ifx_checksum is UDR routine declared as:

create dba function informix.ifx_checksum(informix.bigint, informix.integer)
    returns informix.integer
    with (NOT VARIANT, HANDLESNULLS, PARALLELIZABLE)
    external name '(bigint_checksum)'
    language C;

It works on all basic data types although, you may need to cast character types to LVARCHAR.... i.e. colname::LVARCHAR...

• The first parameters is the column od data to checksum.
• The second parameter is so that we could generate a single checksum on multiple columns.

That way the output of one execution of the ifx_checksum() routine could also be the input of the next. Sort of like chaining the columns together. The innermost call to ifx_checksum needs to have some value as the input value for the second parameter, and you should use zero.

You can nest the calls so that you can generate a single CRC/hash value for multiple columns. As an example suppose that you wanted to hash on three columns, col1, col2, and col3. Then you could write:

SELECT ifx_checksum(col1, ifx_checksum(col2, ifx_checksum(col3, 0)))

You need ifx_checksum(col3, 0) as the inner most function. The zero value is just a place holder to start the function.

As an example suppose that you wanted to limit the hash values between 0 and 1000. You can simply do:

select mod(abs(ifx_checksum(colname, 0)),1000) from syscolumns

But what if you need a MD5 or other hash function. You can easily extend database functions by adding a C or Java UDR.