9 SQL and PL/SQL Programming in a Global Environment

This chapter contains information useful for SQL programming in a globalization support environment. This chapter includes the following topics:

Locale-Dependent SQL Functions with Optional NLS Parameters

All SQL functions whose behavior depends on globalization support conventions enable NLS parameters to be specified. These functions are:

TO_CHAR
TO_DATE
TO_NUMBER
NLS_UPPER
NLS_LOWER
NLS_INITCAP
NLSSORT

Explicitly specifying the optional NLS parameters for these functions enables the functions to be evaluated independently of the session's NLS parameters. This feature can be important for SQL statements that contain numbers and dates as string literals.

For example, the following query is evaluated correctly if the language specified for dates is AMERICAN:

SELECT last_name FROM employees WHERE hire_date > '01-JAN-1999';

Such a query can be made independent of the current date language by using a statement similar to the following:

SELECT last_name FROM employees
     WHERE hire_date > TO_DATE('01-JAN-1999','DD-MON-YYYY',
     'NLS_DATE_LANGUAGE = AMERICAN');

In this way, SQL statements that are independent of the session language can be defined where necessary. Such statements are necessary when string literals appear in SQL statements in views, CHECK constraints, or triggers.

Note:

Only SQL statements that must be independent of the session NLS parameter values should explicitly specify optional NLS parameters in locale-dependent SQL functions. Using session default values for NLS parameters in SQL functions usually results in better performance.

All character functions support both single-byte and multibyte characters. Except where explicitly stated, character functions operate character by character, rather than byte by byte.

The rest of this section includes the following topics:

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.

Table 9-1 SQL Functions and Their Valid NLS Parameters

SQL Function Valid NLS Parameters

TO_DATE

NLS_DATE_LANGUAGE NLS_CALENDAR

TO_NUMBER

NLS_NUMERIC_CHARACTERS NLS_CURRENCY NLS_DUAL_CURRENCY NLS_ISO_CURRENCY

TO_CHAR

NLS_DATE_LANGUAGE NLS_NUMERIC_CHARACTERS NLS_CURRENCY NLS_ISO_CURRENCY NLS_DUAL_CURRENCY NLS_CALENDAR

TO_NCHAR

NLS_DATE_LANGUAGE NLS_NUMERIC_CHARACTERS NLS_CURRENCY NLS_ISO_CURRENCY NLS_DUAL_CURRENCY NLS_CALENDAR

NLS_UPPER

NLS_SORT

NLS_LOWER

NLS_SORT

NLS_INITCAP

NLS_SORT

NLSSORT

NLS_SORT


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')

Note:

In some languages, some lowercase characters correspond to more than one uppercase character or vice versa. As a result, the length of the output from the NLS_UPPER, NLS_LOWER, and NLS_INITCAP functions can differ from the length of the input.

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.

Other Locale-Dependent SQL Functions

This section includes the following topics:

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.

See Also:

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.

Table 9-2 How the SUBSTR Functions Calculate the Length of a String

Function Calculation Method

SUBSTR

Calculates the length of a string in characters based on the length semantics associated with the character set of the datatype. For example, AL32UTF8 characters are calculated in UCS-4 characters. UTF8 and AL16UTF16 characters are calculated in UCS-2 characters. A supplementary character is counted as one character in AL32UTF8 and as two characters in UTF8 and AL16UTF16. Because VARCHAR and NVARCHAR may use different character sets, SUBSTR may give different results for different datatypes even if two strings are identical. If your application requires consistency, then use SUBSTR2 or SUBSTR4 to force all semantic calculations to be UCS-2 or UCS-4, respectively.

SUBSTRB

Calculates the length of a string in bytes.

SUBSTR2

Calculates the length of a string in UCS-2 characters, which is compliant with Java strings and Windows client environments. Characters are represented in UCS-2 or 16-bit Unicode values. Supplementary characters are counted as two characters.

SUBSTR4

Calculates the length of a string in UCS-4 characters. Characters are represented in UCS-4 or 32-bit Unicode values. Supplementary characters are counted as one character.

SUBSTRC

Calculates the length of a string in Unicode composed characters. Supplementary characters and composed characters are counted as one character.


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

See Also:

Oracle Database SQL Reference for more information about the SUBSTR, LENGTH, and INSTR functions

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.

Table 9-3 LIKE Conditions

Function Description

LIKE2

Use when characters are represented in UCS-2 semantics. A supplementary character is considered as two characters.

LIKE4

Use when characters are represented in UCS-4 semantics. A supplementary character is considered as one character.

LIKEC

Use when characters are represented in Unicode complete character semantics. A composed character is treated as one character.


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

The NLS_CHARSET_NAME(n) function returns the name of the character set corresponding to ID number n. The function returns NULL if n is not a recognized character set ID value.

Converting from Character Set Name to Character Set Number

NLS_CHARSET_ID(text) returns the character set ID corresponding to the name specified by text. text is defined as a run-time VARCHAR2 quantity, a character set name. Values for text can be NLSRTL names that resolve to character sets that are not the database character set or the national character set.

If the value CHAR_CS is entered for text, then the function returns the ID of the database character set. If the value NCHAR_CS is entered for text, then the function returns the ID of the database's national character set. The function returns NULL if text is not a recognized name.

Note:

The value for text must be entered in uppercase characters.

Returning the Length of an NCHAR Column

NLS_CHARSET_DECL_LEN(BYTECNT, CSID) returns the declaration length of a column in number of characters, given the byte length of the column. BYTECNT is the byte length of the column. CSID is the character set ID of the column.

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.

Example 9-1 Specifying a German Sort with the NLS_SORT Session Parameter

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

Example 9-2 Specifying a French Sort with the NLSSORT Function

This example first sets the NLS_SORT session parameter to German, but the NLSSORT function overrides it by specifying a French sort.

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

The WHERE clause uses binary comparison when NLS_COMP is set to BINARY, but this can be overridden by using the NLSSORT function in the WHERE clause.

Example 9-3 Making a Linguistic Comparison with the WHERE Clause

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

Setting the NLS_COMP session parameter to LINGUISTIC causes the NLS_SORT value to be used in the WHERE clause.

The rest of this section contains the following topics:

NLSSORT Syntax

There are four ways to use NLSSORT:

  • NLSSORT(), which relies on the NLS_SORT parameter

  • NLSSORT(column1, 'NLS_SORT=xxxx')

  • NLSSORT(column1, 'NLS_LANG=xxxx')

  • NLSSORT(column1, 'NLS_LANGUAGE=xxxx')

The NLS_LANG parameter of the NLSSORT function is not the same as the NLS_LANG client environment setting. In the NLSSORT function, NLS_LANG specifies the abbreviated language name, such as US for American or PL for Polish. For example:

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

Comparing Strings in a WHERE Clause

NLSSORT enables applications to perform string matching that follows alphabetic conventions. Normally, character strings in a WHERE clause are compared by using the binary values of the characters. One character is considered greater than another character if it has a greater binary value in the database character set. Because the sequence of characters based on their binary values might not match the alphabetic sequence for a language, such comparisons may not follow alphabetic conventions. For example, if a column (column1) contains the values ABC, ABZ, BCD, and ÄBC in the ISO 8859-1 8-bit character set, then the following query returns both BCD and ÄBC because Ä has a higher numeric value than B:

SELECT column1 FROM table1 WHERE column1 > 'B';

In German, Ä is sorted alphabetically before B, but in Swedish, Ä is sorted after Z. Linguistic comparisons can be made by using NLSSORT in the WHERE clause:

WHERE NLSSORT(col) comparison_operator NLSSORT(comparison_string)

Note that NLSSORT must be on both sides of the comparison operator. For example:

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

If a German linguistic sort has been set, then the statement does not return strings beginning with Ä because Ä comes before B in the German alphabet. If a Swedish linguistic sort has been set, then strings beginning with Ä are returned because Ä comes after Z in the Swedish alphabet.

Using the NLS_COMP Parameter to Simplify Comparisons in the WHERE Clause

Comparison in the WHERE clause or PL/SQL blocks is binary by default. Using the NLSSORT function for linguistic comparison can be tedious, especially when the linguistic sort has already been specified in the NLS_SORT session parameter. You can use the NLS_COMP parameter to indicate that the comparisons in a WHERE clause or in PL/SQL blocks must be linguistic according to the NLS_SORT session parameter.

Note:

The NLS_COMP parameter does not affect comparison behavior for partitioned tables. String comparisons that are based on a VALUES LESS THAN partition are always binary.

See Also:

"NLS_COMP"

Controlling an ORDER BY Clause

If a linguistic sort is in use, then ORDER BY clauses use an implicit NLSSORT on character data. The sort mechanism (linguistic or binary) for an ORDER BY clause is transparent to the application. However, if the NLSSORT function is explicitly specified in an ORDER BY clause, then the implicit NLSSORT is not done.

If a linguistic sort has been defined by the NLS_SORT session parameter, then an ORDER BY clause in an application uses an implicit NLSSORT function. If you specify an explicit NLSSORT function, then it overrides the implicit NLSSORT function.

When the sort mechanism has been defined as linguistic, the NLSSORT function is usually unnecessary in an ORDER BY clause.

When the sort mechanism either defaults or is defined as binary, then a query like the following uses a binary sort:

SELECT last_name FROM employees 
     ORDER BY last_name;

A German linguistic sort can be obtained as follows:

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

Miscellaneous Topics for SQL and PL/SQL Programming in a Global Environment

This section contains the following topics:

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 2007, DD-rm-YYYY returns 07-ix-2007 and DD-RM-YYYY returns 07-IX-2007.

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 2007 is in ISO week number 53 of 2008. 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:

Element Description Purpose
D Decimal Returns the decimal point character
G Group Returns the group separator
L Local currency Returns the local currency symbol
C International currency Returns the ISO currency symbol
RN Roman numeral Returns the number as its Roman numeral equivalent

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. Oracle Database performs character set conversion before loading the binary data into CLOB or NCLOB columns. Thus, the BFILE data does not need to be in the same character set as the database or national character set to work properly. 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.