This section covers the following topics:
To enable Natural to access a DB2 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 DB2 tables. This function is invoked from the main menu of SYSDDM and is described on the following pages.
The SQL Services function of the Natural SYSDDM utility (see the relevant documentation) is used to access DB2 tables. You access the catalog of the DB2 server to which you are connected, for example, by using the Environment Setting function as described in Natural Tools for DB2, or by entering the name of a server in the Server Name field on the SQL Services Menu. The name of the DB2 server to which you are connected is then displayed in the top left-hand corner of the screen SQL Services Menu. You can access any DB2 server that is located on either a mainframe (z/OS or z/VSE) or a UNIX platform if the servers have been connected via DRDA (Distributed Relational Database Architecture). For further details on connecting DB2 servers and for information on binding the application package (SYSDDM uses I/O module NDBIOMO) to access data on remote servers, refer to the relevant IBM literature.
The SQL Services function determines whether you are connected to a mainframe DB2 (z/OS or z/VSE) or a UNIX DB2, access the appropriate DB2 catalog and performs the functions listed below.
If you use SYSDDM SQL services in a CICS environment without file server, specify CONVERS=ON in the NDBPARM module (see the relevant section in Installing Natural for DB2); otherwise you might get SQL code -518.
If you select SQL Services 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 DB2 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 to the DB2 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 Creator 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 DB2 tables requested.
On the list, you can mark a DB2 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 a DB2 table, based on the definitions in the DB2 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/creator, you can use the function Select SQL Table from a List to choose the table you want.
If you do not want the creator 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 DB2 must be avoided. DB2 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 DB2 tables is specified in the NTDB 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).
After a valid DBID and FNR have been assigned, a DDM is automatically generated from the specified table.
The maximum field length supported by Natural is 1 GB-1 (1073741823 bytes). If a DB2 table contains a column which is longer than 253 bytes or if a DB2 column is defined as a DB2 LOB field, the pop-up window Long Field Generation will be invoked automatically. A DB2 LOB field may be defined as a simple Natural variable with a maximum length of 1GB-1, or as a dynamic Natural variable.
A field which is longer than 253 bytes and which is not a DB2 LOB field may be defined as a simple Natural field with a maximum length of 1GB-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 Statements and System Variables), care must be taken to
update each occurrence appropriately.
For each of the columns listed above, an additional length indicator field (format/length I2 or I4 for LOB fields) 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, LONG VARGRAPHIC or DBCLOB 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 a DB2 column.
When a Natural DDM is generated from the DB2 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 a DB2 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.
For each LOB column, an additional locator field will be generated in the I4 format.
A LOB locator may be used to reference a LOB value in the DB2 database server, when a LOB value is not needed locally in a program.
This function lists all columns of a specific DB2 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 DB2 name of the column. | ||||
| Type | The column type. | ||||
| Length | The length (or precision if Type is DECIMAL) of the column as defined in the DB2 catalog. | ||||
| Scale | The decimal scale of the column (only applicable if Type is DECIMAL). | ||||
| Update |
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| Nulls |
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| 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. |
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.
For DB2, Natural provides a DB2 TIMESTAMP column as an alphanumeric field (A26) in the format YYYY-MM-DD-HH.SS.MMMMMM.
