[SPARK-52929][SQL] Support MySQL and SQLServer connector for DSv2 Join pushdown

### What changes were proposed in this pull request?
Similar to #51594, I am enabling the join pushdown for MySQL and SQLServer connectors.

Additionally, I am moving `JoinPushdownAliasGenerator` to `JdbcSQLQueryBuilder` and using it there as well to generate new subquery alias used for full join subquery (previously, subqueries were generated only for left and right side, but now the whole thing needs to be subqueried). This is needed for these 2 dialects. H2, Oracle and Postgres didn't hit this issue, but they also still work with this, so there is no need for specialization.

### Why are the changes needed?
MySQL and SQLServer connectors don't support join pushdown.

### Does this PR introduce _any_ user-facing change?
No, since the flag `spark.sql.optimizer.datasourceV2JoinPushdown` is disabled. If enabled, it will be attempted to push down to join directly to the scan node.

### How was this patch tested?
New tests.

### Was this patch authored or co-authored using generative AI tooling?

Closes #51637 from PetarVasiljevic-DB/support_join_for_mysql.

Authored-by: Petar Vasiljevic <petar.vasiljevic@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: PetarVasiljevic-DB

connector/docker-integration-tests/src/test/scala/org/apache/spark/sql/jdbc/v2/join/MsSqlServerJoinPushdownIntegrationSuite.scala

@@ -0,0 +1,51 @@
+/*
+ * 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.v2.join
+
+import java.sql.Connection
+import java.util.Locale
+
+import org.apache.spark.sql.jdbc.{DockerJDBCIntegrationSuite, JdbcDialect, MsSQLServerDatabaseOnDocker, MsSqlServerDialect}
+import org.apache.spark.sql.jdbc.v2.JDBCV2JoinPushdownIntegrationSuiteBase
+import org.apache.spark.tags.DockerTest
+
+/**
+ * To run this test suite for a specific version (e.g., 2022-CU15-ubuntu-22.04):
+ * {{{
+ *   ENABLE_DOCKER_INTEGRATION_TESTS=1
+ *   MSSQLSERVER_DOCKER_IMAGE_NAME=mcr.microsoft.com/mssql/server:2022-CU15-ubuntu-22.04
+ *     ./build/sbt -Pdocker-integration-tests "testOnly *v2*MsSqlServerIntegrationSuite"
+ * }}}
+ */
+@DockerTest
+class MsSqlServerJoinPushdownIntegrationSuite
+  extends DockerJDBCIntegrationSuite
+    with JDBCV2JoinPushdownIntegrationSuiteBase {
+  override val db = new MsSQLServerDatabaseOnDocker
+
+  override val url = db.getJdbcUrl(dockerIp, externalPort)
+
+  override val jdbcDialect: JdbcDialect = MsSqlServerDialect()
+
+  override def caseConvert(identifier: String): String = identifier.toUpperCase(Locale.ROOT)
+
+  // This method comes from DockerJDBCIntegrationSuite
+  override def dataPreparation(connection: Connection): Unit = {
+    super.dataPreparation()
+  }
+}

connector/docker-integration-tests/src/test/scala/org/apache/spark/sql/jdbc/v2/join/MySQLJoinPushdownIntegrationSuite.scala

@@ -0,0 +1,50 @@
+/*
+ * 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.v2.join
+
+import java.sql.Connection
+import java.util.Locale
+
+import org.apache.spark.sql.jdbc.{DockerJDBCIntegrationSuite, JdbcDialect, MySQLDatabaseOnDocker, MySQLDialect}
+import org.apache.spark.sql.jdbc.v2.JDBCV2JoinPushdownIntegrationSuiteBase
+import org.apache.spark.tags.DockerTest
+
+/**
+ * To run this test suite for a specific version (e.g., mysql:9.2.0):
+ * {{{
+ *   ENABLE_DOCKER_INTEGRATION_TESTS=1 MYSQL_DOCKER_IMAGE_NAME=mysql:9.2.0
+ *     ./build/sbt -Pdocker-integration-tests "testOnly *v2*MySQLIntegrationSuite"
+ * }}}
+ */
+@DockerTest
+class MySQLJoinPushdownIntegrationSuite
+  extends DockerJDBCIntegrationSuite
+    with JDBCV2JoinPushdownIntegrationSuiteBase {
+  override val db = new MySQLDatabaseOnDocker
+
+  override val url = db.getJdbcUrl(dockerIp, externalPort)
+
+  override val jdbcDialect: JdbcDialect = MySQLDialect()
+
+  override def caseConvert(identifier: String): String = identifier.toUpperCase(Locale.ROOT)
+
+  // This method comes from DockerJDBCIntegrationSuite
+  override def dataPreparation(connection: Connection): Unit = {
+    super.dataPreparation()
+  }
+}

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/jdbc/JDBCScanBuilder.scala

@@ -28,7 +28,7 @@ import org.apache.spark.sql.connector.read.{ScanBuilder, SupportsPushDownAggrega
 import org.apache.spark.sql.execution.datasources.PartitioningUtils
 import org.apache.spark.sql.execution.datasources.jdbc.{JDBCOptions, JDBCPartition, JDBCRDD, JDBCRelation}
 import org.apache.spark.sql.execution.datasources.v2.TableSampleInfo
-import org.apache.spark.sql.jdbc.{JdbcDialects, JdbcSQLQueryBuilder}
+import org.apache.spark.sql.jdbc.{JdbcDialects, JdbcSQLQueryBuilder, JoinPushdownAliasGenerator}
 import org.apache.spark.sql.types.StructType
 
 case class JDBCScanBuilder(
@@ -335,11 +335,3 @@ case class JDBCScanBuilder(
   }
 
 }
-
-object JoinPushdownAliasGenerator {
-  private val subQueryId = new java.util.concurrent.atomic.AtomicLong()
-
-  def getSubqueryQualifier: String = {
-    "join_subquery_" + subQueryId.getAndIncrement()
-  }
-}

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

@@ -200,7 +200,7 @@ class JdbcSQLQueryBuilder(dialect: JdbcDialect, options: JDBCOptions) {
        |$joinType
        |(${right.build()}) $rightSideQualifier
        |ON $joinCondition
-       |)""".stripMargin
+       |) ${JoinPushdownAliasGenerator.getSubqueryQualifier}""".stripMargin
     )
 
     this
@@ -224,3 +224,11 @@ class JdbcSQLQueryBuilder(dialect: JdbcDialect, options: JDBCOptions) {
       s" $whereClause $groupByClause $orderByClause $limitClause $offsetClause"
   }
 }
+
+object JoinPushdownAliasGenerator {
+  private val subQueryId = new java.util.concurrent.atomic.AtomicLong()
+
+  def getSubqueryQualifier: String = {
+    "join_subquery_" + subQueryId.getAndIncrement()
+  }
+}

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

@@ -265,7 +265,7 @@ private case class MsSqlServerDialect() extends JdbcDialect with NoLegacyJDBCErr
       val limitClause = dialect.getLimitClause(limit)
 
       options.prepareQuery +
-        s"SELECT $limitClause $columnList FROM ${options.tableOrQuery}" +
+        s"SELECT $limitClause $columnList FROM $tableOrQuery" +
         s" $whereClause $groupByClause $orderByClause"
     }
   }
@@ -286,6 +286,8 @@ private case class MsSqlServerDialect() extends JdbcDialect with NoLegacyJDBCErr
   }
 
   override def supportsLimit: Boolean = true
+
+  override def supportsJoin: Boolean = true
 }
 
 private object MsSqlServerDialect {

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

@@ -430,7 +430,7 @@ private case class MySQLDialect() extends JdbcDialect with SQLConfHelper with No
       }
 
       options.prepareQuery +
-        s"SELECT $hintClause$columnList FROM ${options.tableOrQuery} $tableSampleClause" +
+        s"SELECT $hintClause$columnList FROM $tableOrQuery $tableSampleClause" +
         s" $whereClause $groupByClause $orderByClause $limitOrOffsetStmt"
     }
   }
@@ -443,4 +443,6 @@ private case class MySQLDialect() extends JdbcDialect with SQLConfHelper with No
   override def supportsOffset: Boolean = true
 
   override def supportsHint: Boolean = true
+
+  override def supportsJoin: Boolean = true
 }

sql/core/src/test/scala/org/apache/spark/sql/jdbc/v2/JDBCV2JoinPushdownIntegrationSuiteBase.scala

@@ -109,7 +109,7 @@ trait JDBCV2JoinPushdownIntegrationSuiteBase
   def schemaPreparation(): Unit = {
     withConnection {conn =>
       conn
-        .prepareStatement(s"CREATE SCHEMA IF NOT EXISTS ${quoteSchemaName(namespace)}")
+        .prepareStatement(s"CREATE SCHEMA ${quoteSchemaName(namespace)}")
         .executeUpdate()
     }
   }