Now many DBs have support implicit type cast, eg: SqlServer, Oracle, Hive.
Implicit type cast is an useful function for many cases, So we should support this.
I checkout Calcite code and found that:
- Now we use a validator to validate our operands types[ through kinds of namespaces and scopes ]
- Most of the validations will finally goes to
- which will use validation logic defined in corresponding SqlOperandTypeChecker
What i'm confused about is where should i put the implicit type cast logic in? I figured out 2 ways:
- Supply a tool class/rules to add casts into a parsed SqlNode tree which will then go through the validation logic later on.
- Unleash the validation logic in kinds of SqlOperandTypeChecker, then modify the RelNode/RexNodes tree converted from a validated SqlNode tree to add in casts through custom RelOptRules.
So guys, which of the 2 ways should i go, or if there are better way to do this?
I need your help.
Hi guys, i have made a PR in CALCITE-2302
This is design doc: Calcite Implicit Type Cast Design.
This is the type conversion matrix: Type Conversion Matrix.
I really appreciate your suggestions, thx.