For comments.

Author: viirya

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRDD.scala

@@ -318,17 +318,21 @@ private[sql] class JDBCRDD(
   /**
    * `filters`, but as a WHERE clause suitable for injection into a SQL query.
    */
-  private val filterWhereClause: Seq[Option[String]] = filters.map(JDBCRDD.compileFilter)
+  private val filterWhereClause: String =
+    filters.map(JDBCRDD.compileFilter).flatten.mkString(" AND ")
 
   /**
    * A WHERE clause representing both `filters`, if any, and the current partition.
    */
   private def getWhereClause(part: JDBCPartition): String = {
-    val w = filterWhereClause.+:(Option(part.whereClause)).flatten.mkString(" AND ")
-    if (!w.isEmpty) {
-      "WHERE " + w
+    if (part.whereClause != null && filterWhereClause.length > 0) {
+      "WHERE " + filterWhereClause + " AND " + part.whereClause
+    } else if (part.whereClause != null) {
+      "WHERE " + part.whereClause
+    } else if (filterWhereClause.length > 0) {
+      "WHERE " + filterWhereClause
     } else {
-      w
+      ""
     }
   }
 

sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala

@@ -190,7 +190,7 @@ class JDBCSuite extends SparkFunSuite
     assert(stripSparkFilter(sql("SELECT * FROM foobar WHERE NAME IN ('mary', 'fred')"))
       .collect().size == 2)
     assert(stripSparkFilter(sql("SELECT * FROM foobar WHERE NAME NOT IN ('fred')"))
-      .collect().size === 2)
+      .collect().size == 2)
     assert(stripSparkFilter(sql("SELECT * FROM foobar WHERE THEID = 1 OR NAME = 'mary'"))
       .collect().size == 2)
     assert(stripSparkFilter(sql("SELECT * FROM foobar WHERE THEID = 1 OR NAME = 'mary' "
@@ -473,6 +473,7 @@ class JDBCSuite extends SparkFunSuite
       === "(NOT (col1 IN ('mno', 'pqr')))")
     assert(doCompileFilter(IsNull("col1")) === "col1 IS NULL")
     assert(doCompileFilter(IsNotNull("col1")) === "col1 IS NOT NULL")
+    assert(doCompileFilter(And(EqualNullSafe("col0", "abc"), EqualTo("col1", "def"))) === "")
   }
 
   test("Dialect unregister") {