How to md5 all columns regardless of type

Question

I would like to create a sql query (or plpgsql) that will md5() all given rows regardless of type. However, below, if one is null then the hash is null:

UPDATE t         


        

Answer 1

There is much more elegant solution for this.

In Postgres, using table name in SELECT is permitted and it has type ROW. If you cast this to type TEXT, it gives all columns concatenated together in string that is actually JSON.

Having this, you can get md5 of all columns as follows:

SELECT md5(mytable::TEXT)
FROM mytable

If you want to only use some columns, use ROW constructor and cast it to TEXT:

SELECT md5(ROW(col1, col2, col3)::TEXT)
FROM mytable

Another nice property about this solution is that md5 will be different for NULL vs. empty string.

Obligatory SQLFiddle.