![]() SELECT BINARY_CHECKSUM(‘ABCDEFG-ABCDEFG’) however if we have 7 or more characters and the same number of characters on each side they are the same these should be different you would imagine add one character to each string that is separated by a ‘-‘ character We’ve found a bit of a potential problem with BINARY_CHECKSUM(), perhaps we are missing something but could you explain if this is intended behavior or a bug? Are you using this feature in your application, if yes, I am interested to know where and when do you use it. You can clearly see when the values are change the value of the BINARY_CHECKSUM is changed as well, however, if the value is changed back to original value the BINARY_CHECKSUM is restored. SELECT BINARY_CHECKSUM (*) AS BCH FROM myTable INSERT INTO myTable VALUES ( 1, 'test' ) IF EXISTS ( SELECT * FROM sys.objects WHERE OBJECT_ID = OBJECT_ID ( N'.' ) AND TYPE IN ( N'U' ))ĬREATE TABLE myTable ( column1 INT, column2 VARCHAR ( 256 )) Let us see quick example of the of same.įollowing example is modified from the original example taken from BOL. However, if the row is changed from A to B and once again changed back to A, the BINARY_CHECKSUM cannot be used to detect the changes. If any row has any value changed, this function can be used to figure out if the values are changed in the rows. This is usually used to detect changes in a row. So, “2Volvo Director 20” and “3Volvo Director 30” will yield the same value, however the CHECKSUM() function evaluates the type as well as compares the two strings and if they are equal, then only the same value is returned.In one of the recent consultancy, I was asked if I can give working example of BINARY_CHECKSUM. BINARY_CHECKSUM() returns the same value if the elements of two expressions have the same type and byte representation. An example of such a difference is the values generated for “DECIPHER” and “decipher” will be different in the case of a BINARY_CHECKSUM but will be the same for the CHECKSUM function (assuming that we have a case insensitive installation of the instance).Īnother difference is in the comparison of expressions. The difference between CHECKSUM and BINARY_CHECKSUM is in the value generated for the string data-types. This also works with the new analytic function’s OVER clause in SQL Server 2005.īINARY_CHECKSUM: As the name states, this returns the binary checksum value computed over a row or a list of expressions. There are three checksum functions available to you:ĬHECKSUM_AGG: This returns the checksum of the values in a group and Null values are ignored in this case. So, if you have to use a datetime data-type column, then make sure that you get the exact date + hour/min. So, explicitly define the column listing.īe careful when you include the datetime data-type columns since the granularity is 1/300th of a second and even a small variation will result into a different checksum value. We would not recommend using checksum(*) since the value that will get generated that way will be based on the column order of the table definition at run time which can easily change over a period of time. You need to make sure that the column(s) or expression order is the same between the two checksums that are being compared else the value would be different and will lead to issues. SQL Server Books Online has a lot of examples on this piece of functionality.Ī couple of things to watch out for when using these functions: ![]() ![]() This mechanism can then be used instead of joining with all the columns that make the record unique to see whether the record has been updated or not. If say you use it to compute and store a column at the table level to denote the checksum over the columns that make a record unique in a table, then this can be helpful in determining whether a row has changed or not. The key intent of the CHECKSUM functions is to build a hash index based on an expression or a column list. Check out the following blog post that highlights the diferences.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |