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Scalar Function Calls

  • Článek

Scalar functions return a value for each row. For example, the absolute value scalar function takes a numeric column as an argument and returns the absolute value of each value in the column. The escape sequence for calling a scalar function is

{fn scalar-function }

where scalar-function is one of the functions listed in Appendix E: Scalar Functions. For more information about the scalar function escape sequence, see Scalar Function Escape Sequence in Appendix C: SQL Grammar.

For example, the following SQL statements create the same result set of uppercase customer names. The first statement uses the escape-sequence syntax. The second statement uses the native syntax for Ingres for OS/2 and is not interoperable.

SELECT {fn UCASE(Name)} FROM Customers  
  
SELECT uppercase(Name) FROM Customers

An application can mix calls to scalar functions that use native syntax and calls to scalar functions that use ODBC syntax. For example, assume that names in the Employee table are stored as a last name, a comma, and a first name. The following SQL statement creates a result set of last names of employees in the Employee table. The statement uses the ODBC scalar function SUBSTRING and the SQL Server scalar function CHARINDEX and will execute correctly only on SQL Server.

SELECT {fn SUBSTRING(Name, 1, CHARINDEX(',', Name) - 1)} FROM Customers

For maximum interoperability, applications should use the CONVERT scalar function to make sure that the output of a scalar function is the required type. The CONVERT function converts data from one SQL data type to the specified SQL data type. The syntax of the CONVERT function is

CONVERT( value_exp , data_type)

where value_exp is a column name, the result of another scalar function, or a literal value, and data_type is a keyword that matches the #define name that is used by a SQL data type identifier as defined in Appendix D: Data Types. For example, the following SQL statement uses the CONVERT function to make sure that the output of the CURDATE function is a date, instead of a timestamp or character data:

INSERT INTO Orders (OrderID, CustID, OpenDate, SalesPerson, Status)  
   VALUES (?, ?, {fn CONVERT({fn CURDATE()}, SQL_DATE)}, ?, ?)

To determine which scalar functions are supported by a data source, an application calls SQLGetInfo with the SQL_CONVERT_FUNCTIONS, SQL_NUMERIC_FUNCTIONS, SQL_STRING_FUNCTIONS, SQL_SYSTEM_FUNCTIONS, and SQL_TIMEDATE_FUNCTIONS options. To determine which conversion operations are supported by the CONVERT function, an application calls SQLGetInfo with any of the options that start with SQL_CONVERT.