String delimiters

Informix®

The ANSI SQL string delimiter character is the single quote ('string'), while double quotes are used to delimit database object names:

SELECT ... WHERE "tabname"."colname" = 'a string value'

In Informix databases created in native mode (non-ANSI), you can use double quotes as string delimiters:

SELECT ... WHERE tabname.colname = 'a string value'

This is important, since many BDL programs use that character to delimit the strings in SQL commands.

Note: This problem concerns only double quotes within SQL statements. Double quotes used in pure BDL string expressions are not subject to SQL compatibility problems.

Microsoft™ SQL Server

Microsoft SQL Server follows the ANSI SQL specification, using single quotes for string delimiters and double quotes for database object names.

Important:

With SQL Server, all UNICODE strings must be prefaced with an N character:

UPDATE cust SET cust_name = N'矇閬頝' WHERE cust_id=123

Without the N prefix, SQL Server will convert the characters from the current system locale to the database locale. With the N prefix, the server can recognize a UNICODE string and use it as is to insert into NCHAR or NVARCHAR columns.

Solution

When using Static SQL statements, the fglcomp compiler converts string literals using double quotes to string literals with single quotes:

$ cat s.4gl
MAIN
   DEFINE n INT
   SELECT COUNT(*) INTO n FROM tab1 WHERE col1 = "abc"
END MAIN

$ fglcomp -S s.4gl
s.4gl^3^SELECT COUNT(*) FROM tab1 WHERE col1 = 'abc'

However, SQL statements created dynamically are not modified by the Genero compiler.

The Genero database interface can automatically replace all double quotes by single quotes in SQL statements. This applies to static and dynamic SQL statements.

The The translation of double quoted expression to single quoted expressions can be controlled with the following FGLPROFILE entry:

dbi.database.dbname.ifxemul.dblquotes = { true | false }

For more details see IBM Informix emulation parameters in FGLPROFILE.

However, database object names must not be delimited by double quotes, because the database interface cannot determine the difference between a database object name and a quoted string ! For example, if the program executes the SQL statement:

... WHERE "tabname"."colname" = "a string value"

replacing all double quotes by single quotes would produce:

... WHERE 'tabname'.'colname' = 'a string value'

This would produce an error since 'tabname'.'colname' is not allowed by ORACLE.

Escaped string delimiters can be used inside strings like the following:

'This is a single quote: '''
'This is a single quote: \''
"This is a double quote: """
"This is a double quote: \""

Although double quotes are replaced automatically in SQL statements, it is recommended that you use only single quotes to enforce portability.

National character strings

When using the SNC database driver, all string literals of an SQL statement are automatically changed to get the N prefix. Thus, you don't need to add the N prefix by hand in all of your programs. This solution makes by the way your Genero code portable to other databases.

With the SNC database driver, character string data is converted from the current Genero BDL locale to Wide Char (Unicode UCS-2), before is it used in an ODBC call such as SQLPrepareW or SQLBindParameter(SQL_C_WCHAR). When fetching character data, the SNC database driver converts from Wide Char to the current Genero BDL locale. The current Genero BDL locale is defined by LANG, and if LANG is not defined, the default is the ANSI Code Page of the Windows™ operating system. See CHARACTER data types for more details.

When using the FTM (FreeTDS) or the ESM (Easysoft) database driver on UNIX™, string literals get the N prefix if the current locale is a multibyte encoding like BIG5, EUC-JP or UTF-8. If the current locale is a single-byte encoding like ISO-8859-1, no prefix will be added to the string literals.