- case() interprets the "THEN" expressions

- case() interprets the "THEN" expressions
as values by default, meaning case([(x==y, "foo")]) will
interpret "foo" as a bound value, not a SQL expression.
use text(expr) for literal SQL expressions in this case.
For the criterion itself, these may be literal strings
only if the "value" keyword is present, otherwise SA
will force explicit usage of either text() or literal().