Sam Mason <sam@xxxxxxxxxxxxx> writes: > You just want an extra set of brackets; i.e.: > CREATE INDEX token_position_func ON token ((position+1)); > Should do the trick. Not entirely sure why, but it'll probably have > something to do with avoiding ambiguity in the grammar. Right. The problem is the Berkeley-era decision to put index opclasses into the syntax without any keyword or punctuation, viz create index ... on table (column_name [ opclass_name ]); So something like CREATE INDEX token_position_func ON token (a + b); is ambiguous: is the + an infix operator, or is it a postfix operator and the "b" is to be taken as an opclass name? We hacked around that by requiring parens around expressions. For backwards compatibility with other Berkeley-era syntax, there's a special exception that you can omit the parens when the expression is just a function call. regards, tom lane
