Add support for expressions

[michael-simons]

From sql2cypher created by lukaseder: neo4j-contrib/sql2cypher#10

I'll implement more of the expressions() method, to support:

Functions

• Arithmetic expressions
• https://neo4j.com/docs/cypher-manual/current/functions/mathematical-numeric/
• https://neo4j.com/docs/cypher-manual/current/functions/mathematical-logarithmic/
• https://neo4j.com/docs/cypher-manual/current/functions/mathematical-trigonometric/
• https://neo4j.com/docs/cypher-manual/current/functions/string/
  • Note, there's still quite a few missing features in Cypher-DSL here
• https://neo4j.com/docs/cypher-manual/current/functions/temporal/
• https://neo4j.com/docs/cypher-manual/current/functions/temporal/duration/
• https://neo4j.com/docs/cypher-manual/current/functions/spatial/ (won't be available with the jOOQ Open Source edition)
  • While the parser and QOM API don't have a representation for these things in the jOOQ Open Source Edition, we can specify Settings.parseUnknownFunctions and try to translate things from there.
• https://neo4j.com/docs/cypher-manual/current/functions/scalar/

Query syntax

• CASE https://neo4j.com/docs/cypher-manual/current/syntax/expressions/#query-syntax-case
  • CASE abbreviations
  • CASE simple
  • CASE searched
• EXISTS (currently not supported in Cypher-DSL, with subqueries?)
• COUNT (doesn't have the exact SQL equivalent)

Not yet possible:

• https://neo4j.com/docs/cypher-manual/current/functions/aggregating/ (still missing jOOQ QOM support, will implement next week)

[michael-simons]

Really great work on the expressions so far and the TCK works really well.