wangzhigang1999 commented on code in PR #7419:
URL: https://github.com/apache/kyuubi/pull/7419#discussion_r3154003255
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externals/kyuubi-jdbc-engine/src/main/scala/org/apache/kyuubi/engine/jdbc/dialect/MySQLDialect.scala:
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@@ -122,6 +150,16 @@ class MySQLDialect extends JdbcDialect {
query.toString()
}
+ override def setSchema(conn: Connection, schema: String): Unit = {
+ // mysql-connector-j makes setCatalog/setSchema mutually exclusive based
on the
+ // `databaseTerm` connection property: with the default CATALOG,
setCatalog issues
+ // COM_INIT_DB and setSchema is a silent no-op; with SCHEMA it is the
inverse.
+ // Calling both means exactly one fires regardless of how the user
configured the
+ // URL. StarRocksDialect / DorisDialect inherit this via MySQLDialect.
+ conn.setCatalog(schema)
+ conn.setSchema(schema)
Review Comment:
Good point to think through. The dual `setCatalog` + `setSchema` is safe
because mysql-connector-j picks one of the two to actually send and silently
swallows the other inside the driver, based on its `databaseTerm` connection
property: with the default `CATALOG`, `setCatalog` sends a "switch database"
command and `setSchema` does nothing; with `SCHEMA` it's the reverse. So no
matter how the user configured the URL, the StarRocks/Doris server only ever
receives one "switch database" command, never two.
Confirmed by reading the driver source — both methods funnel into the same
`setDatabase(...)` call after the `databaseTerm` check, see
[`ConnectionImpl.java#L2145`](https://github.com/mysql/mysql-connector-j/blob/release/9.x/src/main/user-impl/java/com/mysql/cj/jdbc/ConnectionImpl.java#L2145).
`setCatalog` is literally `if (databaseTerm == CATALOG) setDatabase(catalog);`
and `setSchema` is the symmetric `if (databaseTerm == SCHEMA)
setDatabase(schema);` — exactly one branch fires per call site, neither throws
when its branch is skipped.
The server treats that command as "switch the current database" — it does
**not** treat it as "switch catalog" (catalog switching on StarRocks/Doris is a
separate `SET CATALOG` SQL statement, not something the MySQL protocol can do).
The name we pass in comes from `USE_DATABASE`, which the Hive JDBC driver
parses out of the URL path. The Hive URL syntax has no concept of catalog, so
this name is always a database in the current (default) catalog.
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