9 SQL and PL/SQL Programming in a Global Environment

Default Values for NLS Parameters in SQL Functions

When SQL functions evaluate views and triggers, default values from the current session are used for the NLS function parameters. When SQL functions evaluate CHECK constraints, they use the default values that were specified for the NLS parameters when the database was created.

Specifying NLS Parameters in SQL Functions

NLS parameters are specified in SQL functions as follows:

'parameter = value'

For example:

'NLS_DATE_LANGUAGE = AMERICAN'

The following NLS parameters can be specified in SQL functions:

NLS_DATE_LANGUAGE

NLS_NUMERIC_CHARACTERS

NLS_CURRENCY

NLS_ISO_CURRENCY

NLS_DUAL_CURRENCY

NLS_CALENDAR

NLS_SORT

Table 9-1 shows which NLS parameters are valid for specific SQL functions.

The following examples show how to use NLS parameters in SQL functions:

TO_DATE ('1-JAN-99', 'DD-MON-YY',
   'nls_date_language = American')

TO_CHAR (hire_date, 'DD/MON/YYYY',
   'nls_date_language = French')

TO_CHAR (SYSDATE, 'DD/MON/YYYY',
    'nls_date_language=''Traditional Chinese'' ')

TO_NUMBER ('13.000,00', '99G999D99',
   'nls_numeric_characters = '',.''')

TO_CHAR (salary, '9G999D99L', 'nls_numeric_characters = '',.''
   nls_currency = ''EUR''')

TO_CHAR (salary, '9G999D99C', 'nls_numeric_characters = ''.,''
   nls_iso_currency = Japan')

NLS_UPPER (last_name, 'nls_sort = Swiss')

NLSSORT (last_name, 'nls_sort = German')

Unacceptable NLS Parameters in SQL Functions

The following NLS parameters are not accepted in SQL functions except for NLSSORT:

• NLS_LANGUAGE

• NLS_TERRITORY

• NLS_DATE_FORMAT

NLS_DATE_FORMAT and NLS_TERRITORY_FORMAT are not accepted as parameters because they can interfere with required format masks. A date format must always be specified if an NLS parameter is in a TO_CHAR or TO_DATE function. As a result, NLS_DATE_FORMAT and NLS_TERRITORY_FORMAT are not valid NLS parameters for the TO_CHAR or TO_DATE functions. If you specify NLS_DATE_FORMAT or NLS_TERRITORY_FORMAT in the TO_CHAR or TO_DATE function, then an error is returned.

NLS_LANGUAGE can interfere with the session value of NLS_DATE_LANGUAGE. If you specify NLS_LANGUAGE in the TO_CHAR function, for example, then its value is ignored if it differs from the session value of NLS_DATE_LANGUAGE.

The CONVERT Function

The CONVERT function enables conversion of character data between character sets.

The CONVERT function converts the binary representation of a character string in one character set to another. It uses exactly the same technique as conversion between database and client character sets. Hence, it uses replacement characters and has the same limitations.

The syntax for CONVERT is as follows:

CONVERT(char, dest_char_set[, source_char_set])

char is the value to be converted. source_char_set is the source character set and dest_char_set is the destination character set. If the source_char_set parameter is not specified, then it defaults to the database character set.

SQL Functions for Different Length Semantics

Oracle provides SQL functions that work in accordance with different length semantics. There are three groups of such SQL functions: SUBSTR, LENGTH, and INSTR. Each function in a group is based on a different kind of length semantics and is distinguished by the character or number appended to the function name. For example, SUBSTRB is based on byte semantics.

The SUBSTR functions return a requested portion of a substring. The LENGTH functions return the length of a string. The INSTR functions search for a substring in a string.

The SUBSTR functions calculate the length of a string differently. Table 9-2 summarizes the calculation methods.

The LENGTH and INSTR functions calculate string length in the same way, according to the character or number added to the function name.

The following examples demonstrate the differences between SUBSTR and SUBSTRB on a database whose character set is AL32UTF8.

For the string Fußball, the following statement returns a substring that is 4 characters long, beginning with the second character:

SELECT SUBSTR ('Fußball', 2 , 4) SUBSTR FROM DUAL;

SUBS
----
ußba

For the string Fußball, the following statement returns a substring 4 bytes long, beginning with the second byte:

SELECT SUBSTRB ('Fußball', 2 , 4) SUBSTRB FROM DUAL;

SUB
---
ußb

LIKE Conditions for Different Length Semantics

The LIKE conditions specify a test that uses pattern-matching. The equality operator (=) exactly matches one character value to another, but the LIKE conditions match a portion of one character value to another by searching the first value for the pattern specified by the second.

LIKE calculates the length of strings in characters using the length semantics associated with the input character set. The LIKE2, LIKE4, and LIKEC conditions are summarized in Table 9-3.

There is no LIKEB condition.

Character Set SQL Functions

Two SQL functions, NLS_CHARSET_NAME and NLS_CHARSET_ID, can convert between character set ID numbers and character set names. They are used by programs that need to determine character set ID numbers for binding variables through OCI.

Another SQL function, NLS_CHARSET_DECL_LEN, returns the declaration length of a column in number of characters, given the byte length of the column.

This section includes the following topics:

• Converting from Character Set Number to Character Set Name

• Converting from Character Set Name to Character Set Number

• Returning the Length of an NCHAR Column

  See Also:

  Oracle Database SQL Reference

The NLSSORT Function

The NLSSORT function enables you to use any linguistic sort for an ORDER BY clause. It replaces a character string with the equivalent sort string used by the linguistic sort mechanism so that sorting the replacement strings produces the desired sorting sequence. For a binary sort, the sort string is the same as the input string.

The kind of linguistic sort used by an ORDER BY clause is determined by the NLS_SORT session parameter, but it can be overridden by explicitly using the NLSSORT function.

Example 9-1 specifies a German sort with the NLS_SORT session parameter.

ALTER SESSION SET NLS_SORT = GERMAN;
SELECT * FROM table1
     ORDER BY column1;

ALTER SESSION SET NLS_SORT = GERMAN;
SELECT * FROM table1
     ORDER BY NLSSORT(column1, 'NLS_SORT=FRENCH');

ALTER SESSION SET NLS_COMP = BINARY;
SELECT * FROM table1
WHERE NLSSORT(column1, 'NLS_SORT=FRENCH')>
      NLSSORT(column2, 'NLS_SORT=FRENCH');

• NLSSORT Syntax

• Comparing Strings in a WHERE Clause

• Using the NLS_COMP Parameter to Simplify Comparisons in the WHERE Clause

• Controlling an ORDER BY Clause

SELECT * FROM table1
ORDER BY NLSSORT(column1, 'NLS_LANG=PL');

SELECT column1 FROM table1 WHERE column1 > 'B';

WHERE NLSSORT(col) comparison_operator NLSSORT(comparison_string)

SELECT column1 FROM table1 WHERE NLSSORT(column1) > NLSSORT('B');

SELECT last_name FROM employees 
     ORDER BY last_name;

SELECT last_name FROM employees
     ORDER BY NLSSORT(last_name, 'NLS_SORT = GERMAN');

SQL Date Format Masks

Several format masks are provided with the TO_CHAR, TO_DATE, and TO_NUMBER functions.

The RM (Roman Month) format element returns a month as a Roman numeral. You can specify either upper case or lower case by using RM or rm. For example, for the date 7 Sep 1998, DD-rm-YYYY returns 07-ix-1998 and DD-RM-YYYY returns 07-IX-1998.

Note that the MON and DY format masks explicitly support month and day abbreviations that may not be three characters in length. For example, the abbreviations "Lu" and "Ma" can be specified for the French "Lundi" and "Mardi", respectively.

Calculating Week Numbers

The week numbers returned by the WW format mask are calculated according to the following algorithm: int(dayOfYear+6)/7. This algorithm does not follow the ISO standard (2015, 1992-06-15).

To support the ISO standard, the IW format element is provided. It returns the ISO week number. In addition, the I, IY, IYY, and IYYY format elements, equivalent in behavior to the Y, YY, YYY, and YYYY format elements, return the year relating to the ISO week number.

In the ISO standard, the year relating to an ISO week number can be different from the calendar year. For example, 1st Jan 1988 is in ISO week number 53 of 1987. A week always starts on a Monday and ends on a Sunday. The week number is determined according the following rules:

• If January 1 falls on a Friday, Saturday, or Sunday, then the week including January 1 is the last week of the previous year, because most of the days in the week belong to the previous year.

• If January 1 falls on a Monday, Tuesday, Wednesday, or Thursday, then the week is the first week of the new year, because most of the days in the week belong to the new year.

For example, January 1, 1991, is a Tuesday, so Monday, December 31, 1990, to Sunday, January 6, 1991, is in week 1. Thus, the ISO week number and year for December 31, 1990, is 1, 1991. To get the ISO week number, use the IW format mask for the week number and one of the IY formats for the year.

SQL Numeric Format Masks

Several additional format elements are provided for formatting numbers:

For Roman numerals, you can specify either upper case or lower case, using RN or rn, respectively. The number being converted must be an integer in the range 1 to 3999.

Loading External BFILE Data into LOB Columns

The DBMS_LOB PL/SQL package can load external BFILE data into LOB columns. Previous releases of Oracle did not perform character set conversion before loading the binary data into CLOB or NCLOB columns. Thus the BFILE data had to be in the same character set as the database or national character set to work properly. The APIs that were introduced in Oracle9i Release 2 (9.2) allow the user to specify the character set ID of the BFILE data by using a new parameter. The APIs convert the data from the specified BFILE character set into the database character set for the CLOB datatype or the national character set for the NCLOB datatype. The loading takes place on the server because BFILE data is not supported on the client.

• Use DBMS_LOB.LOADBLOBFROMFILE to load BLOB columns.

• Use DBMS_LOB.LOADCLOBFROMFILE to load CLOB and NCLOB columns.

  See Also:

  • PL/SQL Packages and Types Reference

  • Oracle Database Application Developer's Guide - Large Objects