Sometimes it is necessary to make sure that content of two tables are the same or to monitor changes to the table.
For example for MS SQL it is possible to do that with CHECKSUM_AGG function
SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM table
As far as I know there is no similar aggregation function for Sybase ASE, but some close functionality can be achieved with XOR + update trick
create procedure sp__hashcode
@objectname varchar(255)
,@excludelist varchar(16384) = null
,@includelist varchar(16384) = null
,@whereclause varchar(16384) = null
,@hashalgorithm varchar(20) = 'MD5'
,@using varchar(255) = null
,@hash bigint = 0 output
,@debug bit = 1
as
begin declare @objectid int ,@columnlist varchar(16384) ,@rowcount int select @objectid = object_id(@objectname), @hash = isnull(@hash,0) if @objectid is null begin /* 17461, "Object does not exist in this database." */ raiserror 17461 return (1) end /* Create temporary table for column list */ create table #columnlist ( name varchar(255) ) insert into #columnlist select distinct c.name from syscolumns c join systypes t on (c.type = t.type) where c.id = @objectid and t.name not in ('image','text','unitext') -- ignore LOBs and (isnull(c.xstatus,0) & 1) != 1 -- ignore off row /* Delete columns which exists in exclude list */ if @excludelist is not null begin set @excludelist = str_replace(@excludelist, '''', '''''') set @excludelist = '''' + str_replace(@excludelist, ',', ''',''') + '''' if @debug = 1 print 'Exclude list: %1!', @excludelist execute ('delete from #columnlist where name in (' + @excludelist + ')') end /* Delete columns which not exists in include list */ if @includelist is not null begin set @includelist = str_replace(@includelist, '''', '''''') set @includelist = '''' + str_replace(@includelist, ',', ''',''') + '''' if @debug = 1 print 'Include list: %1!', @includelist execute ('delete from #columnlist where name not in (' + @includelist + ')') end /* Put columns into the comma separated list */ update #columnlist set @columnlist = @columnlist + case when @columnlist is null then null else ',' end + name if @debug = 1 print 'Column list: %1!', @columnlist if @columnlist is not null if @using is null execute ( 'update ' + @objectname + ' set @hash=@hash^convert(bigint,hashbytes(''' + @hashalgorithm + ''',' + @columnlist + ')) ' + @whereclause ) else execute ( 'update ' + @objectname + ' set @hash=@hash^convert(bigint,hashbytes(''' + @hashalgorithm + ''',' + @columnlist + ',using ' + @using + ')) ' + @whereclause ) select @rowcount = @@rowcount if @debug = 1 begin print 'Rows processed: %1!', @rowcount print 'Hash: %1!', @hash end return (0)
end
goExample of usage:
sp__hashcode sysobjects, @includelist='name,id,uid,type', @whereclause='where id < 20'
Definitely, there is no one hundred percent guarantee that two different tables will return distinct hashes, at least because hashbytes calculates hash based on the underlying bytes, and in case of different data types with same bytes it returns the same value. This query demonstrates it
select hashbytes ('MD5', cast(49 as tinyint)), hashbytes ('MD5', '1') Also it is quite heavy, and have other limitations (like lengths of column names) but still useful for quick comparation of tables and watching for changes for relevantly small tables.
p.s. criticism is welcome