[SPARK-22729][SQL] Add getTruncateQuery to JdbcDialect

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

@@ -66,9 +66,9 @@ class JdbcRelationProvider extends CreatableRelationProvider
       if (tableExists) {
         mode match {
           case SaveMode.Overwrite =>
-            if (options.isTruncate && isCascadingTruncateTable(options.url) == Some(false)) {
+            if (options.isTruncate) {
               // In this case, we should truncate table and then load.
-              truncateTable(conn, options.table)
+              truncateTable(conn, options)
               val tableSchema = JdbcUtils.getSchemaOption(conn, options)
               saveTable(df, tableSchema, isCaseSensitive, options)
             } else {

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

@@ -96,20 +96,18 @@ object JdbcUtils extends Logging {
   }
 
   /**
-   * Truncates a table from the JDBC database.
+   * Truncates a table from the JDBC database without side effects.
    */
-  def truncateTable(conn: Connection, table: String): Unit = {
+  def truncateTable(conn: Connection, options: JDBCOptions): Unit = {
+    val dialect = JdbcDialects.get(options.url)
     val statement = conn.createStatement
     try {
-      statement.executeUpdate(s"TRUNCATE TABLE $table")
+      statement.executeUpdate(dialect.getTruncateQuery(options.table))
     } finally {
       statement.close()
     }
   }
 
-  def isCascadingTruncateTable(url: String): Option[Boolean] = {
-    JdbcDialects.get(url).isCascadingTruncateTable()
-  }
 
   /**
    * Returns an Insert SQL statement for inserting a row into the target table via JDBC conn.

sql/core/src/main/scala/org/apache/spark/sql/jdbc/AggregatedDialect.scala

@@ -22,7 +22,7 @@ import org.apache.spark.sql.types.{DataType, MetadataBuilder}
 /**
  * AggregatedDialect can unify multiple dialects into one virtual Dialect.
  * Dialects are tried in order, and the first dialect that does not return a
- * neutral element will will.
+ * neutral element will win.
  *
  * @param dialects List of dialects.
  */
@@ -54,13 +54,7 @@ private class AggregatedDialect(dialects: List[JdbcDialect]) extends JdbcDialect
     dialects.head.getSchemaQuery(table)
   }
 
-  override def isCascadingTruncateTable(): Option[Boolean] = {
-    // If any dialect claims cascading truncate, this dialect is also cascading truncate.
-    // Otherwise, if any dialect has unknown cascading truncate, this dialect is also unknown.
-    dialects.flatMap(_.isCascadingTruncateTable()).reduceOption(_ || _) match {
-      case Some(true) => Some(true)
-      case _ if dialects.exists(_.isCascadingTruncateTable().isEmpty) => None
-      case _ => Some(false)
-    }
+  override def getTruncateQuery(table: String): String = {
+    dialects.head.getTruncateQuery(table)
   }
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/DB2Dialect.scala

@@ -48,5 +48,7 @@ private object DB2Dialect extends JdbcDialect {
     case _ => None
   }
 
-  override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE $table"
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/DerbyDialect.scala

@@ -41,4 +41,8 @@ private object DerbyDialect extends JdbcDialect {
       Option(JdbcType("DECIMAL(31,5)", java.sql.Types.DECIMAL))
     case _ => None
   }
+
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE $table"
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala

@@ -116,6 +116,16 @@ abstract class JdbcDialect extends Serializable {
     s"SELECT * FROM $table WHERE 1=0"
   }
 
+  /**
+   * The SQL query that should be used to truncate a table. Dialects can override this method to
+   * return a query that is suitable for a particular database. For PostgreSQL, for instance,
+   * a different query is used to prevent "TRUNCATE" affecting other tables.
+   * @param table The name of the table.
+   * @return The SQL query to use for truncating a table
+   */
+  @Since("2.3.0")
+  def getTruncateQuery(table: String): String
+
   /**
    * Override connection specific properties to run before a select is made.  This is in place to
    * allow dialects that need special treatment to optimize behavior.
@@ -147,14 +157,6 @@ abstract class JdbcDialect extends Serializable {
     case arrayValue: Array[Any] => arrayValue.map(compileValue).mkString(", ")
     case _ => value
   }
-
-  /**
-   * Return Some[true] iff `TRUNCATE TABLE` causes cascading default.
-   * Some[true] : TRUNCATE TABLE causes cascading.
-   * Some[false] : TRUNCATE TABLE does not cause cascading.
-   * None: The behavior of TRUNCATE TABLE is unknown (default).
-   */
-  def isCascadingTruncateTable(): Option[Boolean] = None
 }
 
 /**

sql/core/src/main/scala/org/apache/spark/sql/jdbc/MsSqlServerDialect.scala

@@ -41,5 +41,7 @@ private object MsSqlServerDialect extends JdbcDialect {
     case _ => None
   }
 
-  override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE $table"
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala

@@ -45,5 +45,7 @@ private case object MySQLDialect extends JdbcDialect {
     s"SELECT 1 FROM $table LIMIT 1"
   }
 
-  override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE $table"
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/OracleDialect.scala

@@ -83,5 +83,7 @@ private case object OracleDialect extends JdbcDialect {
     case _ => value
   }
 
-  override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE $table"
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala

@@ -85,6 +85,17 @@ private object PostgresDialect extends JdbcDialect {
     s"SELECT 1 FROM $table LIMIT 1"
   }
 
+  /**
+  * The SQL query used to truncate a table. For Postgres, the default behaviour is to
+  * also truncate any descendant tables. As this is a (possibly unwanted) side-effect,
+  * the Postgres dialect adds 'ONLY' to truncate only the table in question
+  * @param table The name of the table.
+  * @return The SQL query to use for truncating a table
+  */
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE ONLY $table"
+  }
+
   override def beforeFetch(connection: Connection, properties: Map[String, String]): Unit = {
     super.beforeFetch(connection, properties)
 
@@ -97,8 +108,5 @@ private object PostgresDialect extends JdbcDialect {
     if (properties.getOrElse(JDBCOptions.JDBC_BATCH_FETCH_SIZE, "0").toInt > 0) {
       connection.setAutoCommit(false)
     }
-
   }
-
-  override def isCascadingTruncateTable(): Option[Boolean] = Some(true)
 }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/TeradataDialect.scala

@@ -31,4 +31,8 @@ private case object TeradataDialect extends JdbcDialect {
     case BooleanType => Option(JdbcType("CHAR(1)", java.sql.Types.CHAR))
     case _ => None
   }
+
+  override def getTruncateQuery(table: String): String = {
+    s"TRUNCATE $table"
+  }
 }

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

@@ -752,43 +752,19 @@ class JDBCSuite extends SparkFunSuite
       override def getSchemaQuery(table: String): String = {
         s"My $table Schema"
       }
-      override def isCascadingTruncateTable(): Option[Boolean] = Some(true)
+      override def getTruncateQuery(table: String): String = {
+        s"TRUNCATE $table"
+      }
     }, testH2Dialect))
     assert(agg.canHandle("jdbc:h2:xxx"))
     assert(!agg.canHandle("jdbc:h2"))
     assert(agg.getCatalystType(0, "", 1, null) === Some(LongType))
     assert(agg.getCatalystType(1, "", 1, null) === Some(StringType))
-    assert(agg.isCascadingTruncateTable() === Some(true))
     assert(agg.quoteIdentifier ("Dummy") === "My Dummy quoteIdentifier")
     assert(agg.getTableExistsQuery ("Dummy") === "My Dummy Table")
     assert(agg.getSchemaQuery ("Dummy") === "My Dummy Schema")
   }
 
-  test("Aggregated dialects: isCascadingTruncateTable") {
-    def genDialect(cascadingTruncateTable: Option[Boolean]): JdbcDialect = new JdbcDialect {
-      override def canHandle(url: String): Boolean = true
-      override def getCatalystType(
-        sqlType: Int,
-        typeName: String,
-        size: Int,
-        md: MetadataBuilder): Option[DataType] = None
-      override def isCascadingTruncateTable(): Option[Boolean] = cascadingTruncateTable
-    }
-
-    def testDialects(cascadings: List[Option[Boolean]], expected: Option[Boolean]): Unit = {
-      val dialects = cascadings.map(genDialect(_))
-      val agg = new AggregatedDialect(dialects)
-      assert(agg.isCascadingTruncateTable() === expected)
-    }
-
-    testDialects(List(Some(true), Some(false), None), Some(true))
-    testDialects(List(Some(true), Some(true), None), Some(true))
-    testDialects(List(Some(false), Some(false), None), None)
-    testDialects(List(Some(true), Some(true)), Some(true))
-    testDialects(List(Some(false), Some(false)), Some(false))
-    testDialects(List(None, None), None)
-  }
-
   test("DB2Dialect type mapping") {
     val db2Dialect = JdbcDialects.get("jdbc:db2://127.0.0.1/db")
     assert(db2Dialect.getJDBCType(StringType).map(_.databaseTypeDefinition).get == "CLOB")
@@ -854,6 +830,22 @@ class JDBCSuite extends SparkFunSuite
     assert(derby.getTableExistsQuery(table) == defaultQuery)
   }
 
+  test("truncate table query by jdbc dialect") {
+    val MySQL = JdbcDialects.get("jdbc:mysql://127.0.0.1/db")
+    val Postgres = JdbcDialects.get("jdbc:postgresql://127.0.0.1/db")
+    val db2 = JdbcDialects.get("jdbc:db2://127.0.0.1/db")
+    val h2 = JdbcDialects.get(url)
+    val derby = JdbcDialects.get("jdbc:derby:db")
+    val table = "weblogs"
+    val defaultQuery = s"TRUNCATE $table"
+    val postgresQuery = s"TRUNCATE ONLY $table"
+    assert(MySQL.getTableExistsQuery(table) == defaultQuery)
+    assert(Postgres.getTableExistsQuery(table) == postgresQuery)
+    assert(db2.getTableExistsQuery(table) == defaultQuery)
+    assert(h2.getTableExistsQuery(table) == defaultQuery)
+    assert(derby.getTableExistsQuery(table) == defaultQuery)
+  }
+
   test("Test DataFrame.where for Date and Timestamp") {
     // Regression test for bug SPARK-11788
     val timestamp = java.sql.Timestamp.valueOf("2001-02-20 11:22:33.543543");

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

@@ -46,7 +46,6 @@ class JDBCWriteSuite extends SharedSQLContext with BeforeAndAfter {
 
   val testH2Dialect = new JdbcDialect {
     override def canHandle(url: String) : Boolean = url.startsWith("jdbc:h2")
-    override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
   }
 
   before {