Support information_schema.schemata query

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/TextProtocolBackendHandlerFactory.java

@@ -82,6 +82,10 @@ public static TextProtocolBackendHandler newInstance(final DatabaseType database
         if (sqlStatement instanceof DistSQLStatement) {
             return DistSQLBackendHandlerFactory.newInstance(databaseType, (DistSQLStatement) sqlStatement, backendConnection);
         }
+        Optional<TextProtocolBackendHandler> databaseAdminBackendHandler = DatabaseAdminBackendHandlerFactory.newInstance(databaseType, sqlStatement, backendConnection, sql);
+        if (databaseAdminBackendHandler.isPresent()) {
+            return databaseAdminBackendHandler.get();
+        }
         SQLStatementContext<?> sqlStatementContext = SQLStatementContextFactory.newInstance(
                 ProxyContext.getInstance().getContextManager().getMetaDataContexts().getMetaDataMap(), Collections.emptyList(), sqlStatement, backendConnection.getDefaultSchemaName());
         // TODO optimize SQLStatementSchemaHolder
@@ -101,7 +105,7 @@ public static TextProtocolBackendHandler newInstance(final DatabaseType database
         if (sqlStatement instanceof CreateDatabaseStatement || sqlStatement instanceof DropDatabaseStatement) {
             return DatabaseOperateBackendHandlerFactory.newInstance(sqlStatement, backendConnection);
         }
-        Optional<TextProtocolBackendHandler> databaseAdminBackendHandler = DatabaseAdminBackendHandlerFactory.newInstance(databaseType, sqlStatement, backendConnection);
+        databaseAdminBackendHandler = DatabaseAdminBackendHandlerFactory.newInstance(databaseType, sqlStatement, backendConnection);
         return databaseAdminBackendHandler.orElseGet(() -> DatabaseBackendHandlerFactory.newInstance(sqlStatementContext, sql, backendConnection));
     }
 

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/DatabaseAdminBackendHandlerFactory.java

@@ -43,8 +43,9 @@ public final class DatabaseAdminBackendHandlerFactory {
     }
 
     /**
-     * Create new instance of database admin backend handler. 
-     * 
+     * Create new instance of database admin backend handler,
+     * and this handler requires a connection containing a schema to be used.
+     *
      * @param databaseType database type
      * @param sqlStatement SQL statement
      * @param backendConnection backend connection
@@ -55,7 +56,26 @@ public static Optional<TextProtocolBackendHandler> newInstance(final DatabaseTyp
         if (!executorFactory.isPresent()) {
             return Optional.empty();
         }
-        Optional<DatabaseAdminExecutor> executor = executorFactory.get().newInstance(backendConnection.getSchemaName(), sqlStatement);
+        Optional<DatabaseAdminExecutor> executor = executorFactory.get().newInstance(sqlStatement);
+        return executor.map(optional -> createTextProtocolBackendHandler(sqlStatement, backendConnection, optional));
+    }
+
+    /**
+     * Create new instance of database admin backend handler.
+     *
+     * @param databaseType database type
+     * @param sqlStatement SQL statement
+     * @param backendConnection backend connection
+     * @param sql SQL being executed
+     * @return new instance of database admin backend handler
+     */
+    public static Optional<TextProtocolBackendHandler> newInstance(final DatabaseType databaseType, final SQLStatement sqlStatement,
+                                                                   final BackendConnection backendConnection, final String sql) {
+        Optional<DatabaseAdminExecutorFactory> executorFactory = TypedSPIRegistry.findRegisteredService(DatabaseAdminExecutorFactory.class, databaseType.getName(), new Properties());
+        if (!executorFactory.isPresent()) {
+            return Optional.empty();
+        }
+        Optional<DatabaseAdminExecutor> executor = executorFactory.get().newInstance(sqlStatement, sql);
         return executor.map(optional -> createTextProtocolBackendHandler(sqlStatement, backendConnection, optional));
     }
 

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/DatabaseAdminUpdateBackendHandler.java

@@ -25,6 +25,8 @@
 import org.apache.shardingsphere.proxy.backend.text.admin.executor.DatabaseAdminExecutor;
 import org.apache.shardingsphere.sql.parser.sql.common.statement.SQLStatement;
 
+import java.sql.SQLException;
+
 /**
  * Database admin update backend handler.
  */
@@ -38,7 +40,7 @@ public final class DatabaseAdminUpdateBackendHandler implements TextProtocolBack
     private final DatabaseAdminExecutor executor;
 
     @Override
-    public ResponseHeader execute() {
+    public ResponseHeader execute() throws SQLException {
         executor.execute(backendConnection);
         return new UpdateResponseHeader(sqlStatement);
     }

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/executor/DatabaseAdminExecutor.java

@@ -19,6 +19,8 @@
 
 import org.apache.shardingsphere.proxy.backend.communication.jdbc.connection.BackendConnection;
 
+import java.sql.SQLException;
+
 /**
  * Database admin executor.
  */
@@ -28,6 +30,7 @@ public interface DatabaseAdminExecutor {
      * Execute.
      * 
      * @param backendConnection backend connection
+     * @throws SQLException SQLException
      */
-    void execute(BackendConnection backendConnection);
+    void execute(BackendConnection backendConnection) throws SQLException;
 }

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/executor/DatabaseAdminExecutorFactory.java

@@ -28,11 +28,20 @@
 public interface DatabaseAdminExecutorFactory extends TypedSPI {
 
     /**
-     * New instance of database admin executor.
-     * 
-     * @param currentSchema current schema
+     * Create an instance of database admin executor,
+     * and this executor requires a connection containing a schema to be used.
+     *
      * @param sqlStatement SQL statement
      * @return instance of database admin executor
      */
-    Optional<DatabaseAdminExecutor> newInstance(String currentSchema, SQLStatement sqlStatement);
+    Optional<DatabaseAdminExecutor> newInstance(SQLStatement sqlStatement);
+
+    /**
+     * Create an executor of database admin executor.
+     *
+     * @param sqlStatement SQL statement
+     * @param sql SQL
+     * @return instance of database admin executor
+     */
+    Optional<DatabaseAdminExecutor> newInstance(SQLStatement sqlStatement, String sql);
 }

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/mysql/MySQLAdminExecutorFactory.java

@@ -47,28 +47,32 @@ public final class MySQLAdminExecutorFactory implements DatabaseAdminExecutorFac
     private static final String PERFORMANCE_SCHEMA = "performance_schema";
 
     @Override
-    public Optional<DatabaseAdminExecutor> newInstance(final String currentSchema, final SQLStatement sqlStatement) {
+    public Optional<DatabaseAdminExecutor> newInstance(final SQLStatement sqlStatement) {
+        if (sqlStatement instanceof MySQLShowTablesStatement) {
+            return Optional.of(new ShowTablesExecutor((MySQLShowTablesStatement) sqlStatement));
+        }
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<DatabaseAdminExecutor> newInstance(final SQLStatement sqlStatement, final String sql) {
         if (sqlStatement instanceof UseStatement) {
             return Optional.of(new UseDatabaseExecutor((UseStatement) sqlStatement));
         }
         if (sqlStatement instanceof MySQLShowDatabasesStatement) {
             return Optional.of(new ShowDatabasesExecutor());
         }
-        if (sqlStatement instanceof MySQLShowTablesStatement) {
-            return Optional.of(new ShowTablesExecutor((MySQLShowTablesStatement) sqlStatement));
-        }
         if (sqlStatement instanceof MySQLShowProcessListStatement) {
             return Optional.of(new ShowProcessListExecutor());
         }
         if (sqlStatement instanceof SelectStatement) {
             if (isShowCurrentDatabaseStatement((SelectStatement) sqlStatement)) {
                 return Optional.of(new ShowCurrentDatabaseExecutor());
-            } 
-            if (isQueryInformationSchema(currentSchema, (SelectStatement) sqlStatement)) {
-                // TODO
-                return Optional.empty();
             }
-            if (isQueryPerformanceSchema(currentSchema, (SelectStatement) sqlStatement)) {
+            if (isQueryInformationSchema((SelectStatement) sqlStatement)) {
+                return Optional.of(MySQLInformationSchemaExecutorFactory.newInstance((SelectStatement) sqlStatement, sql));
+            }
+            if (isQueryPerformanceSchema((SelectStatement) sqlStatement)) {
                 // TODO
                 return Optional.empty();
             }
@@ -81,22 +85,19 @@ private boolean isShowCurrentDatabaseStatement(final SelectStatement sqlStatemen
         return firstProjection instanceof ExpressionProjectionSegment && ShowCurrentDatabaseExecutor.FUNCTION_NAME.equalsIgnoreCase(((ExpressionProjectionSegment) firstProjection).getText());
     }
 
-    private boolean isQueryInformationSchema(final String currentSchema, final SelectStatement sqlStatement) {
-        return isQuerySpecialSchema(currentSchema, sqlStatement, INFORMATION_SCHEMA);
+    private boolean isQueryInformationSchema(final SelectStatement sqlStatement) {
+        return isQuerySpecialSchema(sqlStatement, INFORMATION_SCHEMA);
     }
 
-    private boolean isQueryPerformanceSchema(final String currentSchema, final SelectStatement sqlStatement) {
-        return isQuerySpecialSchema(currentSchema, sqlStatement, PERFORMANCE_SCHEMA);
+    private boolean isQueryPerformanceSchema(final SelectStatement sqlStatement) {
+        return isQuerySpecialSchema(sqlStatement, PERFORMANCE_SCHEMA);
     }
 
-    private boolean isQuerySpecialSchema(final String currentSchema, final SelectStatement sqlStatement, final String specialSchemaName) {
+    private boolean isQuerySpecialSchema(final SelectStatement sqlStatement, final String specialSchemaName) {
         TableSegment tableSegment = sqlStatement.getFrom();
         if (!(tableSegment instanceof SimpleTableSegment)) {
             return false;
         }
-        if (specialSchemaName.equalsIgnoreCase(currentSchema) && !((SimpleTableSegment) tableSegment).getOwner().isPresent()) {
-            return true;
-        }
         return ((SimpleTableSegment) tableSegment).getOwner().isPresent() && specialSchemaName.equalsIgnoreCase(((SimpleTableSegment) tableSegment).getOwner().get().getIdentifier().getValue());
     }
 

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/mysql/MySQLInformationSchemaExecutorFactory.java

@@ -0,0 +1,47 @@
+/*
+ * 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.shardingsphere.proxy.backend.text.admin.mysql;
+
+import org.apache.shardingsphere.proxy.backend.text.admin.executor.DatabaseAdminQueryExecutor;
+import org.apache.shardingsphere.proxy.backend.text.admin.mysql.executor.information.SelectSchemataExecutor;
+import org.apache.shardingsphere.sql.parser.sql.common.segment.generic.table.SimpleTableSegment;
+import org.apache.shardingsphere.sql.parser.sql.common.statement.dml.SelectStatement;
+
+/**
+ * Construct the information schema executor's factory.
+ */
+public final class MySQLInformationSchemaExecutorFactory {
+
+    public static final String SCHEMATA = "schemata";
+
+    /**
+     * Create executor.
+     *
+     * @param sqlStatement SQL statement
+     * @param sql SQL being executed
+     * @return executor
+     */
+    public static DatabaseAdminQueryExecutor newInstance(final SelectStatement sqlStatement, final String sql) {
+        String tableName = ((SimpleTableSegment) sqlStatement.getFrom()).getTableName().getIdentifier().getValue();
+        if (SCHEMATA.equalsIgnoreCase(tableName)) {
+            return new SelectSchemataExecutor(sqlStatement, sql);
+        }
+        throw new UnsupportedOperationException(String.format("unsupported table : `%s`", tableName));
+    }
+
+}

shardingsphere-proxy/shardingsphere-proxy-backend/src/main/java/org/apache/shardingsphere/proxy/backend/text/admin/mysql/enums/InformationSchemataEnum.java

@@ -0,0 +1,31 @@
+/*
+ * 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.shardingsphere.proxy.backend.text.admin.mysql.enums;
+
+/**
+ * Enumeration of the fields in the schemata table of the information schema.
+ */
+public enum InformationSchemataEnum {
+
+    CATALOG_NAME,
+    SCHEMA_NAME,
+    DEFAULT_CHARACTER_SET_NAME,
+    DEFAULT_COLLATION_NAME,
+    SQL_PATH,
+    DEFAULT_ENCRYPTION;
+}