[SPARK-44262][SQL] Add dropTable and getInsertStatement to JdbcDialect

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

@@ -78,7 +78,8 @@ object JdbcUtils extends Logging with SQLConfHelper {
    * Drops a table from the JDBC database.
    */
   def dropTable(conn: Connection, table: String, options: JDBCOptions): Unit = {
-    executeStatement(conn, options, s"DROP TABLE $table")
+    val dialect = JdbcDialects.get(options.url)
+    executeStatement(conn, options, dialect.dropTable(table))
   }
 
   /**
@@ -114,22 +115,19 @@ object JdbcUtils extends Logging with SQLConfHelper {
       isCaseSensitive: Boolean,
       dialect: JdbcDialect): String = {
     val columns = if (tableSchema.isEmpty) {
-      rddSchema.fields.map(x => dialect.quoteIdentifier(x.name)).mkString(",")
+      rddSchema.fields
     } else {
       // The generated insert statement needs to follow rddSchema's column sequence and
       // tableSchema's column names. When appending data into some case-sensitive DBMSs like
       // PostgreSQL/Oracle, we need to respect the existing case-sensitive column names instead of
       // RDD column names for user convenience.
-      val tableColumnNames = tableSchema.get.fieldNames
       rddSchema.fields.map { col =>
-        val normalizedName = tableColumnNames.find(f => conf.resolver(f, col.name)).getOrElse {
+        tableSchema.get.find(f => conf.resolver(f.name, col.name)).getOrElse {
           throw QueryCompilationErrors.columnNotFoundInSchemaError(col, tableSchema)
         }
-        dialect.quoteIdentifier(normalizedName)
-      }.mkString(",")
+      }
     }
-    val placeholders = rddSchema.fields.map(_ => "?").mkString(",")
-    s"INSERT INTO $table ($columns) VALUES ($placeholders)"
+    dialect.insertIntoTable(table, columns)
   }
 
   /**

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

@@ -193,6 +193,24 @@ abstract class JdbcDialect extends Serializable with Logging {
     statement.executeUpdate(s"CREATE TABLE $tableName ($strSchema) $createTableOptions")
   }
 
+  /**
+   * Returns an Insert SQL statement template for inserting a row into the target table via JDBC
+   * conn. Use "?" as placeholder for each value to be inserted.
+   * E.g. `INSERT INTO t ("name", "age", "gender") VALUES (?, ?, ?)`
+   *
+   * @param table The name of the table.
+   * @param fields The fields of the row that will be inserted.
+   * @return The SQL query to use for insert data into table.
+   */
+  @Since("4.0.0")
+  def insertIntoTable(
+      table: String,
+      fields: Array[StructField]): String = {
+    val placeholders = fields.map(_ => "?").mkString(",")
+    val columns = fields.map(x => quoteIdentifier(x.name)).mkString(",")
+    s"INSERT INTO $table ($columns) VALUES ($placeholders)"
+  }
+
   /**
    * Get the SQL query that should be used to find if the given table exists. Dialects can
    * override this method to return a query that works best in a particular database.
@@ -542,6 +560,17 @@ abstract class JdbcDialect extends Serializable with Logging {
     }
   }
 
+  /**
+   * Build a SQL statement to drop the given table.
+   *
+   * @param table the table name
+   * @return The SQL statement to use for drop the table.
+   */
+  @Since("4.0.0")
+  def dropTable(table: String): String = {
+    s"DROP TABLE $table"
+  }
+
   /**
    * Build a create index SQL statement.
    *