|Oracle® Transparent Gateway for Microsoft SQL Server Administrator's Guide
10g Release 1 (10.1) for Microsoft Windows
Part Number B10544-01
After the gateway is installed and configured, you can use the gateway to access Microsoft SQL Server data, pass Microsoft SQL Server commands from applications to the Microsoft SQL Server database, perform distributed queries, and copy data.
This chapter contains the following sections:
The gateway can pass Microsoft SQL Server commands or statements from the application to the Microsoft SQL Server database using the DBMS_HS_PASSTHROUGH package.
Use the DBMS_HS_PASSTHROUGH package in a PL/SQL block to specify the statement to be passed to the Microsoft SQL Server database, as follows:
DECLARE num_rows INTEGER; BEGIN num_rows := DBMS_HS_PASSTHROUGH.EXECUTE_IMMEDIATE@MSQL('command'); END; /
Where command cannot be one of the following:
The DBMS_HS_PASSTHROUGH package supports passing bind values and executing SELECT statements.
Using the procedural feature, the gateway can execute stored procedures that are defined in the Microsoft SQL Server database. It is not necessary to relink the gateway or define the procedure to the gateway, but the procedure's access privileges must permit access by the user that the gateway is logging in as.
Standard PL/SQL statements are used to execute a stored procedure.
User-defined functions in a remote non-Oracle database can be used in SQL statements.
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.
Appendix D, "Heterogeneous Services Initialization Parameters" for information about both editing the initialization parameter file and the HS_FDS_PROC_IS_FUNC parameter.
In the following example, the employee name JOHN SMYTHE is passed to the Microsoft SQL Server stored procedure REVISE_SALARY. The stored procedure retrieves the salary value from the Microsoft SQL Server 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@MSQL(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.
The Oracle Transparent Gateway for Microsoft SQL Server 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.
Appendix D, "Heterogeneous Services Initialization Parameters" for information about both editing the initialization parameter file and the HS_FDS_RESULTSET_SUPPORT parameter. For further information about Oracle support for result sets in non-Oracle databases see Oracle Database Heterogeneous Connectivity Administrator's Guide.
When accessing stored procedures with result sets through the Oracle Transparent Gateway for Microsoft SQL Server, you must work in the sequential mode of Heterogeneous Services.
The Oracle Transparent Gateway for Microsoft SQL Server returns the following information to Heterogeneous Services during procedure description:
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:
In the following example, the Microsoft SQL Server stored procedure is executed to fetch the contents of the emp and dept tables from Microsoft SQL Server:
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.
The following example shows OCI program fetching from result sets in sequential mode:
OCIEnv *ENVH; OCISvcCtx *SVCH; OCIStmt *STMH; OCIError *ERRH; OCIBind *BNDH; OraText arg1; OraText arg2; OCIResult *rset; OCIStmt *rstmt; ub2 rcode; ub2 rlens; sb2 inds; OraText *stmt = (OraText *) "begin refcurproc@MSQL(:1,:2,:3); end;"; OraText *n_rs_stm = (OraText *) "begin :ret := DBMS_HS_RESULT_SET.GET_NEXT_RESULT_SET@MSQL; 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; strcpy((char *) arg1, "Hello World"); rlens = strlen(arg1); OCIBindByPos(STMH, &BNDH, ERRH, 1, (dvoid *) arg1, 20, SQLT_CHR, (dvoid *) &(inds), &(rlens), &(rcode), 0, (ub4 *) 0, OCI_DEFAULT); inds = -1; OCIBindByPos(STMH, &BNDH, ERRH, 1, (dvoid *) arg2, 20, SQLT_CHR, (dvoid *) &(inds), &(rlens), &(rcode), 0, (ub4 *) 0, OCI_DEFAULT); inds = 0; rlens = 0; OCIDescriptorAlloc(ENVH, (dvoid **) &rset, OCI_DTYPE_RSET, 0, (dvoid **) 0); OCIBindByPos(STMH, &BNDH, ERRH, 2, (dvoid *) rset, 0, SQLT_RSET, (dvoid *) &(inds), &(rlens), &(rcode), 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, ERRH, 1, (dvoid *) rset, 0, SQLT_RSET, (dvoid *) &(inds), &(rlens), &(rcode), 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 the remote stored procedure */ /* Repeat execution of get_next_result_set to get the output arguments */
Assume that the table loc_emp is a local table exactly like the Microsoft SQL Server emp table. The same assumption applies for loc_dept. outargs is a table with columns corresponding to the out arguments of the Microsoft SQL Server stored procedure.
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@MSQL('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@MSQL; -- 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@MSQL; -- 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; /
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 implicit transactions. Microsoft SQL Server stored procedures must be written for this mode. Running implicit transactions allows the gateway to extend the Oracle two-phase commit protection to transactions updating Oracle and Microsoft SQL Server databases.
By default, a Microsoft SQL Server table column cannot contain null values unless NULL is specified in the column definition. Microsoft SQL Server assumes all columns cannot contain null values unless you set a Microsoft SQL Server option to override this default.
For an Oracle table, null values are allowed in a column unless NOT NULL is specified in the column definition.
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 quotation 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 the Microsoft SQL Server table called emp, enter the name with double quote characters, as follows:
However, to refer to the Microsoft SQL Server table called emp owned by Scott from an Oracle application, enter the following:
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:
Oracle 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 C, "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:
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:
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.
The gateway does not support using bind variables to update columns of data type LONG.
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:
To avoid problems with implicit conversions, add explicit conversions, as in the following:
Appendix A, "Data Type Conversion" for more information about restrictions on data types.
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:
is processed by Microsoft SQL Server as follows:
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:
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 an 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:
If you encounter incompatibility problems not listed in this section or in "Known Problems", please contact Oracle Support Services. The following section describes the known restrictions and includes suggestions for dealing with them when possible:
The gateway uses Microsoft ODBC driver to talk to Microsoft SQL Server. Microsoft's ODBC driver has the limitation that only one open statement or cursor is allowed for each connection. If a second statement or cursor needs to open in the same transaction to access SQL Server, it requires a new connection.
Because of this limitation multiple open statements or cursors within the same transaction can lock each other because they use different connections to Microsoft SQL Server.
To avoid this restriction, issue a commit, or modify the logic, or both.
The gateway cannot guarantee transactional integrity in the following cases:
The gateway sets Autocommit Mode to Off when a connection is established to the Microsoft SQL Server database.
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:
By default, the gateway is configured as COMMIT_CONFIRM.
Any COMMIT or ROLLBACK issued in a PL/SQL cursor loop closes all open cursors, which can result in the following error:
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.
When accessing stored procedures with result sets through the Oracle Transparent Gateway for Microsoft SQL Server, you must work in the sequential mode of Heterogeneous Services.
When accessing stored procedures with multiple result sets through the Oracle Transparent Gateway for Microsoft SQL Server, you must read all the result sets before continuing.
Output parameters of stored procedures must be initialized to an empty string.
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:
UPDATE and DELETE statements with the WHERE CURRENT OF clause are not supported by the gateway 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.
Bind variables and expressions are not supported as operands in string functions or mathematical functions, when part of subquery in an INSERT, UPDATE or DELETE SQL statement.
Due to a limitation in Microsoft SQL Server, you cannot use parameters in subqueries.
Subqueries, data dictionary tables and views 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"@MSQL 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:
Data dictionary tables and views in the SET clause of an UPDATE statement are not supported.
The Oracle ROWID implementation is not supported.
TO_DATE is a reserved word and cannot be used as a database identifier name.
The EXPLAIN PLAN statement is not supported.
The following restrictions apply to using functions:
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.
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 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 Oracle9i database server (Release 9.2 and earlier) supported 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 Oracle9i database server, you must change the setting to FALSE, the default setting, to allow Oracle9i to communicate with the gateway.
In the current release, Oracle Database 10g, Release 10.1, the DBLINK_ENCRYPT_LOGIN initialization parameter is obsolete, so you need not check it.
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 preceding 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:
Statements with the preceding 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, TEXT and NTEXT data types:
The gateway does not support the PL/SQL function COLUMN_VALUE_LONG of the DBMS_SQL package.
Appendix B, "Supported SQL Syntax and Functions" for more information about restrictions on SQL syntax.
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:
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:
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.