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.
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:
Natural SQL Gateway supports the following special registers, which can
be set via the PROCESS
SQL statement:
SCHEMA
The SCHEMA special register determines the implicitly first
level qualifier of table names, that is, the schema or creator name of the
table, if the first qualifier is not explicitly specified. The
SCHEMA special register could be set by PROCESS SQL
ddm-name << SET SCHEMA =
:hv>>, where
ddm-name denotes the DDM whose DBID is
mapped to type CNX and :hv denotes an
alphanumeric variable containing the first level qualifier.
The SCHEMA special register cannot be retrieved or
interrogated by SQL statements.
CATALOG
The CATALOG special register determines the implicitly
second level qualifer of table names, that is, the location or database name of
the table, if the second level qualifier is not explicitly specified. The
CATALOG special register could be set by PROCESS SQL
ddm-name << SET CATALOG =
:hv>>, where
ddm-name denotes DDM whose DBID is
mapped to type CNX and :hv
denotes a alphanumeric variable containing the second level qualifier.
The CATALOG special register could not be retrieved or
interrogated by SQL statements.
RCI_VERSION
The RCI_VERSION is an alphanumeric character string
containing the version of the remote client interface used to communicate with
the CONNX JDBC server. The RCI_VERSION is a read-only special
register which could be retrieved by PROCESS SQL ddm-name
<<GET :hv = RCI_VERSION>>, where
ddm-name denotes a DDM whose DBID is
mapped to type CNX and :hv denotes a alphanumeric
variable. The RCI_VERSION string has the following format:
RCI: 4.1.1 CONNX 10.5 SP2 (build 7294)
This section summarizes particular points you have to consider when using Natural DML statements with SQL. Any Natural statement not mentioned in this section can be used with SQL without restriction.
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 TP-monitor environment:
In batch mode and under TSO, the BACKOUT TRANSACTION statement
is translated into an SQL ROLLBACK command.
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.
If a program tries to backout updates which have already been committed, for example by a terminal I/O, a corresponding Natural error message (NAT3711) is returned.
The Natural native DML statement DELETE is used to delete a row
from an SQL 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 DML DELETE statement into an SQL
DELETE statement in the same way it translates a FIND
statement into an SQL SELECT statement.
A row read with a FIND SORTED BY cannot be deleted due to
SQL restrictions explained with the FIND statement. A row read
with a READ LOGICAL cannot be deleted either.
If a row rolled out to the file server is to be deleted, Natural
rereads automatically the original row from the database to compare it with its
image stored in the file server. If the original row has not been modified in
the meantime, the DELETE operation is performed. With the next
terminal I/O, the transaction is terminated, and the row is deleted from the
actual database.
If the DELETE operates on a scrollable cursor, the row on
the file server is marked as DELETE hole and is deleted from the
base table.
However, if any modification is detected, the row will not be deleted and Natural issues the NAT3703 error message for non-scrollable cursors.
Since a DELETE statement requires that Natural rereads a
single row, a unique index must be available for the respective table. All
columns which comprise the unique index must be part of the corresponding
Natural view.
The Natural native DML statement END TRANSACTION indicates the
end of a logical transaction and releases all SQL 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 TP-monitor environment:
In batch mode and under TSO, the END TRANSACTION statement is
translated into an SQL COMMIT WORK command.
An END TRANSACTION statement must not be placed within a
database loop, since all cursors are closed when a logical unit of work ends.
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 for the external program.
Note:
Transaction data cannot be written to SQL databases.
The Natural native DML statement FIND corresponds to the SQL
SELECT statement.
Example:
Natural statements:
FIND EMPLOYEES WITH NAME = 'BLACKMORE' AND AGE EQ 20 THRU 40 OBTAIN PERSONNEL_ID NAME AGE
Equivalent SQL statements:
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 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 an SQL 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 tables do 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 primary key. It is, however, recommended
to use 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 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.
As far as the file server is concerned, there are no programming restrictions with selection statements. It is, however, recommended to make yourself familiar with its functionality considering performance and file server space requirements.
The Natural native DML statement GET is based on Adabas internal
sequence numbers (ISNs) and therefore cannot be used with SQL tables.
The Natural 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 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 DML statement READ can also be used to access
SQL tables. Natural translates a READ statement into an SQL
SELECT statement.
READ PHYSICAL and READ LOGICAL can be used;
READ BY ISN, however, cannot be used, as there is no SQL
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 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:
Natural native DML statements:
READ PERSONNEL BY NAME OBTAIN NAME FIRSTNAME DATEOFBIRTH |
Equivalent Natural SQL statements:
SELECT NAME, FIRSTNAME, DATEOFBIRTH FROM PERSONNEL
WHERE NAME >= ' '
ORDER BY NAME |
Example 2:
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.
As far as the file server is concerned there are no programming restrictions with selection statements. It is, however, recommended to make yourself familiar with its functionality considering performance and file server space requirements.
The Natural DML statement STORE is used to add a row to an
SQL table. The STORE statement corresponds to the SQL statement
INSERT.
Example:
Natural native DML statements:
STORE RECORD IN EMPLOYEES
WITH PERSONNEL_ID = '2112'
NAME = 'LIFESON'
FIRST_NAME = 'ALEX' |
Equivalent Natural SQL statements:
INSERT INTO EMPLOYEES (PERSONNEL_ID, NAME, FIRST_NAME)
VALUES ('2112', 'LIFESON', 'ALEX') |
The PASSWORD, CIPHER and
USING/GIVING NUMBER clauses cannot be used.
The Natural DML UPDATE statement updates a
row in an SQL 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.
If a row rolled out to the file server is to be updated, Natural
automatically rereads the original row from the database to compare it with its
image stored in the file server. If the original row has not been modified in
the meantime, the UPDATE operation is performed. With the next
terminal I/O, the transaction is terminated and the row is definitely updated
on the database.
If the UPDATE operates on a scrollable cursor, the row on
the file server and the row in the base table are updated. If the row no longer
qualifies for the search criteria of the related SELECT statement
after the update, the row is marked as UPDATE hole on the file
server.
However, if any modification is detected, the row will not be updated and Natural issues the NAT3703 error message.
Since an UPDATE statement requires rereading a single row
by Natural, a unique index must be available for this table. All columns which
comprise the unique index must be part of the corresponding Natural view.
As explained with the FIND statement, Natural translates a
FIND statement into an SQL SELECT statement. When a
Natural program contains a Natural native 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 SQL 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, an SQL 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 UPDATE in the section
Natural SQL Statements).
A row read with a FIND statement that contains a
SORTED BY clause cannot be updated (due to SQL limitations as
explained with the FIND statement). A row read with a READ
LOGICAL 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 (as described in the Natural Statements
documentation), 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 and thus no updating takes
place.
In general, the DML UPDATE statement 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 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.
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 described earlier in this section
and in the Natural
Statements documentation.
This section covers points you have to consider when using Natural SQL statements with Natural SQL Gateway. These SQL specific points mainly consists in syntax restrictions or 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.
This section covers the following topics:
The following common syntactical items are either Natural SQL Gateway (NSB) 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 Natural SQL Gateway (see also SQL Statements in the Natural Statements documentation).
This section covers the following topics:
An atom can be either a parameter (that is, a Natural program variable or host variable) or a constant.
The following factors are specific to Natural SQL Gateway and belong to the Natural 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 Natural SQL Gateway and belong to the Natural Extended Set.
See the CONNX Users Guide for available scalar functions.
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'
...
A column function returns a single-value result for the argument it receives. The argument is a set of like values, such as the values of a column. Column functions are also called aggregating functions.
The following column functions conform to standard SQL.
AVG COUNT MAX MIN SUM
The concatenation operator (CONCAT or "||")
does not conform to standard SQL and belongs to the
Extended Set.
The following special registers do not conform to standard SQL and belong to the Extended Set:
USER
A reference to a special register returns a scalar value.
CASE
|
|
searched-when-clause ...
|
|
|
ELSE
|
|
|
|
|
END
|
case-expressions do not
conform to standard SQL and are therefore supported by the Natural SQL
Extended Set only.
Example:
DEFINE DATA LOCAL
01 #EMP
02 #EMPNO (A10)
02 #FIRSTNME (A15)
02 #MIDINIT (A5)
02 #LASTNAME (A15)
02 #EDLEVEL (A13)
02 #INCOME (P7)
END-DEFINE
SELECT EMPNO, FIRSTNME, MIDINIT, LASTNAME,
(CASE WHEN EDLEVEL < 15 THEN 'SECONDARY'
WHEN EDLEVEL < 19 THEN 'COLLEGE'
ELSE 'POST GRADUATE'
END ) AS EDUCATION, SALARY + COMM AS INCOME
INTO
#EMPNO, #FIRSTNME, #MIDINIT, #LASTNAME,
#EDLEVEL, #INCOME
FROM DSN8510-EMP
WHERE (CASE WHEN SALARY = 0 THEN NULL
ELSE SALARY / COMM
END ) > 0.25
DISPLAY #EMP
END-SELECT
END
The Natural SQL COMMIT statement indicates the end of a
logical transaction and releases all SQL 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 DML Statements.
No transaction data can be provided with the COMMIT
statement.
If the file server is used, an implicit end-of-transaction is issued after each terminal I/O.
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 for 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 SQL statements are supported as part
of Natural SQL Gateway; the functionality of the positioned DELETE
statement corresponds to that of the Natural DML DELETE statement.
With Natural SQL Gateway, 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 Extended Set.
The searched DELETE statement must be used, for example,
to delete a row from a self-referencing table, since with self-referencing
tables a positioned DELETE is not allowed by Natural SQL Gateway.
For further details and statement syntax, see DELETE - SQL in the Natural Statements documentation.
The Natural SQL INSERT statement is used to add one or
more new rows to a table.
Since the INSERT statement can contain a select
expression, all the syntactical items described in the section Syntactical Items Common to Natural SQL Statements apply.
For further details and statement syntax, see INSERT - SQL in the Natural Statements documentation.
The Natural PROCESS
SQL statement 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 Natural SQL Gateway specific statements:
CONNECT
SET
CATALOG
SET
SCHEMA
GET
host-variable =
RCI_VERSION
For further details and statement syntax, see PROCESS SQL in the Natural Statements documentation.
The CONNECT statement establishes a connection to the
CONNX JDBC server. It has to be executed before any SQL statement is issued
against the CONNX JDBC server.
PROCESS SQL ddm << CONNECT TO :U:server USER :U:user PASSWORD :U:password >>
| Parameter | Format/Length | Explanation |
|---|---|---|
ddm |
Constant 1-32 characters | Specifies the name of a DDM whose DBID is mapped by
NTDBID to type SQL and mapped by
NTDBID to type CNX.
|
server
|
A1 to A128 | Specifies a string addressing the CONNX JDBC server , the port
number the server listens to and the CDD to be used to access the RDBMS.
The string has to have the following format: GATEWAY=location-name;PORT=number;DD=cdd-registered-name
Default port number is 7500.
|
user
|
A1 to A32 | Denotes the user ID to logon to the CONNX JDBC server or RDBMS. |
password
|
A1 to A32 | Denotes the password to logon to the CONNX JDBC server or RDBMS. |
PROCESS SQL ddm << SET CATALOG :U:catalog >>
The SET CATALOG statement sets the default catalog to the
catalog identified by catalog. The default catalog will be used to identify the
database system to be accessed, if the database system is not explicitly
specified as first qualifier of a table name in the SQL syntax and if the CDD
contains definitions of more than one database system.
| Parameter | Format/Length | Explanation |
|---|---|---|
ddm |
Constant 1-32 characters | Specifies the name of a DDM whose DBID is mapped by
NTDBID to type SQL and mapped by
NTDBID to type CNX.
|
catalog |
A1 to A32 | Denotes the catalog name to be used as default catalog. |
PROCESS SQL ddm << SET SCHEMA :U:schema >>
The SET SCHEMA statement sets the default schema to the
schema identified by schema. The default schema will be used to identify the
schema to be accessed, if the schema is not explicitly specified as qualifier
of a table name in the SQL syntax and if the CDD contains definitions of more
than one schema.
| Parameter | Format/Length | Explanation |
|---|---|---|
ddm |
Constant 1-32 characters | Specifies the name of a DDM whose DBID is mapped by
NTDBID to type SQL and mapped by
NTDBID to type CNX.
|
schema |
A1 to A32 | Denotes the schema name to be used as default schema. |
PROCESS SQL ddm << GET:G:version = RCI_VERSION >>
The GET RCI_VERSION statement retrieves the version of
the CONNX client software used in the actual session. It could be executed
before any connection is established.
| Parameter | Format/Length | Explanation |
|---|---|---|
ddm |
Constant 1-32 characters | Specifies the name of a DDM whose DBID is mapped by
NTDBID to type SQL and mapped by
NTDBID to type CNX.
|
version |
A1 to A128 | Receives the version string of the CONNX client software. It
looks like the following: RCI: 4.1.1 CONNX 10.5 SP3 (build
8003).
|
To avoid transaction synchronization problems between the Natural
environment and SQL, 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 ROLLBACK statement 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 DML Statements.
However, if the file server is used, only changes made to the database since the last terminal I/O are undone.
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 for 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.
For further details and statement syntax, see SELECT - SQL in the Natural Statements documentation.
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 tables, based on a search criterion. Since a database loop is
initiated, the loop must be closed by a LOOP (in reporting mode)
or 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 supports the Singleton SELECT
command in static SQL only, in dynamic mode, the Natural SELECT
SINGLE statement is executed in the same way as a set-level
SELECT statement, which results in a cursor operation. However,
Natural checks the number of rows returned by SQL. 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 SQL statements are supported as part
of Natural SQL. Both of them reference either a table or a Natural view.
With SQL, 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 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.
For further details and syntax, see UPDATE - SQL in the Natural Statements documentation.
When used with SQL, 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 SQL Gateway 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.
For further information on Natural subprograms provided for SQL, see the section Interface Subprograms.