# Produce an (i,j,value) table representing the matrix I(m,n)
# which is the identity matrix if m = n
create or replace function I(m,n,zero) as table (
   with recursive cte(i,j,ij,value) as (
     select 1, 1, (null,null), zero
     union all
     select if(j=n, i+1,  i) as i,
            if(j=n, 1,  j+1) as j,
            (i, j) as ij,
            zero + if(i=j, 1, 0) as value
     from cte
     where i <= m
     )
   select ij[1] as i, ij[2] as j, value
   from cte
   offset 1
);

# Generate a 3x3 matrix with DOUBLE(3,2) values:
from I(3, 3, 0.000);