Oracle and 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 defaults to uppercase unless you surround identifiers with double quote characters.

For example, to refer to the SQL Server table called emp, enter the name with double quote characters, as follows:

SQL> SELECT * FROM "emp"@MSQL;

However, to refer to the SQL Server table called emp owned by Scott from an Oracle application, enter the following:

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

If the 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 recommends that you surround all SQL Server object names with double quote characters and use the exact letter case for the object names as they appear in the SQL Server data dictionary. This convention is not required when referring to the supported Oracle data dictionary tables or views listed in Data Dictionary.

If existing applications cannot be changed according to these conventions, create views in Oracle to associate SQL Server names to the correct letter case. For example, to refer to the 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 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 SQL Server database.

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 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.

The gateway does not support using bind variables to update columns of data type LONG.

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-2004";

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-2004")

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. SQL Server processes an empty string as an empty string.

When comparing an empty string the gateway passes literal empty strings to the SQL Server database without any conversion. If you intended an empty string to represent a null value, SQL Server does not process the statement that way; it uses the empty string.

You can 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 * from "emp"@MSQL where "ename" IS NULL;

To select an empty string:

• For VARCHAR columns, the gateway returns an empty string to the Oracle database as NULL value.
• For CHAR columns, the gateway returns the full size of the column with each character as empty space (' ').

For VARCHAR bind variables, the gateway passes empty bind variables to the SQL Server database as a NULL value.