Release 8.1.6 for Windows NT
Part Number A82868-01
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| Oracle Transparent Gateway Microsoft SQL Server Administrator's Guide Release 8.1.6 for Windows NT Part Number A82868-01 |
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This chapter contains information specific to this release of the Oracle Transparent Gateway for Microsoft SQL Server, and contains the following sections:
This table lists the versions of the components included on the distribution CD-ROM. All components are at production level.
This section describes the following:
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The following table summarizes the hardware requirements for the Oracle Transparent Gateway for Microsoft SQL Server.
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The system software configuration described in this section is supported by Oracle Corporation as long as the underlying system software products are supported by their respective vendors. Verify the latest support status with your system software vendors.
The following table summarizes the software requirements for the Oracle Transparent Gateway for Microsoft SQL Server.
The following table provides the tested configurations at Oracle, at the time of this document release. Oracle continues to provide support for the most recent releases of Oracle and non-Oracle systems in a timely manner. For current supported configuration information, please contact Oracle Support Services or visit http://www.oracle.com/gateways.
Microsoft SQL Server and Oracle databases function differently in some areas, causing compatibility problems. The following compatibility issues are described in this section:
The gateway supports the ANSI-standard chained mode. Microsoft SQL Server 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 Microsoft SQL Server databases.
By default, Oracle assumes all columns can contain null values. Microsoft SQL Server assumes all columns cannot contain null values unless you set a Microsoft SQL Server option to override this default.
Naming rule issues include the following:
Oracle and Microsoft SQL Server use different database object naming rules. For example, the maximum number of characters allowed for each object name can be different. Also, the use of single and double quote marks, case sensitivity, and the use of alphanumeric characters can all be different.
The Oracle database server defaults to uppercase unless you surround identifiers with double quote characters. For example, to refer to a Microsoft SQL Server table called emp, enter the name with double quote characters as follows:
SQL> SELECT * FROM "emp"@MSQL;
However, to refer to a Microsoft SQL Server table called emp owned by Scott from an Oracle application, enter the following:
SQL> SELECT * FROM "Scott"."emp"@MSQL;
If the Microsoft SQL Server table called emp is owned by SCOTT, a table owner name in uppercase letters, you can enter the owner name without double quote characters as follows:
SQL> SELECT * FROM SCOTT."emp"@MSQL;
or
SQL> SELECT * FROM scott."emp"@MSQL;
Oracle Corporation recommends that you surround all Microsoft SQL Server object names with double quote characters and use the exact letter case for the object names as they appear in the Microsoft SQL Server data dictionary. This convention is not required when referring to the supported Oracle data dictionary tables or views listed in Appendix B, "Data Dictionary".
If existing applications cannot be changed according to these conventions, create views in Oracle to associate Microsoft SQL Server names to the correct letter case. For example, to refer to the Microsoft SQL Server table emp from an existing Oracle application by using only uppercase names, define the following view:
SQL> CREATE VIEW EMP (EMPNO, ENAME, SAL, HIREDATE)
AS SELECT "empno", "ename", "sal", "hiredate"
FROM "emp"@MSQL;
With this view, the application can issue statements such as the following:
SQL> SELECT EMPNO, ENAME FROM EMP;
Using views is a workaround solution that duplicates data dictionary information originating in the Microsoft SQL Server data dictionary. You must be prepared to update the Oracle view definitions whenever the data definitions for the corresponding tables are changed in the Microsoft SQL Server database.
Data type issues include the following:
Oracle SQL uses hexadecimal digits surrounded by single quotes to express literal values being compared or inserted into columns defined as data type RAW.
This notation is not converted to syntax compatible with the Microsoft SQL Server VARBINARY and BINARY data types (a 0x followed by hexadecimal digits surrounded by single quotes).
For example, the following statement is not supported:
SQL> INSERT INTO BINARY_TAB@MSQL VALUES ('0xff')
where BINARY_TAB contains a column of data type VARBINARY or BINARY. Use bind variables when inserting into or updating VARBINARY and BINARY data types.
Microsoft SQL Server does not support implicit date conversions. Such conversions must be explicit.
For example, the gateway issues an error for the following SELECT statement:
SELECT DATE_COL FROM TEST@MSQL WHERE DATE_COL = "1-JAN-1998";
To avoid problems with implicit conversions, add explicit conversions, as in the following:
SELECT DATE_COL FROM TEST@MSQL WHERE DATE_COL = TO_DATE("1-JAN-1998")
Query issues include the following:
Microsoft SQL Server evaluates a query condition for all selected rows before returning any of the rows. If there is an error in the evaluation process for one or more rows, no rows are returned even though the remaining rows satisfy the condition.
Oracle evaluates the query condition row by row and returns a row when the evaluation is successful. Rows are returned until a row fails the evaluation.
Oracle processes an empty string in a SQL statement as a null value. Microsoft SQL Server processes an empty string as a single space. For example, the following statement:
SELECT "ename", "empno", "job" FROM "emp"@MSQL
WHERE "ename" = '';
is processed by Microsoft SQL Server as follows:
SELECT ename, empno, job FROM emp WHERE ename = ' '
The gateway passes the empty string to the Microsoft SQL Server database without any conversion. If you intended an empty string to represent a null value, Microsoft SQL Server does not process the statement that way; it uses a space value. Avoid this problem by using NULL or IS NULL in the SQL statement instead of the empty string syntax, as in the following example:
SELECT "ename", "empno", "job" FROM "emp"@MSQL
WHERE "ename" IS NULL;
The gateway returns an empty string to the Oracle database server as a NULL value. This applies only to columns defined with a VARCHAR data type.
The gateway passes empty bind variables to the Microsoft SQL Server database as a NULL value. This applies only to columns defined with a VARCHAR data type.
The locking model for a Microsoft SQL Server database differs significantly from the Oracle model. The gateway depends on the underlying Microsoft SQL Server behavior, so Oracle applications that access Microsoft SQL Server through the gateway can be affected by the following possible scenarios:
Oracle Transparent Gateway for Microsoft SQL Server, Version 8.1.6, is architecturally different from the earlier versions of the gateway. If you encounter incompatibility problems not listed in this section or in "Known Problems" on page 1-15, please contact Oracle Support Services. The following section describes the known restrictions and includes suggestions for dealing with them when possible:
The following restrictions also apply:
The gateway cannot guarantee transactional integrity in the following cases:
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
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.
Changes issued through stored procedures that embed commits or rollbacks cannot be controlled by the Oracle transaction manager or Oracle COMMIT or ROLLBACK commands.
Stored procedures that return a result set can be executed, but the result set is skipped. Any output parameters and return values are returned.
If the SQL statements being passed through the gateway result in an implicit commit at the Microsoft SQL Server database, the Oracle transaction manager is unaware of the commit and an Oracle ROLLBACK command cannot be used to roll back the transaction.
Microsoft SQL Server requires some DDL statements to be executed in their own transaction, and only one DDL statement can be executed in a given transaction.
If you use these DDL statements in a Microsoft SQL Server stored procedure and you execute the stored procedure through the gateway using the procedural feature, or, if you execute the DDL statements through the gateway using the pass-through feature, an error condition might result. This is because the procedural feature and the pass-through feature of the gateway cannot guarantee that the DDL statements are executed in their own separate transaction.
The following Microsoft SQL Server DDL statements can cause an error condition if you attempt to pass them with the gateway pass-through feature, or if you execute a Microsoft SQL Server stored procedure that contains them:
This section lists restrictions on the following SQL syntax:
Appendix A, "Supported SQL Syntax and Functions" for more information about restrictions on SQL syntax.
See Also:
The SELECT FOR UPDATE statement is not supported.
UPDATE and DELETE statements with the WHERE CURRENT OF clause are not supported because they rely on the Oracle ROWID implementation. To update or delete a specific row through the gateway, a condition style WHERE clause must be used.
The gateway does not support the CONNECT BY clause in a SELECT statement.
Subqueries in the SET clause of an UPDATE statement are not supported.
Subqueries can be specified in the WHERE clause of an UPDATE statement. Each subquery, however, must reference a Microsoft SQL Server table. For example, using the table GTW_EMP, the following statement results in a 10% salary increase for all employees working in the RESEARCH department:
SQL> UPDATE "GTW_EMP"@SYBS SET "SAL"="SAL" * 1.1 2 WHERE "DEPTNO"=(SELECT "DEPTNO" FROM "GTW_DEPT"@MSQL 3 WHERE "DNAME"='RESEARCH');
If "GTW_DEPT"@MSQL is replaced by "DEPT" in the subquery where DEPT is the same table but located in the Oracle database, the following error results after the statement is issued:
ORA-02025: All tables in the SQL statement must be at the remote database.
The Oracle ROWID implementation is not supported.
TO_DATE is a reserved word and cannot be used as a database identifier name.
In a PL/SQL block, all Microsoft SQL Server database objects owned by a Microsoft SQL Server database owner must be prefixed with the database owner's user ID. This user ID, dbo, must be enclosed in double quote characters. The Oracle database server prefixes all Microsoft SQL Server database objects with the Microsoft SQL Server login user ID specified in the database link for the gateway. However, these user IDs are not the same value, which means that Oracle uses the wrong prefix value.
To solve this problem, use the database owner's user ID to prefix objects referred to in the SQL statements instead of allowing Oracle to add the prefix. For example, for a Microsoft SQL Server database owner, the following SELECT statement is correct:
SELECT "name" INTO report_name FROM "dbo"."sysusers"@MSQL
WHERE "uid" = 1;
Not using the database owner's user ID in SQL statements results in the following error messages:
ERROR at line line_number
ORA-06550: line line_number, column col:
PLS-00701: identifier 'sysusers' must be declared
ORA-06550: line line_number, column col:
PL/SQL: SQL statement ignored
The gateway does not support the SQL*Plus COPY command for lowercase table names.
The gateway is not multithreaded and cannot support shared database links. Each gateway session spawns a separate gateway process and connections cannot be shared.
The gateway supports all single byte ASCII character sets and the following multibyte character sets:
This section describes known problems and includes suggestions for correcting them when possible. If you have any questions or concerns about the problems, contact Oracle Support Services. A current list of problems is available online. Contact your local Oracle Corporation office for information about accessing the list.
The following known problems are described in this section:
The FLOAT data type precision is (7).
The VARBINARY data type is reported as BINARY.
The Oracle database server supports an Oracle initialization parameter, DBLINK_ENCRYPT_LOGIN. When this parameter is set to TRUE, the password for the login user ID is not sent over the network.
If this parameter is set to TRUE in the initialization parameter file used by the Oracle database server, you must change the setting to FALSE to allow Oracle to communicate with the gateway.
The Oracle database server does not send the gateway a SELECT statement containing an aggregate function that is part of a CREATE TABLE or CREATE VIEW statement. For example, it does not send the following statement:
CREATE TABLE sum_calls_table AS
SELECT SUM(calls_abandoned), SUM(calls_completed),
SUM(calls_failed) FROM monthly_calls@MSQL;
Instead, Oracle interprets what the SQL statement requests and sends the gateway a statement or statements to retrieve the data required for the request. After the data is retrieved, Oracle performs the aggregate function originally requested and passes the results to the application.
A solution to this problem is to use a different series of SQL statements. For example, instead of using the CREATE TABLE statement in the above example, use the following statements:
DROP TABLE sum_calls_table;
CREATE TABLE sum_calls_table (x1sum NUMBER, x2sum NUMBER,
x3sum NUMBER);
DECLARE
x1 NUMBER;
x2 NUMBER;
x3 NUMBER;
BEGIN
SELECT SUM(calls_abandoned), SUM(calls_completed),
SUM(calls_failed) INTO x1, x2, x3 FROM monthly_calls@MSQL;
INSERT INTO sum_calls_table VALUES (x1, x2, x3);
END;
/
The following SQL expressions do not function correctly with the gateway:
date + number
number + date
date - number
date1 - date2
Statements with the above expressions are sent to the Microsoft SQL Server database without any translation. Since Microsoft SQL Server does not support these date arithmetic functions, the statements return an error.
The following restrictions apply when using IMAGE and TEXT data types:
The gateway does not support the PL/SQL function COLUMN_VALUE_LONG of the DBMS_SQL package.
If you concatenate numeric literals using the "||" or CONCAT operator when using the gateway to query a Microsoft SQL Server database, the result is an arithmetic addition. For example, the result of the following statement is 18:
SQL> SELECT 9 || 9 FROM "DUAL"@MSQL;
The result is 99 when using Oracle to query an Oracle database.
If you do not prefix a Microsoft SQL Server 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.
You cannot refer to data dictionary views in SQL statements that are inside a PL/SQL block.
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.
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