table images : { Id : int, Content : blob } table tags : { Id : int, Tag : string } datatype mode = Present | Absent type condition = { Tag : string, Mode : mode } type tag_query = sql_query [] [] [] [Id = int] fun addCondition (c : condition) (q : tag_query) : tag_query = case c.Mode of Present => (SELECT I.Id AS Id FROM ({{q}}) AS I JOIN tags ON tags.Id = I.Id AND tags.Tag = {[c.Tag]}) | Absent => (SELECT I.Id AS Id FROM ({{q}}) AS I LEFT JOIN tags ON tags.Id = I.Id AND tags.Tag = {[c.Tag]} WHERE tags.Tag IS NULL) fun withConditions (cs : list condition) : tag_query = List.foldl addCondition (SELECT images.Id AS Id FROM images) cs fun main (cs : list condition) : transaction page = x <- queryX (withConditions cs) (fn r =>
  • {[r.Id]}
  • ); return {x}