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SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
Guide to SQL: Syntax
The Informix® Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the Informix dialect of the SQL language.
Data types and expressions
These topics describe the data types and expressions that Informix®supports.
Expression
Function Expressions
Substring functions
The built-in SQL substring functions return substrings from character string arguments, or return positional information for operations on substrings.
LEFT function
The LEFT function returns a substring consisting of the leftmost N characters from a string argument.

SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
- Guide to SQL: Syntax
  The Informix® Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the Informix dialect of the SQL language.
  - Overview of SQL syntax
    These topics provide an overview about how to use the SQL statements, SPL statements, and syntax segments.
  - SQL statements
    This chapter describes the syntax and semantics of SQL statements that are recognized by Informix®.
  - SPL statements
    These topics describe Stored Procedure Language (SPL) statements, which you use to write SPL routines. You can store these routines in the database as user-defined routines (UDRs).
  - Data types and expressions
    These topics describe the data types and expressions that Informix®supports.
    - Scope of Segment Descriptions
    - Use of Segment Descriptions
    - Data type and expression segments
      Data type and expression segments can appear in SQL statements.
    - Collection Subquery
    - Condition
    - Data Type
      The Data Type segment specifies the data type of a column, of a component of a collection, of a field within a ROW type, of a routine parameter, or of a value returned by an expression or by a cast function. Use this segment whenever you see a reference to a data type in a syntax diagram.
    - DATETIME Field Qualifier
      Use a DATETIME Field Qualifier to specify the largest and smallest unit of time in a DATETIME column or value. Use this segment whenever you see a reference to a DATETIME Field Qualifier in a syntax diagram.
    - Expression
      - List of Expressions
        Each category of SQL expression includes many individual expressions.
      - Arithmetic Operators
      - Bitwise Logical Functions
      - Concatenation Operator
      - CAST Expressions
        Use the CAST (... AS ...) keywords or the double-colon ( :: ) cast operator to convert the data type of the value of an expression to some other target data type.
      - Column Expressions
        A column expression specifies a data value in a column in the database, or a substring of the value, or a field within a ROW-type column, or a field in a BSON column.
      - Conditional Expressions
      - Constant Expressions
        Certain expressions that return a fixed value are called constant expressions. These include variant function operators that read the system clock, but that are valid in contexts where literal constants are also valid.
      - Constructor Expressions
      - NULL Keyword
      - Function Expressions
        Algebraic Functions
        Bitshift Functions
        Bitshift functions perform a bit shift operation on an integer or bigint value and return the shift result.
        CARDINALITY Function
        The CARDINALITY function returns the number of elements in a collection column (SET, MULTISET, LIST).
        SQLCODE Function (SPL)
        The SQLCODE function takes no arguments, but returns to its calling context the value of sqlca.sqlcode for the most recently executed SQL statement (whether static or dynamic) that the current SPL routine has executed. Only use SQLCODE in the context of a cursor.
        DBINFO Function
        Encryption and decryption functions
        Informix® supports built-in encryption and decryption functions.
        DECRYPT_CHAR Function
        DECRYPT_BINARY Function
        ENCRYPT_AES Function
        ENCRYPT_TDES Function
        GETHINT Function
        Exponential and Logarithmic Functions
        Exponential and logarithmic functions take at least one argument and return a FLOAT data type.
        NVL2 Function
        Returns the second argument when the first argument is not NULL. If the first argument is NULL, the third argument is returned.
        HEX Function
        Length functions
        Use length functions to determine the length of a character column, string, or variable, or of the value returned by a character expression, or (for CHAR_LENGTH in multibyte locales) the number of logical characters.
        Security Label Support Functions
        SIGN function
        The SIGN function returns an indicator of the sign of the argument.
        Smart-Large-Object Functions
        The smart-large-object functions support objects of BLOB and CLOB data types:
        Time Functions
        The time functions of Informix® accept DATE or DATETIME arguments, or character representation of a DATE or DATETIME value. They typically return DATE or DATETIME values, or convert information that they extract from DATE or DATETIME values into character strings or integers.
        TO_NUMBER Function
        The TO_NUMBER function can convert a number or a character expression representing a number value to a DECIMAL data type.
        Trigonometric Functions
        The built-in trigonometric functions calculate ratios of the lengths of the sides of right triangles. Two supporting functions, DEGREES and RADIANS, can respectively convert the units of angular values from radians to degrees, and from degrees to radians.
        String-Manipulation Functions
        String-manipulation functions perform various operations on strings of characters.
        Case-Conversion Functions
        The case-conversion functions perform lettercase conversion on alphabetic characters. In the default locale, only the ASCII characters in the ranges A - Z and a - z can be modified by these functions, which enable you to perform case-insensitive searches in your queries and to specify the format of the output.
        Substring functions
        The built-in SQL substring functions return substrings from character string arguments, or return positional information for operations on substrings.
        CHARINDEX function
        The CHARINDEX function searches a character string for the first occurrence of a target substring, where the search begins at a specified or default character position within the source string.
        INSTR function
        The INSTR function searches a character string for a specified substring, and returns the character position in that string where an occurrence of that a substring ends, based on a count of substring occurrences.
        LEFT function
        The LEFT function returns a substring consisting of the leftmost N characters from a string argument.
        RIGHT function
        The RIGHT function returns a substring consisting of the rightmost N characters from a string argument.
        SUBSTR function
        SUBSTRB function
        Returns a substring of a string, beginning at a specified position in the string.
        SUBSTRING function
        SUBSTRING_INDEX function
        The SUBSTRING_INDEX function searches a character string for a specified delimiter character, and returns a substring of the leading or trailing characters, based on a count of a delimiter that you specify as an argument to the function.
        FORMAT_UNITS Function
        The FORMAT_UNITS function can interpret strings that specify a number and the abbreviated names of units of memory or of mass storage.
        IFX_ALLOW_NEWLINE Function
        The IFX_ALLOW_NEWLINE function sets a newline mode that allows newline characters in quoted strings or disallows newline characters in quoted strings within the current session.
        User-Defined Functions
        A user-defined function (UDF) is a routine that you write in SPL or in a language external to the database, such as C or Java™, and that returns a value to its calling context.
      - Statement-Local Variable Expressions
      - Aggregate Expressions
    - OLAP window expressions
      You can include On-Line Analytical Processing (OLAP) expressions in a SELECT statement to operate on subsets of the rows in the result set of a query or subquery. You can use OLAP window expressions to examine subsets of the qualifying rows for patterns, trends, or exceptions in the data.
    - INTERVAL Field Qualifier
    - Literal Collection
    - Literal DATETIME
      The Literal DATETIME segment specifies a DATETIME value
    - Literal INTERVAL
      The Literal INTERVAL segment specifies a literal INTERVAL value. Use this whenever you see a reference to a literal INTERVAL in a syntax diagram.
    - Literal Number
    - Literal Row
      The Literal Row segment specifies the syntax for literal values of named and unnamed ROW data types.
    - Quoted String
    - Relational Operator
  - Other syntax segments
    These topics describe syntax segments, which are language elements, such as database object names or optimizer directives, that appear as a subdiagram reference in the syntax diagrams of some SQL or SPL statements.
  - Built-In Routines
  - Appendixes
- Guide to SQL: Reference
  The Informix® Guide to SQL: Reference contains the reference information for the system catalog tables, data types, and environment variables of the HCL Informix dialect of the SQL language, as implemented in HCL Informix. These topics also include information about the stores_demo, sales_demo, and superstore_demo databases that are included with HCL Informix.
- Guide to SQL: Tutorial
  The Informix® Guide to SQL: Tutorial shows how to use basic and advanced structured query language (SQL) to access and manipulate the data in your databases. It discusses the data manipulation language (DML) statements as well as triggers and stored procedure language (SPL) routines, which DML statements often use.

LEFT function

The LEFT function returns a substring consisting of the leftmost N characters from a string argument.

The function has this syntax:

LEFT function

LEFT(source_string, position)


Element	Description	Restrictions	Syntax
position	Ordinal position (from the left) in the string; this character and all to the left are to be returned	Must be an expression, constant, column, or host variable of a built-in integer type, or that can be converted to an integer	Expression
source_string	Expression that evaluates to a character string	Must be an expression, constant, column, or host variable of a data type that can be converted to a character type	Expression

The arguments to the LEFT function cannot be user-defined data types.

What the LEFT function returns depends on the number of logical characters in source_string and on the value of position:

If source_string evaluates to a string with more than position characters, the return value is a substring of source_string, consisting of all characters to the left of the specified position.
If source_string evaluates to a string with no more than position characters, the return value is the entire source_string.
If source_string evaluates to NULL, or if position is zero or negative, then NULL is returned.
If no position argument is specified, no string value is returned, and an exception is issued.

The return data type is the same as its source_string argument. If a host variable is the source, the return value is either NVARCHAR or NCHAR, according to the length of the returned string, using the return type promotion rules that the section Return Types from the CONCAT Function describes.

The following function expression requests the first five characters of a quoted string:

 LEFT('www.ibm.com',5)

In this example, the LEFT function returns the substring www.i