huaxingao commented on a change in pull request #29396:
URL: https://github.com/apache/spark/pull/29396#discussion_r468266069



##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/jdbc/JDBCScanBuilder.scala
##########
@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.spark.sql.execution.datasources.v2.jdbc
+
+import org.apache.spark.sql.SparkSession
+import org.apache.spark.sql.connector.read.{Scan, ScanBuilder, 
SupportsPushDownFilters, SupportsPushDownRequiredColumns}
+import org.apache.spark.sql.execution.datasources.jdbc.{JDBCOptions, JDBCRDD, 
JDBCRelation}
+import org.apache.spark.sql.jdbc.JdbcDialects
+import org.apache.spark.sql.sources.Filter
+import org.apache.spark.sql.types.StructType
+
+case class JDBCScanBuilder(
+    session: SparkSession,
+    schema: StructType,
+    jdbcOptions: JDBCOptions)
+  extends ScanBuilder with SupportsPushDownFilters with 
SupportsPushDownRequiredColumns {
+
+  private var pushedFilter = Array.empty[Filter]
+
+  private var prunedSchema = schema
+
+  override def pushFilters(filters: Array[Filter]): Array[Filter] = {
+    if (jdbcOptions.pushDownPredicate) {
+      val dialect = JdbcDialects.get(jdbcOptions.url)
+      val (pushed, unSupported) = filters.partition(JDBCRDD.compileFilter(_, 
dialect).isDefined)

Review comment:
       Yes, `compilefilter` is called twice. First time is to check if each of 
the filter can be handled by the underlying database to decide whether to push 
it down or not. Second time to turn the filter into a SQL string 
representation. Both V1JDBC and V2 JDBC behave like this. I think we should be 
able to save the SQL string representation in the first call, so no need to 
call it second time. I will try to fix this. 




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