Noticed while studying nearby code
* allow_merge: true if check constraints may be merged with existing ones
* is_local: true if definition is local, false if it's inherited
* is_internal: true if result of some internal process, not a user request
+ * queryString: used during expression transformation of default values and
+ * cooked CHECK constraints
*
* All entries in newColDefaults will be processed. Entries in newConstraints
* will be processed only if they are CONSTR_CHECK type.