ParseOrdering parses a simple opt.Ordering; for example: "+1,-3".

ParseOrderingChoice parses the string representation of an OrderingChoice for testing purposes.

MinRequired are the default physical properties that require nothing and provide nothing.

OrderingChoice defines the set of possible row orderings that are provided or required by an operator.

OrderingColumnChoice specifies the set of columns which can form one of the columns in the sort key, as well as the direction of that column (ascending or descending).

Provided physical properties of an operator.

Required properties are interesting characteristics of an expression that impact its layout, presentation, or location, but not its logical content.

Presentation specifies the naming, membership (including duplicates), and order of result columns that are required of or provided by an operator.