fix(jdbc): qualify TDengine table preview queries

Closes #6509

crates/dbx-core/src/sql_dialect/table_select.rs

@@ -191,8 +191,16 @@ pub fn build_table_data_select_sql(options: TableDataSelectSqlOptions) -> String
         return format!("{}[1h]", victoriametrics_metric_selector(&options.table_name));
     }
 
+    // TDengine's JDBC connection context setters do not affect WebSocket statements,
+    // so table reads must carry the selected database in the SQL itself.
+    let jdbc_tdengine_database = (database_type == Some(DatabaseType::Jdbc)
+        && options.driver_profile.as_deref().is_some_and(|profile| profile.trim().eq_ignore_ascii_case("tdengine")))
+    .then(|| options.database.as_deref().map(str::trim).filter(|database| !database.is_empty()).or(schema))
+    .flatten();
+    let table = if let Some(database) = jdbc_tdengine_database {
+        qualified_table_name(Some(DatabaseType::Tdengine), Some(database), &options.table_name)
     // Doris / StarRocks multi-catalog: prefix the catalog for external-catalog tables.
-    let table = if uses_connection_identifier_quote(database_type, options.identifier_quote.as_deref()) {
+    } else if uses_connection_identifier_quote(database_type, options.identifier_quote.as_deref()) {
         table_data_qualified_table_name(database_type, schema, &options.table_name, options.identifier_quote.as_deref())
     } else {
         qualified_table_name_with_catalog(

crates/dbx-core/src/sql_dialect/tests.rs

@@ -293,6 +293,53 @@ fn builds_select_sql_with_limit_syntax_for_database_type() {
     );
 }
 
+#[test]
+fn jdbc_tdengine_table_preview_qualifies_selected_database() {
+    assert_eq!(
+        build_table_data_select_sql(TableDataSelectSqlOptions {
+            database_type: Some(DatabaseType::Jdbc),
+            driver_profile: Some(" TDENGINE ".to_string()),
+            schema: None,
+            database: Some("bopu_light".to_string()),
+            table_name: "mppd_pwr_862288087612675".to_string(),
+            limit: Some(100),
+            ..Default::default()
+        }),
+        "SELECT * FROM `bopu_light`.`mppd_pwr_862288087612675`;"
+    );
+
+    assert_eq!(
+        build_table_data_select_sql(TableDataSelectSqlOptions {
+            database_type: Some(DatabaseType::Jdbc),
+            driver_profile: Some("tdengine".to_string()),
+            schema: Some("fallback_db".to_string()),
+            database: Some("   ".to_string()),
+            table_name: "meter`readings".to_string(),
+            limit: Some(100),
+            ..Default::default()
+        }),
+        "SELECT * FROM `fallback_db`.`meter``readings`;"
+    );
+}
+
+#[test]
+fn jdbc_non_tdengine_and_unscoped_tdengine_previews_remain_unqualified() {
+    for (driver_profile, database) in [(Some("postgres"), Some("analytics")), (Some("tdengine"), None)] {
+        assert_eq!(
+            build_table_data_select_sql(TableDataSelectSqlOptions {
+                database_type: Some(DatabaseType::Jdbc),
+                driver_profile: driver_profile.map(str::to_string),
+                schema: None,
+                database: database.map(str::to_string),
+                table_name: "readings".to_string(),
+                limit: Some(100),
+                ..Default::default()
+            }),
+            "SELECT * FROM readings;"
+        );
+    }
+}
+
 #[test]
 fn builds_table_data_where_and_schema_queries() {
     assert_eq!(