20
Reference Information

This chapter contains detailed JDBC reference information, including the following topics:

• Valid SQL-JDBC Datatype Mappings
• Supported SQL and PL/SQL Datatypes
• Embedded SQL92 Syntax
• Oracle JDBC Notes and Limitations
• Related Information

Valid SQL-JDBC Datatype Mappings

Table 3-2 in Chapter 3 describes the default mappings between Java classes and SQL datatypes supported by the Oracle JDBC drivers. Compare the contents of the JDBC Datatypes, Standard Java Types and SQL Datatypes columns in Table 3-2 with the contents of Table 20-1 below.

Table 20-1 lists all the possible Java types to which a given SQL datatype can be validly mapped. The Oracle JDBC drivers will support these "non-default" mappings. For example, to materialize SQL CHAR data in an oracle.sql.CHAR object use the getCHAR() method. To materialize it as a java.math.BigDecimal object, use the getBigDecimal() method.

Table 20-1 Valid SQL Datatype-Java Class Mappings  

Supported SQL and PL/SQL Datatypes

The tables in this section list SQL and PL/SQL datatypes, and whether the Oracle JDBC drivers and SQLJ support them. Table 20-2 describes Oracle JDBC driver and SQLJ support for SQL datatypes.

Table 20-2 Support for SQL Datatypes  

Table 20-3 describes Oracle JDBC driver and SQLJ support for the ANSI-supported SQL datatypes.

Table 20-3 Support for ANSI-92 SQL Datatypes  

Table 20-4 describes Oracle JDBC driver and SQLJ support for SQL User-Defined types.

Table 20-4 Support for SQL User-Defined Types 

Table 20-5 describes Oracle JDBC driver and SQLJ support for PL/SQL datatypes. Note that PL/SQL datatypes include these categories:

• scalar types
• scalar character types (includes boolean and date datatypes)
• composite types
• reference types
• LOB types

Table 20-5 Support for PL/SQL Datatypes  

Embedded SQL92 Syntax

Oracle's JDBC drivers support some embedded SQL92 syntax. This is the syntax that you specify between curly braces. The current support is basic. This section describes the support offered by the drivers for the following SQL92 constructs:

• Time and Date Literals
• Scalar Functions
• LIKE Escape Characters
• Outer Joins
• Function Call Syntax

Where driver support is limited, these sections also describe possible workarounds.

Disabling Escape Processing

Escape processing for SQL92 syntax is enabled by default, which results in the JDBC driver performing escape substitution before sending the SQL code to the database. If you want the driver to use regular Oracle SQL syntax, which is more efficient than SQL92 syntax and escape processing, then use this statement:

stmt.setEscapeProcessing(false);

Time and Date Literals

Databases differ in the syntax they use for date, time, and timestamp literals. JDBC supports dates and times written only in a specific format. This section describes the formats you must use for date, time, and timestamp literals in SQL statements.

Date Literals

The JDBC drivers support date literals in SQL statements written in the format:

{d 'yyyy-mm-dd'}

Where yyyy-mm-dd represents the year, month, and day--for example:

{d '1995-10-22'}

The JDBC drivers will replace this escape clause with the equivalent Oracle representation: "22 OCT 1995".

This code snippet contains an example of using a date literal in a SQL statement.

// Connect to the database
// You can put a database name after the @ sign in the connection URL.
Connection conn = DriverManager.getConnection
                  ("jdbc:oracle:oci:@", "scott", "tiger");

// Create a Statement
Statement stmt = conn.createStatement ();

// Select the ename column from the emp table where the hiredate is Jan-23-1982
ResultSet rset = stmt.executeQuery 
                 ("SELECT ename FROM emp WHERE hiredate = {d '1982-01-23'}");

// Iterate through the result and print the employee names
while (rset.next ())
   System.out.println (rset.getString (1));

Time Literals

The JDBC drivers support time literals in SQL statements written in the format:

{t 'hh:mm:ss'}

where hh:mm:ss represents the hours, minutes, and seconds--for example:

{t '05:10:45'}

The JDBC drivers will replace this escape clause with the equivalent Oracle representation: "05:10:45".

If the time is specified as:

{t '14:20:50'}

Then the equivalent Oracle representation would be "14:20:50", assuming the server is using a 24-hour clock.

This code snippet contains an example of using a time literal in a SQL statement.

ResultSet rset = stmt.executeQuery 
                 ("SELECT ename FROM emp WHERE hiredate = {t '12:00:00'}");

Timestamp Literals

The JDBC drivers support timestamp literals in SQL statements written in the format:

{ts 'yyyy-mm-dd hh:mm:ss.f...'} 

where yyyy-mm-dd hh:mm:ss.f... represents the year, month, day, hours, minutes, and seconds. The fractional seconds portion (".f...") is optional and can be omitted. For example: {ts '1997-11-01 13:22:45'} represents, in Oracle format, NOV 01 1997 13:22:45.

This code snippet contains an example of using a timestamp literal in a SQL statement.

ResultSet rset = stmt.executeQuery 
    ("SELECT ename FROM emp WHERE hiredate = {ts '1982-01-23 12:00:00'}");

Scalar Functions

The Oracle JDBC drivers do not support all scalar functions. To find out which functions the drivers support, use the following methods supported by the Oracle-specific oracle.jdbc.OracleDatabaseMetaData class and the standard Java java.sql.DatabaseMetadata interface:

• getNumericFunctions(): Returns a comma-separated list of math functions supported by the driver. For example, ABS(number), COS(float), SQRT(float).
• getStringFunctions(): Returns a comma-separated list of string functions supported by the driver. For example, ASCII(string), LOCATE(string1, string2, start).
• getSystemFunctions(): Returns a comma-separated list of system functions supported by the driver. For example, DATABASE(), IFNULL(expression, value), USER().
• getTimeDateFunctions(): Returns a comma-separated list of time and date functions supported by the driver. For example, CURDATE(), DAYOFYEAR(date), HOUR(time).

Oracle's JDBC drivers do not support the function keyword, 'fn'. If you try to use this keyword, for example:

{fn concat ("Oracle", "8i") }

Then you will get the error "Non supported SQL92 token at position xx: fn" when you run your Java application. The workaround is to use Oracle SQL syntax.

For example, instead of using the fn keyword in embedded SQL92 syntax:

Statement stmt = conn.createStatement ();
stmt.executeUpdate("UPDATE emp SET ename = {fn CONCAT('My', 'Name')}");

Use Oracle SQL syntax:

stmt.executeUpdate("UPDATE emp SET ename = CONCAT('My', 'Name')");

LIKE Escape Characters

The characters "%" and "_" have special meaning in SQL LIKE clauses (you use "%" to match zero or more characters, "_" to match exactly one character). If you want to interpret these characters literally in strings, you precede them with a special escape character. For example, if you want to use the ampersand "&" as the escape character, you identify it in the SQL statement as {escape '&'}:

Statement stmt = conn.createStatement ();

// Select the empno column from the emp table where the ename starts with '_'
ResultSet rset = stmt.executeQuery
          ("SELECT empno FROM emp WHERE ename LIKE '&_%' {ESCAPE '&'}");

// Iterate through the result and print the employee numbers
while (rset.next ())
   System.out.println (rset.getString (1));

ResultSet rset = stmt.executeQuery("SELECT empno FROM emp
           WHERE ename LIKE '\\_%' {escape '\\'}");

Outer Joins

Oracle's JDBC drivers do not support outer join syntax: {oj outer-join}. The workaround is to use Oracle outer join syntax:

Instead of:

Statement stmt = conn.createStatement ();
ResultSet rset = stmt.executeQuery
     ("SELECT ename, dname 
       FROM {OJ dept LEFT OUTER JOIN emp ON dept.deptno = emp.deptno} 
       ORDER BY ename");

Use Oracle SQL syntax:

Statement stmt = conn.createStatement ();
ResultSet rset = stmt.executeQuery
     ("SELECT ename, dname 
       FROM emp a, dept b WHERE a.deptno = b.deptno(+)
       ORDER BY ename");

Function Call Syntax

Oracle's JDBC drivers support the following procedure and function call syntax:

Procedure calls (without a return value):

{ call procedure_name (argument1, argument2,...) } 

Function calls (with a return value):

{ ? = call procedure_name (argument1, argument2,...) }

SQL92 to SQL Syntax Example

You can write a simple program to translate SQL92 syntax to standard SQL syntax. The following program prints the comparable SQL syntax for SQL92 statements for function calls, date literals, time literals, and timestamp literals. In the program, the oracle.jdbc.OracleSql class parse() method performs the conversions.

import oracle.jdbc.OracleSql; 
 
public class Foo 
{ 
   public static void main (String args[]) throws Exception 
   { 
      show ("{call foo(?, ?)}"); 
      show ("{? = call bar (?, ?)}"); 
      show ("{d '1998-10-22'}"); 
      show ("{t '16:22:34'}"); 
      show ("{ts '1998-10-22 16:22:34'}"); 
   } 
 
   public static void show (String s) throws Exception 
   { 
      System.out.println (s + " => " + new OracleSql().parse (s)); 
   } 
}

The following code is the output that prints the comparable SQL syntax.

{call foo(?, ?)} => BEGIN foo(:1, :2); END; 
{? = call bar (?, ?)} => BEGIN :1 := bar (:2, :3); END; 
{d '1998-10-22'} => TO_DATE ('1998-10-22', 'YYYY-MM-DD') 
{t '16:22:34'} => TO_DATE ('16:22:34', 'HH24:MI:SS') 
{ts '1998-10-22 16:22:34'} => TO_DATE ('1998-10-22 16:22:34', 'YYYY-MM-DD 
HH24:MI:SS') 

Oracle JDBC Notes and Limitations

The following limitations exist in the Oracle JDBC implementation, but all of them are either insignificant or have easy workarounds.

CursorName

Oracle JDBC drivers do not support the get getCursorName() and setCursorName() methods, because there is no convenient way to map them to Oracle constructs. Oracle recommends using ROWID instead. For more information on how to use and manipulate ROWIDs, see "Oracle ROWID Type".

SQL92 Outer Join Escapes

Oracle JDBC drivers do not support SQL92 outer join escapes. Use Oracle SQL syntax with "(+)" instead. For more information on SQL92 syntax, see "Embedded SQL92 Syntax".

PL/SQL TABLE, BOOLEAN, and RECORD Types

It is not feasible for Oracle JDBC drivers to support calling arguments or return values of the PL/SQL RECORD, BOOLEAN, or table with non-scalar element types. However, Oracle JDBC drivers support PL/SQL index-by table of scalar element types. For a complete description of this, see "Accessing PL/SQL Index-by Tables".

As a workaround to PL/SQL RECORD, BOOLEAN, or non-scalar table types, create wrapper procedures that handle the data as types supported by JDBC. For example, to wrap a stored procedure that uses PL/SQL booleans, create a stored procedure that takes a character or number from JDBC and passes it to the original procedure as BOOLEAN or, for an output parameter, accepts a BOOLEAN argument from the original procedure and passes it as a CHAR or NUMBER to JDBC. Similarly, to wrap a stored procedure that uses PL/SQL records, create a stored procedure that handles a record in its individual components (such as CHAR and NUMBER) or in a structured object type. To wrap a stored procedure that uses PL/SQL tables, break the data into components or perhaps use Oracle collection types.

For an example of a workaround for BOOLEAN, see "Boolean Parameters in PL/SQL Stored Procedures".

IEEE 754 Floating Point Compliance

The arithmetic for the Oracle NUMBER type does not comply with the IEEE 754 standard for floating-point arithmetic. Therefore, there can be small disagreements between the results of computations performed by Oracle and the same computations performed by Java.

Oracle stores numbers in a format compatible with decimal arithmetic and guarantees 38 decimal digits of precision. It represents zero, minus infinity, and plus infinity exactly. For each positive number it represents, it represents a negative number of the same absolute value.

It represents every positive number between 10^-30 and (1 - 10^-38) * 10¹²⁶ to full 38-digit precision.

Catalog Arguments to DatabaseMetaData Calls

Certain DatabaseMetaData methods define a catalog parameter. This parameter is one of the selection criteria for the method. Oracle does not have multiple catalogs, but it does have packages. For more information on how the Oracle JDBC drivers treat the catalog argument, see "DatabaseMetaData TABLE_REMARKS Reporting".

SQLWarning Class

The java.sql.SQLWarning class provides information on a database access warning. Warnings typically contain a description of the warning and a code that identifies the warning. Warnings are silently chained to the object whose method caused it to be reported. The Oracle JDBC drivers generally do not support SQLWarning. (As an exception to this, scrollable result set operations do generate SQL warnings, but the SQLWarning instance is created on the client, not in the database.)

For information on how the Oracle JDBC drivers handle errors, see "Processing SQL Exceptions".

Bind by Name

Binding by name is not supported. Under certain circumstances, previous versions of the Oracle JDBC drivers have allowed binding statement variables by name. In the following statement, the named variable EmpId would be bound to the integer 314159.

PreparedStatement p = conn.prepareStatement
                           ("SELECT name FROM emp WHERE id = :EmpId");
p.setInt(1, 314159); 
 

This capability to bind by name is not part of the JDBC specification, either 1.0 or 2.0, and Oracle does not support it. The JDBC drivers can throw a SQLException or produce unexpected results.

Prior releases of the Oracle JDBC drivers did not retain bound values from one call of execute to the next as specified in JDBC 1.0. Bound values are now retained. For example:

PreparedStatement p = conn.prepareStatement
                      ("SELECT name FROM emp WHERE id = :? AND dept = :?");
p.setInt(1, 314159); 
p.setString(2, "SALES"); 
ResultSet r1 = p.execute(); 
p.setInt(1, 425260); 
ResultSet r2 = p.execute();  

Previously, a SQLException would be thrown by the second execute() call because no value was bound to the second argument. In this release, the second execute will return the correct value, retaining the binding of the second argument to the string "SALES".

If the retained bound value is a stream, then the Oracle JDBC drivers will not reset the stream. Unless the application code resets, repositions, or otherwise modifies the stream, the subsequent execute calls will send NULL as the value of the argument.

Related Information

This section lists Web sites that contain useful information for JDBC programmers. Many of the sites are referenced in other sections of this manual. In this list you can find references to the Oracle JDBC drivers, Oracle SQLJ, Java technology, the Java Developer's Kit APIs (for versions 1.2.x and 1.1.x), the Java Security API, and resources to help you write signed applets.

Oracle JDBC Drivers and SQLJ

Oracle JDBC Driver Home Page (Oracle Corporation)

http://www.oracle.com/java/jdbc

Oracle SQLJ Home Page (Oracle Corporation)

http://www.oracle.com/java/sqlj

Java Technology

Java Technology Home Page (Sun Microsystems, Inc.):

http://www.javasoft.com

Java Development Kit (JDK1.2.x and 1.1.x) (Sun Microsystems, Inc.):

http://java.sun.com/products/jdk