HPlogo ALLBASE/SQL Reference Manual: HP 3000 MPE/iX Computer Systems > Chapter 8 Expressions

CAST Function
» 

Technical documentation

Complete book in PDF
» Feedback

 » Table of Contents

 » Index

spacerspacerspacer
spacer
spacer
  		 
 

The CAST function converts data from one data type to another. The CAST function can be used anywhere a general expression is allowed. CAST is supported inside functions that support expressions including aggregate functions. CAST also takes general expressions including nested functions as input.

Scope

SQL Data Manipulation Statements

SQL Syntax

{CAST ({ Expression NULL } { AS , }DataType [,FormatSpec])}

Parameters

Expression

is the value to be converted. See the "Expression" section in this chapter for details on the syntax.

DataType

ALLBASE/SQL data type: CHAR(n), VARCHAR(n), DECIMAL(p[,s]), FLOAT, REAL, INTEGER, SMALLINT, DATE, TIME, DATETIME, INTERVAL, BINARY(n), VARBINARY(n), TID.

The LONG BINARY(n) and LONG VARBINARY(n) cannot be used in the CAST operations.

FormatSpec

Format specification used for DATE, TIME, DATETIME, INTERVAL conversions. FormatSpec is the same as that used in the date/time conversion functions.

Description

The following table shows what data type conversions the CAST function supports. These are the status codes used in the table:

  • Y—is supported

  • N—is not supported

  • E—is an ALLBASE/SQL Extension (not a part of ANSI standard)

Table 8-1 Data Types for CAST Function

Source

Data Type

Target Data Type          
EN [1]AN[2]VCCHAR(n)BVBDATETIMEDTITID
EN[1]Y[3]Y[3]Y[4]Y[4]E[4]E[4]NNNNN
AN[2]Y[3]Y[3]Y[4]Y[4]E[4]E[4]NNNNN
VARCHAR(n)Y[4]Y[4]Y[3]Y[3]Y[3]Y[3]Y[3]Y[3]Y[3]Y[3]E[4]
CHAR(n)Y[4]Y[4]Y[3]Y[3]Y[3]Y[3]Y[3]Y[3]Y[3]Y[3]E[4]
BINARYE[4]E[4]Y[3]Y[3]Y[3]Y[3]E[4]E[4]E[4]E[4]E[4]
VARBINARY(n)E[4]E[4]Y[3]Y[3]Y[3]Y[3]E[4]E[4]E[4]E[4]E[4]
DATEE[3]E[3]Y[3]Y[3]E[4]E[4]Y[3]NNNN
TIMEE[3]E[3]Y[3]Y[3]E[4]E[4]NY[3]NNN
DATETIMEE[3]E[3]Y[3]Y[3]E[4]E[4]NNY[3]NN
INTERVALY[3]E[3]Y[3]Y[3]E[4]E[4]NNNY[3]N
TIDNNE[4]E[4]E[4]E[4]NNNNY[3]

[1] EN—Exact Numeric (SMALLINT, INT[EGER], DEC[IMAL][(p[,s])], NUMERIC[(p[,s])])

[2] AN—Approximate Numeric (FLOAT[(p)] or DOUBLE PRECISION, REAL)

[3] Implicit conversion also supported

[4] Conversion supported only with CAST

 

  • If input to CAST is NULL, then the result of the CAST operation is NULL.

  • ALLBASE/SQL supports implicit data conversion between:

    • Numeric data types to numeric data types

    • Character data types to character data types

    • Binary data types to binary data types

    • Binary data types to character data types

    • Character data types to binary data types

    When CAST is used to do these conversions, all existing rules are applied.

  • When a number is converted, if the number does not fit within the target precision, an overflow error occurs.

  • When converting from an approximate numeric to an exact numeric or from an exact numeric to an exact numeric with less scale (integers have a scale of 0), the extra digits of scale beyond the target scale are dropped without rounding the result.

  • If both source and target data type are character strings, the language of the result string is the same as the source.

  • If the source data type is a character string and the target data type is a numeric, then the source value must only contain a character representation of a number. The result of the conversion is the numeric value that string represented.

    If the source value is not a numeric string, an error occurs.

  • If the target data type is CHAR(n), and the source data type is an exact numeric, the result is a character representation of that exact numeric. If the source value is less than zero, the first character of the result is a minus sign. Otherwise, the first character is a number or a decimal point.

    If the length of the resulted string is less than n, then blanks are added on the right. If the length of the resulted string is greater than n, an error occurs. The same algorithm applies if the target data type is VARCHAR(n), except that there is no need to pad the numeric string if its length is less than n.

  • If the target data type is CHAR(n) and the source data type is an approximate numeric, then the number is converted to a character representation in scientific notation.

    If the length of the resulted string is less than n, then blanks are added on the right. If the length of the resulted string is greater than n, then an error occurs. The same algorithm applies if the target data type is VARCHAR(n), except that there is no need to pad the numeric string if its length is less than n.

  • Conversion between character and binary data types is supported implicity as well as with CAST. The same rules still apply with CAST. If a target is shorter than the source, truncation occurs. If the target is larger than the source, the target is zero-filled in the case of BINARY(n), and blank-filled in the case of CHAR(n).

  • When converting a non-character data type to BINARY(n) or VARBINARY(n), the data is not modified. Only the type changes so that the data is treated as binary data. The size of the source and the target in bytes must be equal in the case of BINARY(n), and the size of the source must be less than or equal to the size of the target in the case of VARBINARY(n). Otherwise, an error occurs.

    For decimal numbers, each digit of precision contributes 4 bits and 4 bits for the sign. The overall size is rounded up to a 4-byte boundary. The storage size for DATE, TIME, DATETIME, and INTERVAL is 16 bytes.

  • When converting from BINARY(n) or VARBINARY(n) into a non-character data type, the data is not modified. Only the type changes so that the data is treated as a number of the target data type. The actual size of the source and the target in bytes must be equal, or an error occurs.

  • Conversion between binary data types and numeric data types is an ALLBASE extension and is not allowed according to the ANSI SQL2 standard.

  • Converting a character string to a DATE, TIME, DATETIME or INTERVAL with CAST is equivalent to using the respective date/time function, TO_DATE, TO_TIME, TO_DATETIME, or TO_INTERVAL. All the same rules apply.

  • Using CAST to convert numeric types directly to date/time types is not allowed. This should be done by nesting the CAST functions so that the numeric value is first converted to a character string, and then converted to the date/time data type.

  • Converting a date/time data type to:

    • A character type with CAST is equivalent to using the TO_CHAR date/time function. All the same rules apply.

    • An INTEGER is equivalent to using the TO_INTEGER date/time function. This function converts date/time column value into an INTEGER value which represents a portion of the date/time column. If the source data type of CAST is date/time data type, and the target data type is INTEGER, all rules for TO_INTEGER to convert date/time into INTEGER will be applied. The FormatSpec must be used to specify a single component of the date/time data type (i.e. HH, MM, SS, DAYS, etc.).

    • Other numeric types are also allowed using CAST. In this case, the date/time data type is first converted to an INTEGER applying all the TO_INTEGER rules, then is converted from INTEGER to the target data type.

Examples

  1. You will see the result has VendorNumber presented as: Vendor9000, Vendor9020,.... 

        CREATE TABLE PurchDB.SupplyPrice 

      ( PartNumber     CHAR(16) NOT CASE SENSITIVE not null unique,

        VendorNumber   INTEGER,

        VendPartNumber CHAR(16) lang=german NOT CASE SENSITIVE,

        UnitPrice      DECIMAL(10,2),

        DeliveryDays   CHAR(2),

        DiscountQty    SMALLINT)



    SELECT PartNumber, 'Vendor' || CAST(VendorNumber AS VARCHAR(4)) 

    FROM PurchDB.SupplyPrice

    WHERE VendorNumber BETWEEN 9000 AND 9020;

  2. You will see the INTERVAL constant shown as: 0 23:00:00:000 

        SELECT PartNumber, CAST(CAST(23,CHAR(2)),INTERVAL,'HH')

    FROM PurchDB.SupplyPrice;

  3. You will see the INTEGER constant shown as: 99 

        SELECT PartNumber, CAST('9999-12-31',INTEGER,'CC')

    FROM PurchDB.SupplyPrice;

  4. SELECT SUM with CAST 

        SELECT SUM(CAST(DeliveryDays, SMALLINT)) 

    FROM PurchDB.SupplyPrice

    WHERE VendorNumber BETWEEN 9000 AND 9020;

  5. EXEC SQL with CAST 

        EXEC SQL begin declare section;

       char hostvar1[16];

       sqlbinary hostvar2[8];

    EXEC SQL end declare section;
    Assume there is only one row qualified for the following query. 
        EXEC SQL select PartNumber, CAST(UnitPrice,BINARY(8))

    INTO :hostvar1, :hostvar2

    FROM PurchDB.SupplyPrice

    WHERE VendorNumber BETWEEN 9000 AND 9020;

  6. You will see the DECIMAL constant shown as: 99.99 

        SELECT PartNumber, CAST(99.99,VARCHAR(10))

    FROM PurchDB.SupplyPrice;



Aggregate Functions
  		 


Constant  
Feedback to webmaster