[SOLVED] How can i convert SqlNode expression(not query!) to RelNode?

How can i convert SqlNode expression(not query!) to RelNode?

I recently start learning Calcite(1.8.0) and i have following use case:

i need to transform a list of strings like "SUM(x) / SUM(y) as myRatio", "MAX(z) as maxZ" or "CASE WHEN …” to AggCalls and use it in RelBuilder later.

So seems like i should do following: convert string -> sql node -> rel node. I converted String to SqlNode using SqlParser.parseExpression and tried Planner.rel(sqlNode) to convert SqlNode to RelNode but no luck. Also tried to create SqlToRelConverter myself, but cannot find out how to create validator, catalog reader and cluster from config created with just JdbcSchema.

Solution

It's a bit tricky, because you're dealing with calls to aggregate functions, and these are not ordinary expressions. Note that an AggCall, used by RelBuilder is neither a SqlNode nor a RexNode.

So, the simplest thing is probably to convert your expression string into a valid query string. E.g. "SUM(x) / SUM(y) as myRatio"" becomes "SELECT SUM(x) / SUM(y) as myRatio FROM (VALUES (0, 0)) AS t(x, y)". Then parse this and convert it to RelNode. PlannerTest.testParseAndConvert does exactly this; it uses only a few lines of code, so you could copy-paste from that method.