JDBC H2, `CHAR(10)` column read as `Char?` instead of `String?`

[Jolanrensen]

@zaleslaw
From an H2 database, a CHAR(10) column is read as Char? instead of String?

This issue can be reproduced easily by editing the fun `read from huge table`() in h2Test.kt by adding the line:
schema.columns["characterCol"]!!.type shouldBe typeOf<String?>()
The column contains ["ABC", "DEF", "GHI"] so I gotta agree it's not supposed to be a Char.

I discovered it by exploring whether the DataColumnImpl.type actually matches the types found in DataColumnImpl.values, which mismatches in this case. It might be a good check to do for all type conversions :).

[zaleslaw]

@Jolanrensen what kind of dialect is set by default for H2 in your example?

[Jolanrensen]

@zaleslaw not sure, I just ran your read from huge table test in h2Test.kt, so looking at that file, the connection URL is created like this:

dataframe/dataframe-jdbc/src/test/kotlin/org/jetbrains/kotlinx/dataframe/io/h2Test.kt

Line 21 in e781bf7

private const val URL = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1;MODE=MySQL;DATABASE_TO_UPPER=false"