spark DerbyDialect 源码

2022-10-20
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spark DerbyDialect 代码

文件路径：/sql/core/src/main/scala/org/apache/spark/sql/jdbc/DerbyDialect.scala

/*
 * 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.jdbc

import java.sql.Types
import java.util.Locale

import org.apache.spark.sql.errors.QueryExecutionErrors
import org.apache.spark.sql.types._


private object DerbyDialect extends JdbcDialect {

  override def canHandle(url: String): Boolean =
    url.toLowerCase(Locale.ROOT).startsWith("jdbc:derby")

  // See https://db.apache.org/derby/docs/10.15/ref/index.html
  private val supportedAggregateFunctions = Set("MAX", "MIN", "SUM", "COUNT", "AVG",
    "VAR_POP", "VAR_SAMP", "STDDEV_POP", "STDDEV_SAMP")
  private val supportedFunctions = supportedAggregateFunctions

  override def isSupportedFunction(funcName: String): Boolean =
    supportedFunctions.contains(funcName)

  override def getCatalystType(
      sqlType: Int, typeName: String, size: Int, md: MetadataBuilder): Option[DataType] = {
    if (sqlType == Types.REAL) Option(FloatType) else None
  }

  override def getJDBCType(dt: DataType): Option[JdbcType] = dt match {
    case StringType => Option(JdbcType("CLOB", java.sql.Types.CLOB))
    case ByteType => Option(JdbcType("SMALLINT", java.sql.Types.SMALLINT))
    case ShortType => Option(JdbcType("SMALLINT", java.sql.Types.SMALLINT))
    case BooleanType => Option(JdbcType("BOOLEAN", java.sql.Types.BOOLEAN))
    // 31 is the maximum precision and 5 is the default scale for a Derby DECIMAL
    case t: DecimalType if t.precision > 31 =>
      Option(JdbcType("DECIMAL(31,5)", java.sql.Types.DECIMAL))
    case _ => None
  }

  override def isCascadingTruncateTable(): Option[Boolean] = Some(false)

  // See https://db.apache.org/derby/docs/10.15/ref/rrefsqljrenametablestatement.html
  override def renameTable(oldTable: String, newTable: String): String = {
    s"RENAME TABLE $oldTable TO $newTable"
  }

  // Derby currently doesn't support comment on table. Here is the ticket to add the support
  // https://issues.apache.org/jira/browse/DERBY-7008
  override def getTableCommentQuery(table: String, comment: String): String = {
    throw QueryExecutionErrors.commentOnTableUnsupportedError()
  }

  override def getLimitClause(limit: Integer): String = {
    ""
  }
}

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