
BACKOUT
TRANSACTION as described in the section
Using Natural Native DML
Statements.
As all cursors are closed when a logical unit of work ends, a
ROLLBACK statement must not be placed within a database loop;
instead, it has to be placed outside such a loop or after the outermost loop of
nested loops.
If an external program written in another standard programming language
is called from a Natural program, this external program must not contain its
own ROLLBACK command if the Natural program issues database calls,
too. The calling Natural program must issue the ROLLBACK statement
on behalf of the external program.
For further details and statement syntax, see ROLLBACK -SQL in the Natural Statements documentation.
The Natural SQL SELECT statement supports both the
cursor-oriented selection, which is used to retrieve an arbitrary number of rows,
and the non-cursor selection (Singleton SELECT), which retrieves at
most one single row.
Like the Natural native DML FIND statement, the cursor-oriented
SELECT statement is used to select a set of rows (records) from
one or more SQL/DS tables, based on a search criterion. Since a database loop is
initiated, the loop must be closed by a LOOP statement (in reporting mode) or
by an END-SELECT statement (in structured mode). With this construction, Natural uses the
same loop processing as with the FIND statement. In addition, no
cursor management is required from the application program; it is automatically
handled by Natural.
For further details and syntax, see SELECT SQL, Syntax 1 - Cursor-Oriented Selection in the Natural Statements documentation.
The Natural SQL statement SELECT SINGLE provides the
functionality of a non-cursor selection (Singleton SELECT); that
is, a select expression that retrieves at most one row without using a
cursor.
Since SQL/DS supports the Singleton SELECT command in static
SQL only, in dynamic mode, the Natural SELECT SINGLE statement is
executed like a set-level SELECT statement, which results in a
cursor operation. However, Natural checks the number of rows returned by SQL/DS.
If more than one row is selected, a corresponding error message is
returned.
For further details and syntax, see SELECT SQL, Syntax 2 - Non-Cursor Selection in the Natural Statements documentation.
Both the cursor-oriented or Positioned UPDATE and the
non-cursor or Searched UPDATE statements are supported as part of
Natural SQL. Both of them reference either a table or a Natural view.
With SQL/DS, the name of a table or Natural view to be referenced by a
Searched UPDATE can be assigned a
correlation-name. This does not correspond to the
standard SQL syntax definition and therefore belongs to the Natural
Extended Set.
The Searched UPDATE statement must be used, for example,
to update a primary key field, since SQL/DS does not allow updating of columns
of a primary key by using a Positioned UPDATE statement.
Note:
If you use the SET * notation, all fields of the
referenced Natural view are added to the FOR UPDATE OF and
SET lists. Therefore, ensure that your view contains only fields
which can be updated; otherwise, a negative SQLCODE is returned by
SQL/DS.
For further details and syntax, see UPDATE - SQL in the Natural Statements documentation.
When used with DB2, there are restrictions and/or special considerations concerning the following Natural system variables:
For information on restrictions and/or special considerations, refer to the section Database-Specific Information in the corresponding system variable documentation.
In contrast to the normal Natural error handling, where either an
ON ERROR statement is
used to intercept execution time errors or standard error message processing is
performed and program execution is terminated, the enhanced error handling of
Natural for DB2 provides an application controlled reaction to the encountered
SQL error.
Two Natural subprograms, NDBERR and
NDBNOERR, are
provided to disable the usual Natural error handling and to check the
encountered SQL error for the returned SQL code. This functionality replaces
the E function of the DB2SERV interface, which is
still provided but no longer documented.
For further information on Natural subprograms provided for SQL/DS, see the section Interface Subprograms.
Example:
DEFINE DATA LOCAL
01 #SQLCODE (I4)
01 #SQLSTATE (A5)
01 #SQLCA (A136)
01 #DBMS (B1)
END-DEFINE
*
* Ignore error from next statement
*
CALLNAT 'NDBNOERR'
*
* This SQL statement produces an SQL error
*
INSERT INTO SYSIBH-SYSTABLES (CREATOR, NAME, COLCOUNT)
VALUES ('SAG', 'MYTABLE', '3')
*
* Investigate error
*
CALLNAT 'NDBERR' #SQLCODE #SQLSTATE #SQLCA #DBMS
*
IF #DBMS NE 2 /* not DB2
MOVE 3700 TO *ERROR-NR
END-IF
*
DECIDE ON FIRST VALUE OF #SQLCODE
VALUE 0, 100 /* successful execution
IGNORE
VALUE -803 /* duplicate row
/* UPDATE existing record
/*
IGNORE
NONE VALUE
MOVE 3700 TO *ERROR-NR
END-DECIDE
*
END