This section describes how you can handle exceptional conditions and warnings in an embedded SQL program. There are two nonexclusive facilities for this.
WHENEVER command.
     sqlca variable.
     
One simple method to catch errors and warnings is to set a specific action to be executed whenever a particular condition occurs. In general:
EXEC SQL WHENEVERconditionaction;
    condition can be one of the following:
    
SQLERROR #The specified action is called whenever an error occurs during the execution of an SQL statement.
SQLWARNING #The specified action is called whenever a warning occurs during the execution of an SQL statement.
NOT FOUND #The specified action is called whenever an SQL statement retrieves or affects zero rows. (This condition is not an error, but you might be interested in handling it specially.)
    action can be one of the following:
    
CONTINUE #This effectively means that the condition is ignored. This is the default.
GOTO labelGO TO label #
        Jump to the specified label (using a C goto
        statement).
       
SQLPRINT #Print a message to standard error. This is useful for simple programs or during prototyping. The details of the message cannot be configured.
STOP #
        Call exit(1), which will terminate the
        program.
       
DO BREAK #
        Execute the C statement break.  This should
        only be used in loops or switch statements.
       
DO CONTINUE #
        Execute the C statement continue.  This should
        only be used in loops statements.  if executed, will cause the flow
        of control to return to the top of the loop.
       
CALL name (args)DO name (args) #
        Call the specified C functions with the specified arguments.  (This
        use is different from the meaning of CALL
        and DO in the normal PostgreSQL grammar.)
       
    The SQL standard only provides for the actions
    CONTINUE and GOTO (and
    GO TO).
   
Here is an example that you might want to use in a simple program. It prints a simple message when a warning occurs and aborts the program when an error happens:
EXEC SQL WHENEVER SQLWARNING SQLPRINT; EXEC SQL WHENEVER SQLERROR STOP;
    The statement EXEC SQL WHENEVER is a directive
    of the SQL preprocessor, not a C statement.  The error or warning
    actions that it sets apply to all embedded SQL statements that
    appear below the point where the handler is set, unless a
    different action was set for the same condition between the first
    EXEC SQL WHENEVER and the SQL statement causing
    the condition, regardless of the flow of control in the C program.
    So neither of the two following C program excerpts will have the
    desired effect:
/*
 * WRONG
 */
int main(int argc, char *argv[])
{
    ...
    if (verbose) {
        EXEC SQL WHENEVER SQLWARNING SQLPRINT;
    }
    ...
    EXEC SQL SELECT ...;
    ...
}
/*
 * WRONG
 */
int main(int argc, char *argv[])
{
    ...
    set_error_handler();
    ...
    EXEC SQL SELECT ...;
    ...
}
static void set_error_handler(void)
{
    EXEC SQL WHENEVER SQLERROR STOP;
}
    For more powerful error handling, the embedded SQL interface
    provides a global variable with the name sqlca
    (SQL communication area)
    that has the following structure:
struct
{
    char sqlcaid[8];
    long sqlabc;
    long sqlcode;
    struct
    {
        int sqlerrml;
        char sqlerrmc[SQLERRMC_LEN];
    } sqlerrm;
    char sqlerrp[8];
    long sqlerrd[6];
    char sqlwarn[8];
    char sqlstate[5];
} sqlca;
    (In a multithreaded program, every thread automatically gets its
    own copy of sqlca.  This works similarly to the
    handling of the standard C global variable
    errno.)
   
    sqlca covers both warnings and errors.  If
    multiple warnings or errors occur during the execution of a
    statement, then sqlca will only contain
    information about the last one.
   
    If no error occurred in the last SQL statement,
    sqlca.sqlcode will be 0 and
    sqlca.sqlstate will be
    "00000".  If a warning or error occurred, then
    sqlca.sqlcode will be negative and
    sqlca.sqlstate will be different from
    "00000".  A positive
    sqlca.sqlcode indicates a harmless condition,
    such as that the last query returned zero rows.
    sqlcode and sqlstate are two
    different error code schemes; details appear below.
   
    If the last SQL statement was successful, then
    sqlca.sqlerrd[1] contains the OID of the
    processed row, if applicable, and
    sqlca.sqlerrd[2] contains the number of
    processed or returned rows, if applicable to the command.
   
    In case of an error or warning,
    sqlca.sqlerrm.sqlerrmc will contain a string
    that describes the error.  The field
    sqlca.sqlerrm.sqlerrml contains the length of
    the error message that is stored in
    sqlca.sqlerrm.sqlerrmc (the result of
    strlen(), not really interesting for a C
    programmer).  Note that some messages are too long to fit in the
    fixed-size sqlerrmc array; they will be truncated.
   
    In case of a warning, sqlca.sqlwarn[2] is set
    to W.  (In all other cases, it is set to
    something different from W.)  If
    sqlca.sqlwarn[1] is set to
    W, then a value was truncated when it was
    stored in a host variable.  sqlca.sqlwarn[0] is
    set to W if any of the other elements are set
    to indicate a warning.
   
    The fields sqlcaid,
    sqlabc,
    sqlerrp, and the remaining elements of
    sqlerrd and
    sqlwarn currently contain no useful
    information.
   
    The structure sqlca is not defined in the SQL
    standard, but is implemented in several other SQL database
    systems.  The definitions are similar at the core, but if you want
    to write portable applications, then you should investigate the
    different implementations carefully.
   
    Here is one example that combines the use of WHENEVER
    and sqlca, printing out the contents
    of sqlca when an error occurs.  This is perhaps
    useful for debugging or prototyping applications, before
    installing a more “user-friendly” error handler.
EXEC SQL WHENEVER SQLERROR CALL print_sqlca();
void
print_sqlca()
{
    fprintf(stderr, "==== sqlca ====\n");
    fprintf(stderr, "sqlcode: %ld\n", sqlca.sqlcode);
    fprintf(stderr, "sqlerrm.sqlerrml: %d\n", sqlca.sqlerrm.sqlerrml);
    fprintf(stderr, "sqlerrm.sqlerrmc: %s\n", sqlca.sqlerrm.sqlerrmc);
    fprintf(stderr, "sqlerrd: %ld %ld %ld %ld %ld %ld\n", sqlca.sqlerrd[0],sqlca.sqlerrd[1],sqlca.sqlerrd[2],
                                                          sqlca.sqlerrd[3],sqlca.sqlerrd[4],sqlca.sqlerrd[5]);
    fprintf(stderr, "sqlwarn: %d %d %d %d %d %d %d %d\n", sqlca.sqlwarn[0], sqlca.sqlwarn[1], sqlca.sqlwarn[2],
                                                          sqlca.sqlwarn[3], sqlca.sqlwarn[4], sqlca.sqlwarn[5],
                                                          sqlca.sqlwarn[6], sqlca.sqlwarn[7]);
    fprintf(stderr, "sqlstate: %5s\n", sqlca.sqlstate);
    fprintf(stderr, "===============\n");
}
The result could look as follows (here an error due to a misspelled table name):
==== sqlca ==== sqlcode: -400 sqlerrm.sqlerrml: 49 sqlerrm.sqlerrmc: relation "pg_databasep" does not exist on line 38 sqlerrd: 0 0 0 0 0 0 sqlwarn: 0 0 0 0 0 0 0 0 sqlstate: 42P01 ===============
SQLSTATE vs. SQLCODE #
    The fields sqlca.sqlstate and
    sqlca.sqlcode are two different schemes that
    provide error codes.  Both are derived from the SQL standard, but
    SQLCODE has been marked deprecated in the SQL-92
    edition of the standard and has been dropped in later editions.
    Therefore, new applications are strongly encouraged to use
    SQLSTATE.
   
    SQLSTATE is a five-character array.  The five
    characters contain digits or upper-case letters that represent
    codes of various error and warning conditions.
    SQLSTATE has a hierarchical scheme: the first
    two characters indicate the general class of the condition, the
    last three characters indicate a subclass of the general
    condition.  A successful state is indicated by the code
    00000.  The SQLSTATE codes are for
    the most part defined in the SQL standard.  The
    PostgreSQL server natively supports
    SQLSTATE error codes; therefore a high degree
    of consistency can be achieved by using this error code scheme
    throughout all applications.  For further information see
    Appendix A.
   
    SQLCODE, the deprecated error code scheme, is a
    simple integer.  A value of 0 indicates success, a positive value
    indicates success with additional information, a negative value
    indicates an error.  The SQL standard only defines the positive
    value +100, which indicates that the last command returned or
    affected zero rows, and no specific negative values.  Therefore,
    this scheme can only achieve poor portability and does not have a
    hierarchical code assignment.  Historically, the embedded SQL
    processor for PostgreSQL has assigned
    some specific SQLCODE values for its use, which
    are listed below with their numeric value and their symbolic name.
    Remember that these are not portable to other SQL implementations.
    To simplify the porting of applications to the
    SQLSTATE scheme, the corresponding
    SQLSTATE is also listed.  There is, however, no
    one-to-one or one-to-many mapping between the two schemes (indeed
    it is many-to-many), so you should consult the global
    SQLSTATE listing in Appendix A
    in each case.
   
    These are the assigned SQLCODE values:
    
ECPG_NO_ERROR) #Indicates no error. (SQLSTATE 00000)
ECPG_NOT_FOUND) #This is a harmless condition indicating that the last command retrieved or processed zero rows, or that you are at the end of the cursor. (SQLSTATE 02000)
When processing a cursor in a loop, you could use this code as a way to detect when to abort the loop, like this:
while (1)
{
    EXEC SQL FETCH ... ;
    if (sqlca.sqlcode == ECPG_NOT_FOUND)
        break;
}
       But WHENEVER NOT FOUND DO BREAK effectively
       does this internally, so there is usually no advantage in
       writing this out explicitly.
      
ECPG_OUT_OF_MEMORY) #
        Indicates that your virtual memory is exhausted.  The numeric
        value is defined as -ENOMEM.  (SQLSTATE
        YE001)
      
ECPG_UNSUPPORTED) #Indicates the preprocessor has generated something that the library does not know about. Perhaps you are running incompatible versions of the preprocessor and the library. (SQLSTATE YE002)
ECPG_TOO_MANY_ARGUMENTS) #This means that the command specified more host variables than the command expected. (SQLSTATE 07001 or 07002)
ECPG_TOO_FEW_ARGUMENTS) #This means that the command specified fewer host variables than the command expected. (SQLSTATE 07001 or 07002)
ECPG_TOO_MANY_MATCHES) #This means a query has returned multiple rows but the statement was only prepared to store one result row (for example, because the specified variables are not arrays). (SQLSTATE 21000)
ECPG_INT_FORMAT) #
       The host variable is of type int and the datum in
       the database is of a different type and contains a value that
       cannot be interpreted as an int.  The library uses
       strtol() for this conversion.  (SQLSTATE
       42804)
      
ECPG_UINT_FORMAT) #
       The host variable is of type unsigned int and the
       datum in the database is of a different type and contains a
       value that cannot be interpreted as an unsigned
       int.  The library uses strtoul()
       for this conversion.  (SQLSTATE 42804)
      
ECPG_FLOAT_FORMAT) #
       The host variable is of type float and the datum
       in the database is of another type and contains a value that
       cannot be interpreted as a float.  The library
       uses strtod() for this conversion.
       (SQLSTATE 42804)
      
ECPG_NUMERIC_FORMAT) #
       The host variable is of type numeric and the datum
       in the database is of another type and contains a value that
       cannot be interpreted as a numeric value.
       (SQLSTATE 42804)
      
ECPG_INTERVAL_FORMAT) #
       The host variable is of type interval and the datum
       in the database is of another type and contains a value that
       cannot be interpreted as an interval value.
       (SQLSTATE 42804)
      
ECPG_DATE_FORMAT) #
       The host variable is of type date and the datum in
       the database is of another type and contains a value that
       cannot be interpreted as a date value.
       (SQLSTATE 42804)
      
ECPG_TIMESTAMP_FORMAT) #
       The host variable is of type timestamp and the
       datum in the database is of another type and contains a value
       that cannot be interpreted as a timestamp value.
       (SQLSTATE 42804)
      
ECPG_CONVERT_BOOL) #
       This means the host variable is of type bool and
       the datum in the database is neither 't' nor
       'f'.  (SQLSTATE 42804)
      
ECPG_EMPTY) #The statement sent to the PostgreSQL server was empty. (This cannot normally happen in an embedded SQL program, so it might point to an internal error.) (SQLSTATE YE002)
ECPG_MISSING_INDICATOR) #A null value was returned and no null indicator variable was supplied. (SQLSTATE 22002)
ECPG_NO_ARRAY) #An ordinary variable was used in a place that requires an array. (SQLSTATE 42804)
ECPG_DATA_NOT_ARRAY) #The database returned an ordinary variable in a place that requires array value. (SQLSTATE 42804)
ECPG_ARRAY_INSERT) #The value could not be inserted into the array. (SQLSTATE 42804)
ECPG_NO_CONN) #The program tried to access a connection that does not exist. (SQLSTATE 08003)
ECPG_NOT_CONN) #The program tried to access a connection that does exist but is not open. (This is an internal error.) (SQLSTATE YE002)
ECPG_INVALID_STMT) #The statement you are trying to use has not been prepared. (SQLSTATE 26000)
ECPG_INFORMIX_DUPLICATE_KEY) #Duplicate key error, violation of unique constraint (Informix compatibility mode). (SQLSTATE 23505)
ECPG_UNKNOWN_DESCRIPTOR) #The descriptor specified was not found. The statement you are trying to use has not been prepared. (SQLSTATE 33000)
ECPG_INVALID_DESCRIPTOR_INDEX) #The descriptor index specified was out of range. (SQLSTATE 07009)
ECPG_UNKNOWN_DESCRIPTOR_ITEM) #An invalid descriptor item was requested. (This is an internal error.) (SQLSTATE YE002)
ECPG_VAR_NOT_NUMERIC) #During the execution of a dynamic statement, the database returned a numeric value and the host variable was not numeric. (SQLSTATE 07006)
ECPG_VAR_NOT_CHAR) #During the execution of a dynamic statement, the database returned a non-numeric value and the host variable was numeric. (SQLSTATE 07006)
ECPG_INFORMIX_SUBSELECT_NOT_ONE) #A result of the subquery is not single row (Informix compatibility mode). (SQLSTATE 21000)
ECPG_PGSQL) #Some error caused by the PostgreSQL server. The message contains the error message from the PostgreSQL server.
ECPG_TRANS) #The PostgreSQL server signaled that we cannot start, commit, or rollback the transaction. (SQLSTATE 08007)
ECPG_CONNECT) #The connection attempt to the database did not succeed. (SQLSTATE 08001)
ECPG_DUPLICATE_KEY) #Duplicate key error, violation of unique constraint. (SQLSTATE 23505)
ECPG_SUBSELECT_NOT_ONE) #A result for the subquery is not single row. (SQLSTATE 21000)
ECPG_WARNING_UNKNOWN_PORTAL) #An invalid cursor name was specified. (SQLSTATE 34000)
ECPG_WARNING_IN_TRANSACTION) #Transaction is in progress. (SQLSTATE 25001)
ECPG_WARNING_NO_TRANSACTION) #There is no active (in-progress) transaction. (SQLSTATE 25P01)
ECPG_WARNING_PORTAL_EXISTS) #An existing cursor name was specified. (SQLSTATE 42P03)