Cursors

Dynamic SQL

Chapter 5: Data Structures

The Net Express SQL preprocessors use two data structures:

Data Structure	Description	Function
SQLCA	SQL Communications Area	Returns status and error information.
SQLDA	SQL Descriptor Area	Describes the variables used in dynamic SQL statements.

5.1 SQL Communications Area (SQLCA)

After each embedded SQL statement is executed, error and status information is returned in the SQL Communications Area (SQLCA).

Full details of the layout of the SQLCA data structure are given in the online help file. Look under SQLCA in the help file index.

The SQLCA contains two variables (sqlcode and sqlstate) plus a number of warning flags which are used to indicate whether an error has occurred in the most recently executed SQL statement.

COBSQL
For COBSQL, SQLSTATE is a separate data item. For the currently supported versions of Oracle and Sybase, the SQLCA should be used in preference to the SQLSTATE variable. The SQLSTATE variable will eventually supersede the SQLCA as the preferred method of passing data between the database and the client application, but this is not yet the case.

5.1.1 The SQLCODE Variable

Testing the value of sqlcode is the most common way of determining the success or failure of an embedded SQL statement. The possible values for sqlcode are:

Value	Meaning
0	The statement ran without error.
1	The statement ran, but a warning was generated. The values of the `sqlwarn` flags should be checked to determine the type of error.
100	Data matching the query was not found or the end of the results set has been reached. No rows were processed.
< 0 (negative)	The statement did not run due to an application, database, system, or network error.

Full details of SQLCODE values are given in the online help file. Look under "SQLCODE" in the help file index.

COBSQL and DB2
For COBSQL and DB2, it is possible to get other positive values. This means that the SQL statement has executed but produced a warning.

COBSQL

For details about the range of positive values that SQLCODE can be set to, consult your Oracle, Sybase or Informix Error Messages manual. The above SQLCODES are produced by OpenESQL. The values for SQLCODE and the errors reported by Oracle, Sybase and Informix are all different. Please refer to Oracle, Sybase or Informix Error Messages manuals for more information on the errors returned.
The value +100 is the ANSI standard for 'data not found'. Oracle can return another value for 'data not found'. To get Oracle to return the value +100 for 'data not found', either of the Oracle precompiler directives MODE=ANSI or END_OF_FETCH=100 must be set. This will affect other aspects of the way the Oracle precompiler handles SQL statements. For more details on the Oracle precompiler MODE or END_OF_FETCH=+100 directives, refer to the Programmer's Guide to the ORACLE Precompilers.
Even when SQLCODE contains zero, a warning may have been generated. The values of the sqlwarn flags should be checked to determine the type of warning. For Oracle, Sybase and Informix, sqlwarn0 will always be set when the database server has sent a warning back to the application.

5.1.2 The SQLSTATE Variable

DB2
DB2 Universal Database returns SQL-92 compliant SQLSTATE values. DB2 Version 2.1 does not.

The sqlstate variable was introduced in the SQL-92 standard and is the recommended mechanism for future applications. It is divided into two components:

The first two characters are called the class code. Any class code that begins with the letters A through H or the digits 0 through 4 indicates a sqlstate value that is defined by the SQL standard or another standard.
The last three characters are called the subclass code.

A value of "00000" indicates that the previous embedded SQL statement executed successfully.

For specific details of the values returned in SQLSTATE when using Oracle, Sybase or Informix, refer to the relevant Database Error Messages manual. Full details of SQLSTATE values are also given in the online file. Look under SQLSTATE in the help file index.

5.1.3 The Warning Flags

Some statements may cause warnings to be generated. To determine the type of warning, your application should examine the contents of the sqlwarn flags. The value of the flag will be set to "W" if that particular warning occured, otherwise the value will be a blank (space).

Each sqlwarn flag has a specific meaning. For more information on the meaning of the sqlwarn flags, refer to the online help - look under "SQLCA" in the help file index.

5.1.4 The WHENEVER Statement

Explicitly checking the value of sqlcode or sqlstate after each embedded SQL statement can involve writing a lot of code; an alternative is to check the status of the SQL statement by using a WHENEVER statement in your application.

The WHENEVER statement is not an executable statement; it is a directive to the Compiler to generate automatically code that handles errors after each executable embedded SQL statement.

The WHENEVER statement allows one of three default actions (CONTINUE, GOTO or PERFORM) to be registered for each of the following conditions:

Condition	Value of sqlcode
NOT FOUND	100
SQLWARNING	+1
SQLERROR	< 0 (negative)

COBSQL
For Oracle, Sybase and Informix, the 'SQLWARNING' clause will be triggered when sqlwarn0is set to 'W'.

Oracle
When no data is returned from a SELECT or FETCH statement, the condition NOT FOUND is triggered, regardless of the setting of the Oracle precompiler directive MODE.

Informix
Informix allows you to perform a STOP or a CALL from within a WHENEVER statement. These are additions to the ANSI standard and are documented in the Informix ESQL/COBOL programmers manual.

A WHENEVER statement for a particular condition replaces all previous WHENEVER statements for that condition.

The scope of a WHENEVER statement is related to its physical position in the source program, not its logical position in the run sequence. For example, in the following code if the first SELECT statement does not return anything, paragraph A is performed, not paragraph C:

    EXEC SQL
       WHENEVER NOT FOUND PERFORM A
    END-EXEC.
    PERFORM B.
    EXEC SQL
       SELECT col1 into :host-var1 FROM table1 WHERE col2 = :host-var2
    END-EXEC.
 A.
    DISPLAY "First item not found".
 B.
    EXEC SQL
       WHENEVER NOT FOUND PERFORM C.
    END-EXEC.
 C.
    DISPLAY "Second item not found".

5.1.5 SQLERRM

The SQLERRM data area is used to pass error messages to the application from the database server. The SQLERRM data area is split into two parts: SQLERRML and SQLERRMC. SQLERRML holds the length of the error message and SQLERRMC holds the error text. Within an error routine, the following code can be used to display the SQL error message:

IF (SQLERRML > ZERO) and (SQLERRML < 80)
   DISPLAY 'Error Message: ', SQLERRMC(1:SQLERRML)
ELSE
   DISPLAY 'Error Message: ', SQLERRMC
END-IF.

5.1.6 SQLERRD

The SQLERRD data area is an array of six integer status values.

COBSQL
Oracle, Sybase and Informix may set one (or more) of the six values within the SQLERRD array. These indicate how may rows were effected by the SQL statement just executed. For example, SQLERRD(3) holds the total number of rows returned by a SELECT or a series of FETCH statements.

5.2 The SQL Descriptor Area (SQLDA)

Use an SQL Descriptor Area (SQLDA) instead of host variables in the following circumstances:

Dynamic SQL statements
When the number of parameters to be passed or their data types are unknown at compilation time
Static SQL statements
With a cursor FETCH statement.

An SQLDA contains descriptive information about each input parameter or output column:

Column name
Data type
Length
A pointer to the data buffer for each input or output parameter

The SQLDA is unique to each precompiler and ensures that data is converted in the correct format.

Typically, an SQLDA is used with parameter markers to specify input values for prepared SQL statements. However, to receive data from a prepared SELECT statement, you can also use an SQLDA with either the DESCRIBE statement or the INTO option of a PREPARE statement.

The Oracle SQLDA is not compatible with that used by Sybase, OpenESQL or DB2. Similarly, the Sybase, OpenESQL or DB2 SQLDAs are not compatible with the Oracle SQLDA.

COBSQL
For both Oracle and Sybase, the SQLDA is only required if your program uses dynamic SQL.

COBSQL

Oracle, Sybase and Informix do not allow the SQLDA to be included in your program using the following syntax statement:

EXEC SQL
   INCLUDE SQLDA
END-EXEC

For Oracle, Sybase and Informix, the SQLDA must be defined as a standard COBOL copyfile.

COBSQL
Oracle provides an extra copyfile, ORACA, for use with dynamic SQL. This can be included in your program using the following syntax:

EXEC SQL
   INCLUDE ORACA
END-EXEC

You must set the Oracle precompiler option, ORACA=YES before you can use the ORACA. For more information on setting Oracle precompiler options, refer to the Programmer's Guide to the Oracle Precompilers.

COBSQL
Oracle does not supply an SQLDA but the Programmer's Guide to the Oracle Precompilers contains a definition of the layout.

COBSQL
Sybase does not supply an SQLDA copyfile. The Sybase precompiler documentation describes the layout of the SQLDA and how to assign values to the various items within it. The documentaion also describes how to get Sybase to convert between COBOL and Sybase data types.

OpenESQL
The SQLDA structure is supplied in the file sqlda.cpy in the source directory under your Net Express base installation directory. You can include it in your COBOL program by adding the following statement to your data division:

EXEC SQL
   INCLUDE SQLDA
END-EXEC

Full details of the OpenESQL SQLDA are given in the online help file. Look under "SQLDA" in the help file index.

5.2.1 Using the SQLDA

Before an SQLDA structure is used, your application must initialise the following fields:

SQLN	This must be set to the maximum number of SQLVAR entries that the structure can hold.
SQLDABC	The maximum size of the SQLDA. This is calculated as SQLN * 44 + 16

5.2.1.1 The PREPARE and DESCRIBE Statements

You can use the DESCRIBE statement (or the PREPARE statement with the INTO option) to enter the column name, data type, and other data into the appropriate fields of the SQLDA structure.

Before the statement is executed, the SQLN and SQLDABC fields should be initialised as described above.

After the statement has been executed, the SQLD field will contain the number of parameters in the prepared statement. A SQLVAR record is set up for each of the parameters with the SQLTYPE and SQLLEN fields completed.

If you do not know how big the value of SQLN should be, you can issue a DESCRIBE statement with SQLN set to 1 and SQLD set to 0. No column detail information is moved into the SQLDA structure, but the number of columns in the results set is inserted into SQLD.

5.2.1.2 The FETCH Statement

Before performing a FETCH statement using an SQLDA structure, the application must initialize SQLN and SQLDABC as described above. It must then insert into the SQLDATA field the address of each program variable that will receive the data from the corresponding column. (The SQLDATA field is part of SQLVAR). If indicator variables are used, SQLIND must also be set to the corresponding address of the indicator variable.

The data type field (SQLTYPE) and length (SQLLEN) are filled with information from a PREPARE INTO or a DESCRIBE statement. These values can be overwritten by the application prior to a FETCH statement.

5.2.1.3 The OPEN or EXECUTE Statements

To use an SQLDA structure to specify input data to an OPEN or EXECUTE statement, your application must supply the data for the fields of the entire SQLDA structure, including the SQLN, SQLD, SQLDABC, and SQLTYPE, SQLLEN, and SQLDATA fields for each variable. If the value of the SQLTYPE field is an odd number, the address of the indicator variable must also be supplied in SQLIND.

5.2.2 The DESCRIBE Statement

After a PREPARE statement, you can execute a DESCRIBE statement to retrieve information about the data type, length and column name of each column returned by the specified prepared statement. This information is returned in the SQL Descriptor Area (SQLDA):

EXEC SQL
   DESCRIBE stmt1 INTO :sqlda
END-EXEC

If you want to execute a DESCRIBE statement immediately after a PREPARE statement, you can use the INTO option on the PREPARE statement to perform both steps at once:

EXEC SQL
   PREPARE stmt1 INTO :sqlda FROM :stmtbuf
END-EXEC

Cursors

Dynamic SQL