[GitHub] [incubator-druid] xueyumusic commented on issue #7281: bump calcite version to 1.18.0 in druid-sql

[GitBox <gi...@apache.org>]

xueyumusic commented on issue #7281: bump calcite version to 1.18.0 in druid-sql
URL: https://github.com/apache/incubator-druid/pull/7281#issuecomment-482790886
 
 
   > @xueyumusic, thanks for looking into this. Please check out the comment on the test "testNullStringEquality" - what do you think?
   
   Hi, @gianm , thanks a lot for review. 
   The plan `[CASE(=($0, 'a'), =(null, null), =($0, null))]`'s part `=($0, null)` is simplified as `unknownAs` value which is `false` [at here](https://github.com/apache/calcite/blob/branch-1.18/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L250). Since the UNKNOWN policy of equal is [ANY](https://github.com/apache/calcite/blob/branch-1.18/core/src/main/java/org/apache/calcite/plan/Strong.java#L209) so if at least one of its arguments is null [then expr value is null(unknown)](https://github.com/apache/calcite/blob/branch-1.18/core/src/main/java/org/apache/calcite/plan/Strong.java#L113).
   For `=(null, null)`, `DruidRexExecutor` reduces it as True
   
   One way might be that modify `DruidRexExecutor` to keep the same policy as calcite as following (adding strong.isNull check) 
   ```
           if (sqlTypeName == SqlTypeName.BOOLEAN) {
             if (strong.isNull(constExp) && constExp.getKind() == SqlKind.EQUALS) {
               literal = rexBuilder.makeLiteral(false); //unknownAs is false
             } else {
               literal = rexBuilder.makeLiteral(exprResult.asBoolean(), constExp.getType(), true);
             }
           }
   ```
   But this way will reduce `=(null, null)` and `=(null, '')`(useDefaultValueForNull) as false, so the test `testEmptyStringEquality`'s result will be affected too and `=(null, null)` as false is a little counter-intuitive
   What do you think, thanks!

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