raql

raql is a small relational algebra query language implemented in Clojure. A query is represented as a vector in prefix notation where the first element is an operator followed by its arguments. The language can be compiled to an abstract syntax tree (AST) and analysed or rewritten programmatically.

Expression language

The following operators are available:

• relation – reference a base relation by keyword
• restrict – filter a relation using boolean expressions (=, <>, <, <=, >=, >, and, or, in)
• project – keep the listed attributes
• project-away – remove the listed attributes
• rename – rename attributes using [old new] pairs
• distinct – remove duplicate tuples
• join, full-join, left-join, right-join – relational joins
• union – combine two relations with identical headings
• order-by – order tuples by attributes
• limit – limit the number of tuples, optionally with an offset

A query can be compiled with fooheads.raql.core/compile which returns an AST enriched with heading information. The AST can be transformed back with fooheads.raql.core/decompile.

Example

(raql/compile
  heading-relmap
  inferrers
  '[project
     [restrict
      [join
       [relation :artist]
       [relation :album]
       [= :artist/id :album/artist-id]]
      [= :artist/name "Jimi Hendrix"]]
     [:artist/name]])

Threading syntax

The function fooheads.raql.syntactic-sugar/expand-threads expands -> threading forms to normal prefix expressions. This makes it possible to write queries in a more natural flow.

(sugar/expand-threads
  '[-> [relation :artist]
       [restrict [< :artist/id 1000]]
       [rename {:artist/id :id}]
       [project [:id]]
       [offset 100]
       [limit 10]])
;; => '[limit
;;      [offset
;;       [project
;;        [rename
;;         [restrict [relation :artist] [< :artist/id 1000]]
;;         {:artist/id :id}]
;;        [:id]]
;;       100]
;;      10]

Rewriting with views

fooheads.raql.rewrite/apply-views replaces [relation <name>] expressions with predefined query expressions. This enables view like abstractions when building larger queries.

Development

This project uses Malli for validation and Clojure for implementation. Run the test suite with:

clojure -X:test

License

Distributed under the [Eclipse Public License 2.0](https://www.eclipse.org/ legal/epl-2.0/).