wangzhigang1999 commented on code in PR #7419:
URL: https://github.com/apache/kyuubi/pull/7419#discussion_r3151638435
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externals/kyuubi-jdbc-engine/src/main/scala/org/apache/kyuubi/engine/jdbc/dialect/JdbcDialect.scala:
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@@ -82,6 +82,20 @@ abstract class JdbcDialect extends SupportServiceLoader with
Logging {
def getSchemaHelper(): SchemaHelper
+ /**
+ * Switch the current database on the backend connection.
+ *
+ * Called during session open when the client specified a database in the
connection URL
+ * (populated by the Hive JDBC driver into `USE_DATABASE`). Dialects that
support an
+ * in-session database context switch (e.g. MySQL's `USE db`) should
override this and
+ * return `true` on success; the default is a no-op that returns `false`,
meaning the
+ * backend has no notion of "current database" that applies to this session.
+ *
+ * The return value is used by `JdbcOperationManager` to decide whether the
requested
+ * database can be treated as the effective schema filter for metadata
operations.
+ */
+ def setCurrentDatabase(connection: Connection, database: String): Boolean =
false
Review Comment:
Good question — looked into this and it's a bit subtle. `setSchema` doesn't
reliably work for the MySQL family in mysql-connector-j's default config: the
[`databaseTerm` connection
property](https://dev.mysql.com/doc/connector-j/en/connector-j-reference-configuration-properties.html)
selects which of `setCatalog` / `setSchema` actually switches the session
database (the other returns without effect for that mode). Verified by
black-box testing — under default config calling `setSchema` alone does not
change the session database, reproducing the original bug. This also affects
`StarRocksDialect` / `DorisDialect` since they share the same driver — the
property is driver-side, not a server feature.
Two options I'm considering, happy to take direction:
**Option A — keep `USE db` as-is** in `MySQLDialect` (current PR). Simple,
always works regardless of driver config, but it's hand-rolled SQL.
**Option B — go through JDBC standard API, MySQL-family only**:
Keep `JdbcDialect.setCurrentDatabase` as the default no-op returning `false`
(PG / Oracle / etc. unchanged from this PR). Only `MySQLDialect` overrides it:
```scala
// MySQLDialect: invoke both — under mysql-connector-j the databaseTerm
// property selects which one actually switches the database, so calling
// both ensures the switch happens regardless of how the user configured
// the URL. Inherited by StarRocksDialect / DorisDialect.
override def setCurrentDatabase(connection: Connection, database: String):
Boolean = {
connection.setCatalog(database)
connection.setSchema(database)
true
}
```
This still avoids the hand-rolled `USE` SQL and goes through the JDBC
standard API, but doesn't touch any non-MySQL dialect's behavior.
WDYT?
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