Left join

x lj y lj [x;y] x ljf y ljf[x;y]

Where

x is a table
y is
- a keyed table whose key column/s are columns of x, returns x and y joined on the key columns of y
- or the general empty list (), returns x

For each record in x, the result has one record with the columns of y joined to columns of y:

if there is a matching record in y, it is joined to the x record; common columns are replaced from y.
if there is no matching record in y, common columns are left unchanged, and new columns are null