This section covers the following topics:
To enable Natural to access an SQL table, a logical Natural data
definition module (DDM) of the table must be generated. This is done either
with Predict (see the relevant Predict documentation for details) or with the
Natural utility SYSDDM.
If you do not have Predict installed, use the SYSDDM
function SQL Services to generate Natural DDMs from SQL
tables. This function is invoked from the main menu of SYSDDM and
is described on the following pages.
The SQL Services (NSB) function of the Natural
SYSDDM utility (see the relevant documentation) is used to access
SQL tables. You access the CXX CDD (ConnecX data dictionary) of your current
CXX connection to retrieve table definitions for Natural DDM generation.
The name of the CDD catalog you access is displayed in the top left-hand corner of the screen SQL Services Menu. You can access any catalog contained in the CDD. For further details on the CDD structure read the ConnecX documentation.
If you select SQL Services (NSB) on the main menu of the
SYSDDM utility, a menu is displayed, which offers you the
following functions:
This function is used to select a catalog from the catalogs defined in the CDD for further processing.
To invoke this function, enter function code C on the SQL
Services Menu.
If you enter the function only, you obtain a list of all catalogs defined in the current CDD.
On the list, you can mark an SQL catalog with S to select a catalog for further processing.
The selected catalog is displayed in the left corner of the second header line of following maps and in the Catalog name field of the SQL Services Menu, where the catalog name could also be entered. If you did not explicitly specify a catalog name it is set to either the current default catalog of the CXX connection – if it is not equal spaces- or the first catalog found in the current CDD.
This function is used to verify the actual CXX connection. It displays the current parameters of the actual connection. These parameters are:
| Parameter | Description |
|---|---|
GATEWAY
|
Specifies the IP-address of the CXX server connected to. |
DD
|
Specifies the registered data source name of the CDD in use. |
PORT
|
Specifies the port number the CXX server is listening to. |
User
|
Specifies the user name of the CXX connection. |
Password
|
Specifies the password used for the CXX connection(invisible). |
Catalog
|
Specifies the current default catalog name of the CXX connection. |
Schema
|
Specifies the current default schema name of the CXX connection. |
Version
|
Displays the RCI version string of the CXX connection. |
State
|
Displays the CXX connection state. |
To invoke this function, enter function code X on the
SQL Services Menu.
The parameters of the connection could be changed and the connection could be (re-)established with the entered parameters by pressing PF5 (Update).
This function is used to select an SQL table from a list for further processing.
To invoke the function, enter function code S on the
SQL Services Menu.
If you enter the function code only, you obtain a list of all tables defined in the selected SQL catalog.
If you do not want a list of all tables but would like only a certain
range of tables to be listed, you can, in addition to the function code,
specify a start value in the Table Name and/or Schema
fields. You can also use asterisk notation (*) for the start value.
When you invoke the function, the Select SQL Table from a List screen is invoked displaying a list of all SQL tables requested.
On the list, you can mark an SQL table with either G for
Generate DDM from an SQL table or L for
List Columns of an SQL table. Then the corresponding
function is invoked for the marked table.
This function is used to generate a Natural DDM from an SQL table, based on the definitions in the SQL catalog.
To invoke the function, enter function code G on the
SQL Services Menu along with the name and creator of the
table for which you wish a DDM to be generated.
If you do not know the table name/schema, you can use the function Select SQL Table from a list to choose the table you want.
If you do not want the schema name of the table to be part of the DDM
name, enter an N in the field DDM Name with Creator
when you invoke the Generate function (default is
Y).
Important:
Since the specification of any special characters as part of a
field or DDM name does not comply with Natural naming conventions, any special
characters allowed within SQL must be avoided. SQL delimited identifiers must
be avoided, too.
If you wish to generate a DDM for a table for which a DDM already
exists and you want the existing one to be replaced by the newly generated one,
enter a Y in the Replace field when you invoke the
Generate function.
By default, Replace is set to N to prevent an
existing DDM from being replaced accidentally. If Replace is
N, you cannot generate another DDM for a table for which a DDM has
already been generated.
When the function Generate DDM from an SQL Table is invoked for a table for which a DDM is to be generated for the first time, the DBID/FNR Assignment screen is displayed. If a DDM is to be generated for a table for which a DDM already exists, the existing DBID and FNR are used and the DBID/FNR Assignment screen is suppressed.
On the DBID/FNR Assignment screen, enter one of the database IDs (DBIDs) chosen at Natural installation time, and the file number (FNR) to be assigned to the DB2 table. Natural requires these specifications for identification purposes only.
The range of DBIDs which is reserved for SQL tables is specified in the
NTDB
parameter macro of the Natural parameter module (see the Natural
Parameter Reference documentation) in combination with the
NDBID macro of the parameter module
NDBPARM. Any DBID not within this range is not accepted. The FNR
can be any valid file number within the database (between 1 and 255).
The maximum field length supported by CXX is 32 KB - 1. If an SQL table contains a column which is longer than 253 bytes, the pop-up window Long Field Generation will appear automatically.
A field which is longer than 253 bytes may be defined as a simple Natural field with a maximum length of 32 KB -1, or as an array. In the DDM, such an array is represented as a multiple-value variable.
If, for example, a DB2 column has a length of 2000 bytes, you can specify an array element length of 200 bytes, and you receive a multiple-value field with 10 occurrences, each occurrence with a length of 200 bytes.
Since redefined long fields are not multiple-value fields in the sense of Natural, the Natural C* notation makes no sense here and is therefore not supported.
When such a redefined long field is defined in a Natural view to be referenced by Natural SQL statements (that is, by host variables which represent multiple-value fields), both when defined and when referenced, the specified range of occurrences (index range) must always start with occurrence 1. If not, a Natural syntax error is returned.
UPDATE table SET varchar = #arr(*) SELECT ... INTO #arr(1:5)
Note:
When such a redefined long field is updated with the Natural DML
UPDATE statement (see
the relevant section in the Statements documentation),
care must be taken to update each occurrence appropriately.
For each of the columns listed above, an additional length indicator
field (format/length I2) is generated in the DDM. The length is always measured
in number of characters, not in bytes. To obtain the number of bytes of a
VARGRAPHIC or LONG VARGRAPHIC field, the length must
be multiplied by 2.
The name of a length indicator field begins with L@
followed by the name of the corresponding field. The value of the length
indicator field can be checked or updated by a Natural program.
If the length indicator field is not part of the Natural view and if
the corresponding field is a redefined long field, the length of this field
with UPDATE and STORE operations is calculated
without trailing blanks.
With Natural, it is possible to distinguish between a null value and the actual value zero (0) or blank in an SQL column.
When a Natural DDM is generated from the SQL catalog, an additional
NULL indicator field is generated for each column which can be
NULL; that is, which has neither NOT NULL nor
NOT NULL WITH DEFAULT specified.
The name of the NULL indicator field begins with
N@ followed by the name of the corresponding field.
When the column is read from the database, the corresponding indicator field contains either zero (0) (if the column contains a value, including the value 0 or blank) or -1 (if the column contains no value).
The column NULLCOL CHAR(6) in an SQL table definition
would result in the following view fields:
NULLCOL A 6.0 N@NULLCOL I 2.0
When the field NULLCOL is read from the database, the
additional field N@NULLCOL contains:
0 (zero) if NULLCOL contains a value (including the
value 0 or blank),
-1 (minus one) if NULLCOL contains no value.
A null value can be stored in a database field by entering -1 as input
for the corresponding NULL indicator field.
Note:
If a column is NULL, an implicit RESET is
performed on the corresponding Natural field.
This function lists all columns of a specific SQL table.
To invoke this function, enter Function Code L on the
SQL Services Menu along with the name and creator of the
table whose columns you wish to be listed.
The List Columns screen for this table is invoked, which lists all columns of the specified table and displays the following information for each column:
| Variable |
Content |
|---|---|
Name
|
The name of the column. |
Type
|
The column type. |
Length
|
The length (or precision if |
Scale
|
The decimal scale of the column (only applicable if
|
Update
|
|
Nulls
|
|
Not
|
A column which is of a scale length or type not supported by Natural is marked with an asterisk (*). For such a column, a view field cannot be generated. The maximum scale length supported is 7 bytes. Types supported are:
|
The data types DATE, TIME,
TIMESTAMP, FLOAT and ROWID are converted
into numeric or alphanumeric fields of various lengths: DATE is
converted into A10, TIME into A8, TIMESTAMP into A26,
FLOAT into F8 and ROWID into A40.
When you invoke the function, the Select SQL Table from a List screen is invoked displaying a list of all SQL tables requested.
For SQL, Natural provides an SQL TIMESTAMP column as an
alphanumeric field (A26) in the format
YYYY-MM-DD-HH.SS.MMMMMM.
Since Natural does not yet support computations with such fields, a
Natural subprogram called NDBSTMP is provided to enable this kind
of functionality.
