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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
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.
LAST_DAY Function
The LAST_DAY function requires a DATE or DATETIME expression as its only argument. It returns the date of the last day of the month that its argument specifies.

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.
        ADD_MONTHS Function
        The ADD_MONTHS function takes a DATETIME or DATE expression as its first argument, and requires a second integer argument, specifying the number of months to add to the first argument value. The second argument can be positive or negative.
        DATE Function
        The DATE function converts its argument to a DATE value.
        DAY Function
        The DAY function takes a DATE or DATETIME argument and returns the day of the month as an integer in the range from 1 to the number of days in the current month.
        MONTH Function
        The MONTH function returns an integer corresponding to the month portion of its DATE or DATETIME argument.
        QUARTER Function
        The QUARTER function returns an integer in the range 1 through 4 that corresponds to the quarter of the calendar year that includes its DATE or DATETIME argument.
        WEEKDAY Function
        The WEEKDAY function accepts a DATE or DATETIME argument, and returns an integer in the range from 0 to 6 that represents the day of the week.
        YEAR Function
        The YEAR function takes a DATE or DATETIME argument and returns a four-digit integer that represents the year.
        MONTHS_BETWEEN Function
        The MONTHS_BETWEEN function accepts two DATE or DATETIME expressions as arguments, and returns a signed DECIMAL value that quantifies the interval between those arguments in months, as if month were a unit of time.
        LAST_DAY Function
        The LAST_DAY function requires a DATE or DATETIME expression as its only argument. It returns the date of the last day of the month that its argument specifies.
        NEXT_DAY Function
        The NEXT_DAY function returns the earliest date that is later than its DATE or DATETIME first argument, and that falls on the day of the week that its second argument specifies. This second argument is a quoted string of three ASCII characters that abbreviates the English name of the day of the week.
        EXTEND Function
        The EXTEND function adjusts the precision of a DATETIME or DATE value.
        MDY Function
        The MDY function takes as its arguments three integer expressions that represent the month, day, and year, and returns a type DATE value.
        TO_CHAR Function
        The TO_CHAR function converts an expression that evaluates to a DATE, DATETIME, or numeric value to a character string.
        TO_DATE Function
        The TO_DATE function converts a character string to a DATETIME value. The function evaluates the char_expression first argument as a date, according to the date format that the format_string second argument specifies, and returns the equivalent date.
        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.
        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.

LAST_DAY Function

The LAST_DAY function requires a DATE or DATETIME expression as its only argument. It returns the date of the last day of the month that its argument specifies.

The data type of this returned value is the same data type as the argument. The difference between the returned value and the argument is the number of days remaining in that month.

The following query returns the DATE representation of the current date, the date of the last day in the current month, and the integer number of days (calculated by subtracting the first DATE value from second) before the last day in the current month:

SELECT TODAY AS today, LAST_DAY(TODAY) AS last,
   LAST_DAY(TODAY) - TODAY AS days_left 
   FROM systables WHERE tabid = 1;

If the query were issued on 12 March 2018, with MDY4/ as the DBDATE setting for the default locale, it would return the following information:

today      last         days_left

03/12/2018 03/31/2018          19

In the SELECT statement of this example, there is no name conflict in the Projection clause between the TODAY operator and the identifier today, because the AS keyword indicates to Informix® that today is a display label.

If you use a host variable to store the argument to LAST_DAY, but the data type of the argument is not known at prepare time, Informix® assumes that the data type is DATETIME YEAR TO FRACTION(5). If at runtime, after the statement has been prepared, the user supplies a DATE value for the host variable, error -9750 is issued. To prevent this error, specify the data type of the host variable by using a cast, as in this program fragment:

sprintf(query, , 
   select last_day(?::date) from mytab);
EXEC SQL prepare selectq from :query;
EXEC SQL declare select_cursor cursor for selectq;
EXEC SQL open select_cursor using :hostvar_date_input;
	
EXEC SQL fetch select_cursor into :var_date_output;