3 Sybase Gateway Features and Restrictions

Return Values and Stored Procedures

By default, all stored procedures and functions do not return a return value to the user. To enable return values, set the HS_FDS_PROC_IS_FUNC parameter in the initialization parameter file.

In the following example, the employee name JOHN SMYTHE is passed to the Sybase stored procedure REVISE_SALARY. The stored procedure retrieves the salary value from the Sybase database to calculate a new yearly salary for JOHN SMYTHE. The revised salary returned in RESULT is used to update EMP in a table of an Oracle database:

DECLARE  INPUT VARCHAR2(15);  RESULT NUMBER(8,2);BEGIN  INPUT := 'JOHN SMYTHE';  RESULT := REVISE_SALARY@SYBS(INPUT);  UPDATE EMP SET SAL = RESULT WHERE ENAME =: INPUT;END;/

The procedural feature automatically converts non-Oracle data types to and from PL/SQL data types.

Result Sets and Stored Procedures

The Oracle Transparent Gateway for Sybase provides support for stored procedures which return result sets.

By default, all stored procedures and functions do not return a result set to the user. To enable result sets, set the HS_FDS_RESULTSET_SUPPORT parameter in the initialization parameter file.

When accessing stored procedures with result sets through the Oracle Transparent Gateway for Sybase, you must work in the sequential mode of Heterogeneous Services.

The Oracle Transparent Gateway for Sybase returns the following information to Heterogeneous Services during procedure description:

• All the input arguments of the remote stored procedure

• None of the output arguments

• One out argument of type ref cursor (corresponding to the first result set returned by the stored procedure)

Client programs have to use the virtual package function dbms_hs_result_set.get_next_result_set to get the ref cursor for subsequent result sets. The last result set returned is the out argument from the procedure.

The limitations of accessing result sets are the following:

• Result sets returned by a remote stored procedure have to be retrieved in the order in which they were placed on the wire

• On execution of a stored procedure, all result sets returned by a previously executed stored procedure will be closed (regardless of whether the data has been completely

In the following example, the Sybase stored procedure is executed to fetch the contents of the emp and dept tables from Sybase:

create procedure REFCURPROC (@arg1 varchar(255), @arg2 varchar(255) output)
as
select @arg2 = @arg1
select * from EMP
select * from DEPT
go

This stored procedure assigns the input parameter arg1 to the output parameter arg2, opens the query SELECT * FROM EMP in ref cursor rc1, and opens the query SELECT * FROM DEPT in ref cursor rc2.

OCIEnv *ENVH;OCISvcCtx *SVCH;OCIStmt *STMH;OCIError *ERRH;OCIBind *BNDH[3];OraText arg1[20];
OraText arg2[255];OCIResult *rset;OCIStmt *rstmt;ub2 rcode[3];ub2 rlens[3];sb2 inds[3];OraText *stmt = (OraText *) "begin refcurproc@SYBS(:1,:2,:3); end;";OraText *n_rs_stm = (OraText *)  "begin :ret := DBMS_HS_RESULT_SET.GET_NEXT_RESULT_SET@SYBS; end;";/* Prepare procedure call statement *//* Handle Initialization code skipped */OCIStmtPrepare(STMH, ERRH, stmt, strlen(stmt), OCI_NTV_SYNTAX, OCI_DEFAULT);/* Bind procedure arguments */inds[0] = 0;strcpy((char *) arg1, "Hello World");rlens[0] = strlen(arg1);OCIBindByPos(STMH, &BNDH[0], ERRH, 1, (dvoid *) arg1, 20, SQLT_CHR,             (dvoid *) &(inds[0]), &(rlens[0]), &(rcode[0]), 0, (ub4 *) 0,              OCI_DEFAULT);
inds[1] = -1;OCIBindByPos(STMH, &BNDH[1], ERRH, 1, (dvoid *) arg2, 20, SQLT_CHR,             (dvoid *) &(inds[1]), &(rlens[1]), &(rcode[1]), 0, (ub4 *) 0,              OCI_DEFAULT);inds[2] = 0;rlens[2] = 0;OCIDescriptorAlloc(ENVH, (dvoid **) &rset, OCI_DTYPE_RSET, 0, (dvoid **) 0);OCIBindByPos(STMH, &BNDH[2], ERRH, 2, (dvoid *) rset, 0, SQLT_RSET,             (dvoid *) &(inds[2]), &(rlens[2]), &(rcode[2]),             0, (ub4 *) 0, OCI_DEFAULT);/* Execute procedure */OCIStmtExecute(SVCH, STMH, ERRH, 1, 0, (CONST OCISnapshot *) 0,               (OCISnapshot *) 0, OCI_DEFAULT);/* Convert result set to statement handle */OCIResultSetToStmt(rset, ERRH);rstmt = (OCIStmt *) rset;/* After this the user can fetch from rstmt *//* Issue get_next_result_set call to get handle to next_result set *//* Prepare Get next result set procedure call */OCIStmtPrepare(STMH, ERRH, n_rs_stm, strlen(n_rs_stm), OCI_NTV_SYNTAX,               OCI_DEFAULT);/* Bind return value */OCIBindByPos(STMH, &BNDH[1], ERRH, 1, (dvoid *) rset, 0, SQLT_RSET,             (dvoid *) &(inds[1]), &(rlens[1]), &(rcode[1]),             0, (ub4 *) 0, OCI_DEFAULT);/* Execute statement to get next result set*/OCIStmtExecute(SVCH, STMH, ERRH, 1, 0, (CONST OCISnapshot *) 0,               (OCISnapshot *) 0, OCI_DEFAULT);/* Convert next result set to statement handle */OCIResultSetToStmt(rset, ERRH);rstmt = (OCIStmt *) rset;/* Now rstmt will point to the second result set returned by theremote stored procedure *//* Repeat execution of get_next_result_set to get the output arguments */

declare  rc1 rcpackage.rctype;  rec1 loc_emp%rowtype;  rc2 rcpackage.rctype;  rec2 loc_dept%rowtype;  rc3 rcpackage.rctype;  rec3 outargs%rowtype;
  out_arg varchar2(255);begin  -- Execute procedure
  out_arg := null;  refcurproc@SYBS('Hello World', out_arg, rc1);  -- Fetch 20 rows from the remote emp table and insert them into loc_emp  for i in 1 .. 20 loop    fetch rc1 into rec1;    insert into loc_emp (rec1.empno, rec1.ename, rec1.job,    rec1.mgr, rec1.hiredate, rec1.sal, rec1.comm, rec1.deptno);  end loop;  -- Close ref cursor  close rc1;  -- Get the next result set returned by the stored procedure  rc2 := dbms_hs_result_set.get_next_result_set@SYBS;  -- Fetch 5 rows from the remote dept table and insert them into loc_dept  for i in 1 .. 5 loop    fetch rc2 into rec2;    insert into loc_dept values (rec2.deptno, rec2.dname, rec2.loc);  end loop;  --Close ref cursor  close rc2;  -- Get the output arguments from the remote stored procedure  -- Since we are in sequential mode, they will be returned in the  -- form of a result set  rc3 := dbms_hs_result_set.get_next_result_set@SYBS;  -- Fetch them and insert them into the outarguments table  fetch rc3 into rec3;  insert into outargs (rec3.outarg, rec3.retval);  -- Close ref cursor  close rc3;end;
/

Chained Mode

The gateway supports the ANSI-standard chained mode. Sybase stored procedures must be written for this mode. Running in chained mode allows the gateway to extend the Oracle two-phase commit protection to transactions updating Oracle and Sybase databases.

Column Definitions

By default, a Sybase table column cannot contain null values unless NULL is specified in the column definition. In compliance with the ANSI standard, the Sybase database option "allow nulls by default" can be set to true to change the default column definition to NULL.

For an Oracle table, null values are allowed in a column unless NOT NULL is specified in the column definition.

Naming Rules

Naming rule issues include the following:

• Rules for Naming Objects

• Case Sensitivity

SQL> SELECT * FROM "emp"@SYBS;

SQL> SELECT * FROM "Scott"."emp"@SYBS;

SQL> SELECT * FROM SCOTT."emp"@SYBS;

SQL> SELECT * FROM scott."emp"@SYBS;

SQL> CREATE VIEW EMP (EMPNO, ENAME, SAL, HIREDATE)      AS SELECT "empno", "ename", "sal", "hiredate"      FROM "emp"@SYBS;

SQL> SELECT EMPNO, ENAME FROM EMP;

Data Types

Data type issues include the following:

• Binary Literal Notation

• Data Type Conversion

SQL> INSERT INTO BINARY_TAB@SYBS VALUES ('0xff')

SELECT DATE_COL FROM TEST@SYBS WHERE DATE_COL = "1-JAN-2001";

SELECT DATE_COL FROM TEST@SYBS WHERE DATE_COL = TO_DATE("1-JAN-2001")

Queries

Query issues include the following:

• Row Selection

• Empty Strings

• Empty Bind Variables

SELECT * from "emp"@SYBS where "ename" IS NULL;

Locking

The locking model for an Sybase database differs significantly from the Oracle model. The gateway depends on the underlying Sybase behavior, so Oracle applications that access Sybase through the gateway can be affected by the following possible scenarios:

• Read access might block write access

• Write access might block read access

• Statement-level read consistency is not guaranteed

  See Also:

  Sybase documentation for information about the Sybase locking model.

Transactional Integrity

The gateway cannot guarantee transactional integrity in the following cases:

• When a statement that is processed by the gateway causes an implicit commit in the target database

• When the target database is configured to work in autocommit mode

  Note:

  Oracle corporation strongly recommends the following:

  • If you know that executing a particular statement causes an implicit commit in the target database, then ensure that this statement is executed in its own transaction.

  • Do not configure the target database to work in autocommit mode.

Transaction Capability

The gateway does not support savepoints. If a distributed update transaction is under way involving the gateway and a user attempts to create a savepoint, the following error occurs:

ORA-02070: database dblink does not support savepoint in this context

By default, the gateway is configured as COMMIT_CONFIRM and it is always the commit point site when the Sybase database is updated by the transaction.

COMMIT or ROLLBACK in PL/SQL Cursor Loops Closes Open Cursors

Any COMMIT or ROLLBACK issued in a PL/SQL cursor loop closes all open cursors, which can result in the following error:

ORA-1002:  fetch out of sequence 

To prevent this error, move the COMMIT or ROLLBACK statement outside the cursor loop.

Stored Procedures

Changes issued through stored procedures that embed commits or rollbacks cannot be controlled by the Oracle transaction manager or Oracle COMMIT or ROLLBACK commands.

When accessing stored procedures with result sets through the Oracle Transparent Gateway for Sybase, you must work in the sequential mode of Heterogeneous Services.

When accessing stored procedures with multiple result sets through the Oracle Transparent Gateway for Sybase, you must read all the result sets before continuing.

Output parameters of stored procedures must be initialized to a NULL value.

You cannot use RETURN_VALUE nor RETURNVALUE as the names for any input or output parameters of stored procedures.

Pass-Through Feature

DDL statements executed by Sybase using the gateway pass-through feature might fail if they are in a multi-statement transaction. Set the Sybase option "ddl in tran" to allow DDL statements in a transaction.

Oracle Corporation recommends that you place a DDL statement in its own transaction when executing such a statement with the pass-through feature. An explicit COMMIT must be issued after the DDL statement.

If the SQL statements being passed through the gateway result in an implicit commit at the Sybase database, the Oracle transaction manager is unaware of the commit and an Oracle ROLLBACK command cannot be used to roll back the transaction.

Sybase NCHAR and NVARCHAR Data Types

The gateway cannot select a column defined with a Sybase NCHAR or NVARCHAR data type.

SQL Syntax

This section lists restrictions on the following SQL syntax:

• WHERE CURRENT OF Clause

• CONNECT BY Clause

• ROWID

• Subqueries in INSERT Statement

• EXPLAIN PLAN Statement

  See Also:

  Appendix B, "Supported SQL Syntax and Functions" for more information about restrictions on SQL syntax.

SQL> INSERT INTO "emp_target"@SYBS
         SELECT a."empno" FROM "emp_source"@SYBS a,
            "emp_source"@SYBS b WHERE b."empno"=9999

SQL*Plus COPY Command with Lowercase Table Names

You need to use double quotes to wrap around lower case table names.

For example:

copy from tkhouser/tkhouser@inst1 insert loc_tkhodept using select * from "tkhodept"@holink2;

Database Links

The gateway is not multithreaded and cannot support shared database links. Each gateway session spawns a separate gateway process and connections cannot be shared.

FLOAT Data Type

The FLOAT data type precision is (7).

VARBINARY Data Type

The VARBINARY data type is reported as BINARY.

Encrypted Format Login

Oracle database server no longer supports the initialization parameter DBLINK_ENCRYPT_LOGIN. Up to version 7.3, this parameter's default TRUE value prevented the password for the login user ID from being sent over the network (in the clear). Later versions automatically encrypt the password.

Date Arithmetic

The following SQL expressions do not function correctly with the gateway:

date + numbernumber + datedate - numberdate1 - date2

Statements with the preceding expressions are sent to the Sybase database without any translation. Since Sybase does not support these date arithmetic functions, the statements return an error.

Sybase IMAGE and TEXT Data Type

The following restrictions apply when using IMAGE and TEXT data types:

• An unsupported SQL function cannot be used in a SQL statement that accesses a column defined as Sybase data type IMAGE or TEXT.

• You cannot use SQL*Plus to select data from a column defined as Sybase data type IMAGE or TEXT when the data is greater than 80 characters in length. Oracle Corporation recommends using Pro*C or Oracle Call Interface to access such data in a Sybase database.

• IMAGE and TEXT data types must be NULLABLE for INSERT or UPDATE to work.

• A table including a IMAGE or TEXT column must have a unique index defined on the table or the table must have a separate column that serves as a primary key.

• IMAGE and TEXT data cannot be read through pass-through queries.

The gateway does not support the PL/SQL function COLUMN_VALUE_LONG of the DBMS_SQL package.

String Functions

If you concatenate numeric literals using the "||" operator when using the gateway to query a Sybase database, the result is an arithmetic addition. For example, the result of the following statement is 18:

SQL> SELECT 9 || 9 FROM DUAL@SYBS;

The result is 99 when using Oracle to query an Oracle database.

Schema Names and PL/SQL

If you do not prefix a Sybase database object with its schema name in a SQL statement within a PL/SQL block, the following error message occurs:

ORA-6550 PLS-201 Identifier table_name must be declared.

Change the SQL statement to include the schema name of the object.

Data Dictionary Views and PL/SQL

You cannot refer to data dictionary views in SQL statements that are inside a PL/SQL block.

Stored Procedures

Stored procedures with output parameters defined with a CHAR data type return output parameters with VARCHAR data types.

Stored procedures with input or output parameters defined with NUMERIC or DECIMAL data types that are passed with either a NULL value or no value for input will return output values without the fractional part. To prevent this from happening, always specify an input parameter value, even if it is not used.

Return values of stored procedures which return result sets are incorrect.