Call now: (800) 766-1884  



 Home


 SQL Server Tips
 SQL Server Training

 SQL Server Consulting
 SQL Server Support
 SQL Server Remote DBA



 Articles
 Services
 SQL Server Scripts
 Scripts Menu



 

 

 

   
  SQL Server Tips by Gama and Naughter

Handling different data types

xp_palindrome, srv_willconvert and srv_convert

This XP takes an input of any data type and returns true if the input is a palindrome. The returned value is stored in an output parameter of data type boolean. The XP works with character, numeric and binary data.

In TSQL all data conversions or castings both implicit and explicit, convert the value of the data from one data type to another based on the data representation and not the underlying raw data. For example an int is stored as four bytes and it can be converted to binary or CHAR:

DECLARE @i int
SET @i=12345
PRINT CAST(@i as varbinary)
PRINT CAST(@i as varchar)

Output:
0x00003039
12345


The variable @i is stored in four bytes and it can be converted to a binary data type with the exact same raw data. In contrast, converting to a varchar changes the length of the data from four to five bytes as well as modifying its contents. Instead of storing the value of @i in a 32-bit binary number, the data will be stored in five bytes, each one with one ASCII character from the value of @i.
Converting from int to real will have no loss of precision due to rounding, in this example. The two data types are stored in four bytes of data but the data is quite different, despite representing the same value:

PRINT CAST(@i as real)
PRINT CAST( CAST(@i as real) as varbinary)

Output:
12345
0x4640E400

Data type conversions by using C++ functions like atoi, atof, MultiByteToWideChar, etc. are possible in an XP but not necessary. ODS comes with several functions for simplifying the process of data type conversions. The two more interesting functions are srv_willconvert and srv_convert.

The srv_willconvert function returns TRUE if a conversion between two data types is legal and FALSE otherwise. For example, binary to real is not accepted. This function is very helpful because it will reject unacceptable conversions. It is almost always used preceding a call to srv_convert.

The srv_convert function will convert from one ODS data type to another. It mirrors the data type conversion functionality, which is available in TSQL.

int srv_convert (SRV_PROC * srvproc, int srctype, void * src, DBINT srclen, int desttype, void * dest, DBINT destlen )


The above book excerpt is from:

Super SQL Server Systems
Turbocharge Database Performance with C++ External Procedures

ISBN: 0-9761573-2-2
Joseph Gama, P. J. Naughter

 http://www.rampant-books.com/book_2005_2_sql_server_external_procedures.htm  

 

Burleson Consulting Remote DB Administration


 

 


 

 

 

 

 
Burleson is the America's Team

Note: The pages on this site were created as a support and training reference for use by our staff of DBA consultants.  If you find it confusing, please exit this page.

Errata?  SQL Server technology is changing and we strive to update our SQL Server support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:and include the URL for the page.
 


Burleson Consulting
SQL Server database support

 

Copyright 1996 -  2013 by Vaaltech Web Services. All rights reserved.

Hit Counter