Add show variable executor for OpenGauss (#34044)

* Add show variable executor for OpenGauss

* Fix checkstyle

* Fix test error

proxy/backend/type/opengauss/src/main/java/org/apache/shardingsphere/proxy/backend/opengauss/handler/admin/OpenGaussAdminExecutorCreator.java

@@ -26,6 +26,8 @@
 import org.apache.shardingsphere.proxy.backend.postgresql.handler.admin.PostgreSQLAdminExecutorCreator;
 import org.apache.shardingsphere.sql.parser.statement.core.segment.dml.item.ExpressionProjectionSegment;
 import org.apache.shardingsphere.sql.parser.statement.core.segment.dml.item.ProjectionSegment;
+import org.apache.shardingsphere.sql.parser.statement.core.statement.SQLStatement;
+import org.apache.shardingsphere.sql.parser.statement.core.statement.dal.ShowStatement;
 import org.apache.shardingsphere.sql.parser.statement.core.statement.dml.SelectStatement;
 
 import java.util.Collection;
@@ -66,7 +68,11 @@ public final class OpenGaussAdminExecutorCreator implements DatabaseAdminExecuto
 
     @Override
     public Optional<DatabaseAdminExecutor> create(final SQLStatementContext sqlStatementContext) {
-        return delegated.create(sqlStatementContext);
+        SQLStatement sqlStatement = sqlStatementContext.getSqlStatement();
+        if (sqlStatement instanceof ShowStatement) {
+            return Optional.of(new OpenGaussShowVariableExecutor((ShowStatement) sqlStatement));
+        }
+        return Optional.empty();
     }
 
     @Override

proxy/backend/type/opengauss/src/main/java/org/apache/shardingsphere/proxy/backend/opengauss/handler/admin/OpenGaussShowVariableExecutor.java

@@ -0,0 +1,88 @@
+/*
+ * 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.opengauss.handler.admin;
+
+import com.cedarsoftware.util.CaseInsensitiveMap;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import org.apache.shardingsphere.infra.executor.sql.execute.result.query.QueryResultMetaData;
+import org.apache.shardingsphere.infra.executor.sql.execute.result.query.impl.raw.metadata.RawQueryResultColumnMetaData;
+import org.apache.shardingsphere.infra.executor.sql.execute.result.query.impl.raw.metadata.RawQueryResultMetaData;
+import org.apache.shardingsphere.infra.merge.result.MergedResult;
+import org.apache.shardingsphere.infra.merge.result.impl.local.LocalDataMergedResult;
+import org.apache.shardingsphere.infra.merge.result.impl.local.LocalDataQueryResultRow;
+import org.apache.shardingsphere.proxy.backend.handler.admin.executor.DatabaseAdminQueryExecutor;
+import org.apache.shardingsphere.proxy.backend.postgresql.handler.admin.executor.PostgreSQLShowVariableExecutor;
+import org.apache.shardingsphere.proxy.backend.session.ConnectionSession;
+import org.apache.shardingsphere.sql.parser.statement.core.statement.dal.ShowStatement;
+
+import java.sql.Types;
+import java.util.Collections;
+import java.util.Locale;
+import java.util.Map;
+
+/**
+ * OpenGauss show variable executor.
+ */
+@RequiredArgsConstructor
+public final class OpenGaussShowVariableExecutor implements DatabaseAdminQueryExecutor {
+
+    private static final Map<String, OpenGaussShowVariableExecutor.VariableRowDataGenerator> VARIABLE_ROW_DATA_GENERATORS = new CaseInsensitiveMap<>(1, 1F);
+
+    static {
+        VARIABLE_ROW_DATA_GENERATORS.put("sql_compatibility", connectionSession -> new String[]{"sql_compatibility", "PG", "Show sql_compatibility value."});
+    }
+
+    private final ShowStatement showStatement;
+
+    private final PostgreSQLShowVariableExecutor delegated;
+
+    @Getter
+    private QueryResultMetaData queryResultMetaData;
+
+    @Getter
+    private MergedResult mergedResult;
+
+    public OpenGaussShowVariableExecutor(final ShowStatement showStatement) {
+        this.showStatement = showStatement;
+        delegated = new PostgreSQLShowVariableExecutor(showStatement);
+    }
+
+    @Override
+    public void execute(final ConnectionSession connectionSession) {
+        String name = showStatement.getName().orElse("").toLowerCase(Locale.ROOT);
+        if (VARIABLE_ROW_DATA_GENERATORS.containsKey(name)) {
+            queryResultMetaData = new RawQueryResultMetaData(Collections.singletonList(new RawQueryResultColumnMetaData("", "", name, Types.VARCHAR, "VARCHAR", -1, 0)));
+            OpenGaussShowVariableExecutor.VariableRowDataGenerator variableRowDataGenerator = VARIABLE_ROW_DATA_GENERATORS.getOrDefault(name, unused -> new String[]{"", "", ""});
+            mergedResult = new LocalDataMergedResult(Collections.singletonList(new LocalDataQueryResultRow(variableRowDataGenerator.getVariable(connectionSession)[1])));
+        } else {
+            delegated(connectionSession);
+        }
+    }
+
+    private void delegated(final ConnectionSession connectionSession) {
+        delegated.execute(connectionSession);
+        queryResultMetaData = delegated.getQueryResultMetaData();
+        mergedResult = delegated.getMergedResult();
+    }
+
+    private interface VariableRowDataGenerator {
+
+        Object[] getVariable(ConnectionSession connectionSession);
+    }
+}

proxy/backend/type/opengauss/src/test/java/org/apache/shardingsphere/proxy/backend/opengauss/handler/admin/OpenGaussAdminExecutorFactoryTest.java

@@ -22,6 +22,7 @@
 import org.apache.shardingsphere.proxy.backend.handler.admin.executor.DatabaseAdminExecutor;
 import org.apache.shardingsphere.proxy.backend.postgresql.handler.admin.PostgreSQLAdminExecutorCreator;
 import org.apache.shardingsphere.sql.parser.statement.core.statement.dml.SelectStatement;
+import org.apache.shardingsphere.sql.parser.statement.opengauss.dal.OpenGaussShowStatement;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -55,13 +56,11 @@ void setup() throws ReflectiveOperationException {
     }
 
     @Test
-    void assertNewInstanceWithSQLStatementContextOnly() {
+    void assertNewInstanceWithSQLStatementContext() {
         SQLStatementContext sqlStatementContext = mock(SQLStatementContext.class);
-        DatabaseAdminExecutor expected = mock(DatabaseAdminExecutor.class);
-        when(postgresqlAdminExecutorFactory.create(sqlStatementContext)).thenReturn(Optional.of(expected));
+        when(sqlStatementContext.getSqlStatement()).thenReturn(new OpenGaussShowStatement("all"));
         Optional<DatabaseAdminExecutor> actual = openGaussAdminExecutorFactory.create(sqlStatementContext);
         assertTrue(actual.isPresent());
-        assertThat(actual.get(), is(expected));
     }
 
     @Test

proxy/backend/type/opengauss/src/test/java/org/apache/shardingsphere/proxy/backend/opengauss/handler/admin/OpenGaussShowVariableExecutorTest.java

@@ -0,0 +1,80 @@
+/*
+ * 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.opengauss.handler.admin;
+
+import org.apache.shardingsphere.infra.autogen.version.ShardingSphereVersion;
+import org.apache.shardingsphere.infra.executor.sql.execute.result.query.QueryResultMetaData;
+import org.apache.shardingsphere.infra.merge.result.MergedResult;
+import org.apache.shardingsphere.proxy.backend.session.ConnectionSession;
+import org.apache.shardingsphere.sql.parser.statement.opengauss.dal.OpenGaussShowStatement;
+import org.junit.jupiter.api.Test;
+
+import java.sql.SQLException;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.mock;
+
+class OpenGaussShowVariableExecutorTest {
+
+    @Test
+    void assertExecuteShowAll() throws SQLException {
+        ConnectionSession connectionSession = mock(ConnectionSession.class);
+        OpenGaussShowVariableExecutor executor = new OpenGaussShowVariableExecutor(new OpenGaussShowStatement("ALL"));
+        executor.execute(connectionSession);
+        QueryResultMetaData actualMetaData = executor.getQueryResultMetaData();
+        assertThat(actualMetaData.getColumnCount(), is(3));
+        assertThat(actualMetaData.getColumnLabel(1), is("name"));
+        assertThat(actualMetaData.getColumnLabel(2), is("setting"));
+        assertThat(actualMetaData.getColumnLabel(3), is("description"));
+        MergedResult actualResult = executor.getMergedResult();
+        Map<String, String> expected = new LinkedHashMap<>(7, 1F);
+        expected.put("application_name", "PostgreSQL");
+        expected.put("client_encoding", "UTF8");
+        expected.put("integer_datetimes", "on");
+        expected.put("TimeZone", "Etc/UTC");
+        expected.put("transaction_isolation", "read committed");
+        expected.put("transaction_read_only", "off");
+        expected.put("server_version", ShardingSphereVersion.VERSION);
+        for (Entry<String, String> entry : expected.entrySet()) {
+            assertTrue(actualResult.next());
+            assertThat(actualResult.getValue(1, String.class), is(entry.getKey()));
+            assertThat(actualResult.getValue(2, String.class), is(entry.getValue()));
+        }
+        assertFalse(actualResult.next());
+    }
+
+    @Test
+    void assertExecuteShowOne() throws SQLException {
+        ConnectionSession connectionSession = mock(ConnectionSession.class);
+        OpenGaussShowVariableExecutor executor = new OpenGaussShowVariableExecutor(new OpenGaussShowStatement("sql_compatibility"));
+        executor.execute(connectionSession);
+        QueryResultMetaData actualMetaData = executor.getQueryResultMetaData();
+        assertThat(actualMetaData.getColumnCount(), is(1));
+        assertThat(actualMetaData.getColumnLabel(1), is("sql_compatibility"));
+        MergedResult actualResult = executor.getMergedResult();
+        assertTrue(actualResult.next());
+        assertThat(actualResult.getValue(1, String.class), is("PG"));
+        assertFalse(actualResult.next());
+    }
+}