I have a hstore column that has “foo”=>”bar”. I want to add a second key, foo2, with the same value as foo.

Here’s what I’ve tried:

UPDATE mytable
SET mycol = mycol || concat('"foo2"=>"', mycol->'foo', '"')::hstore
WHERE mycol->'foo' IS NOT null

This works for some rows but on others I get the strange error

ERROR: Syntax error near “?” at position 139

What’s the best way to do this?