[Feat](Nereids) support show variables and show view command

fe/fe-core/src/main/antlr4/org/apache/doris/nereids/DorisParser.g4

@@ -50,11 +50,12 @@ statementBase
     | supportedCreateStatement          #supportedCreateStatementAlias
     | supportedAlterStatement           #supportedAlterStatementAlias
     | materializedViewStatement         #materializedViewStatementAlias
-    | supportedJobStatement              #supportedJobStatementAlias
+    | supportedJobStatement             #supportedJobStatementAlias
     | constraintStatement               #constraintStatementAlias
     | supportedDropStatement            #supportedDropStatementAlias
     | supportedSetStatement             #supportedSetStatementAlias
     | supportedUnsetStatement           #supportedUnsetStatementAlias
+    | supportedShowStatement            #supportedShowStatementAlias
     | unsupportedStatement              #unsupported
     ;
 
@@ -189,6 +190,13 @@ supportedDropStatement
     : DROP CATALOG RECYCLE BIN WHERE idType=STRING_LITERAL EQ id=INTEGER_VALUE #dropCatalogRecycleBin
     ;
 
+supportedShowStatement
+    : SHOW (GLOBAL | SESSION | LOCAL)? VARIABLES wildWhere?                         #showVariables
+    | SHOW VIEW
+        (FROM |IN) tableName=multipartIdentifier
+        ((FROM | IN) database=identifier)?                                          #showView
+    ;
+
 unsupportedOtherStatement
     : HELP mark=identifierOrText                                                    #help
     | INSTALL PLUGIN FROM source=identifierOrText properties=propertyClause?        #installPlugin
@@ -224,7 +232,6 @@ unsupportedShowStatement
     | SHOW STORAGE (VAULT | VAULTS)                                                 #showStorageVault
     | SHOW CREATE REPOSITORY FOR identifier                                         #showCreateRepository
     | SHOW WHITELIST                                                                #showWhitelist
-    | SHOW (GLOBAL | SESSION | LOCAL)? VARIABLES wildWhere?                         #showVariables
     | SHOW OPEN TABLES ((FROM | IN) database=multipartIdentifier)? wildWhere?       #showOpenTables
     | SHOW TABLE STATUS ((FROM | IN) database=multipartIdentifier)? wildWhere?      #showTableStatus
     | SHOW FULL? TABLES ((FROM | IN) database=multipartIdentifier)? wildWhere?      #showTables
@@ -302,9 +309,6 @@ unsupportedShowStatement
     | SHOW (KEY | KEYS | INDEX | INDEXES)
         (FROM |IN) tableName=multipartIdentifier
         ((FROM | IN) database=multipartIdentifier)?                                 #showIndex
-    | SHOW VIEW
-        (FROM |IN) tableName=multipartIdentifier
-        ((FROM | IN) database=multipartIdentifier)?                                 #showView
     | SHOW TRANSACTION ((FROM | IN) database=multipartIdentifier)? wildWhere?       #showTransaction
     | SHOW QUERY PROFILE queryIdPath=STRING_LITERAL                                 #showQueryProfile
     | SHOW LOAD PROFILE loadIdPath=STRING_LITERAL                                   #showLoadProfile

fe/fe-core/src/main/java/org/apache/doris/catalog/Database.java

@@ -497,6 +497,19 @@ public List<Table> getViews() {
         return views;
     }
 
+    public List<Table> getViewsOnIdOrder() {
+        List<Table> tables = idToTable.values().stream()
+                .sorted(Comparator.comparing(Table::getId))
+                .collect(Collectors.toList());
+        List<Table> views = new ArrayList<>();
+        for (Table table : tables) {
+            if (table.getType() == TableType.VIEW) {
+                views.add(table);
+            }
+        }
+        return views;
+    }
+
     /**
      * this method is used for get existed table list by table id list, if table not exist, just ignore it.
      */

fe/fe-core/src/main/java/org/apache/doris/nereids/parser/LogicalPlanBuilder.java

@@ -30,11 +30,13 @@
 import org.apache.doris.catalog.AggregateType;
 import org.apache.doris.catalog.BuiltinAggregateFunctions;
 import org.apache.doris.catalog.Env;
+import org.apache.doris.catalog.InfoSchemaDb;
 import org.apache.doris.catalog.KeysType;
 import org.apache.doris.catalog.ScalarType;
 import org.apache.doris.common.Config;
 import org.apache.doris.common.FeConstants;
 import org.apache.doris.common.Pair;
+import org.apache.doris.datasource.InternalCatalog;
 import org.apache.doris.job.common.IntervalUnit;
 import org.apache.doris.load.loadv2.LoadTask;
 import org.apache.doris.mtmv.MTMVPartitionInfo.MTMVPartitionType;
@@ -194,6 +196,8 @@
 import org.apache.doris.nereids.DorisParser.ShowCreateMTMVContext;
 import org.apache.doris.nereids.DorisParser.ShowCreateProcedureContext;
 import org.apache.doris.nereids.DorisParser.ShowProcedureStatusContext;
+import org.apache.doris.nereids.DorisParser.ShowVariablesContext;
+import org.apache.doris.nereids.DorisParser.ShowViewContext;
 import org.apache.doris.nereids.DorisParser.SimpleColumnDefContext;
 import org.apache.doris.nereids.DorisParser.SimpleColumnDefsContext;
 import org.apache.doris.nereids.DorisParser.SingleStatementContext;
@@ -423,6 +427,8 @@
 import org.apache.doris.nereids.trees.plans.commands.ShowCreateMTMVCommand;
 import org.apache.doris.nereids.trees.plans.commands.ShowCreateProcedureCommand;
 import org.apache.doris.nereids.trees.plans.commands.ShowProcedureStatusCommand;
+import org.apache.doris.nereids.trees.plans.commands.ShowVariablesCommand;
+import org.apache.doris.nereids.trees.plans.commands.ShowViewCommand;
 import org.apache.doris.nereids.trees.plans.commands.UnsetDefaultStorageVaultCommand;
 import org.apache.doris.nereids.trees.plans.commands.UnsetVariableCommand;
 import org.apache.doris.nereids.trees.plans.commands.UnsupportedCommand;
@@ -3999,4 +4005,45 @@ public SetUserPropertiesCommand visitSetUserProperties(SetUserPropertiesContext
     public SetDefaultStorageVaultCommand visitSetDefaultStorageVault(SetDefaultStorageVaultContext ctx) {
         return new SetDefaultStorageVaultCommand(stripQuotes(ctx.identifier().getText()));
     }
+
+    @Override
+    public LogicalPlan visitShowVariables(ShowVariablesContext ctx) {
+        SetType type = SetType.DEFAULT;
+        if (ctx.GLOBAL() != null) {
+            type = SetType.GLOBAL;
+        } else if (ctx.LOCAL() != null || ctx.SESSION() != null) {
+            type = SetType.SESSION;
+        }
+        if (ctx.wildWhere() != null) {
+            if (ctx.wildWhere().LIKE() != null) {
+                return new ShowVariablesCommand(type, stripQuotes(ctx.wildWhere().STRING_LITERAL().getText()));
+            } else {
+                StringBuilder sb = new StringBuilder();
+                sb.append("SELECT `VARIABLE_NAME` AS `Variable_name`, `VARIABLE_VALUE` AS `Value` FROM ");
+                sb.append("`").append(InternalCatalog.INTERNAL_CATALOG_NAME).append("`");
+                sb.append(".");
+                sb.append("`").append(InfoSchemaDb.DATABASE_NAME).append("`");
+                sb.append(".");
+                if (type == SetType.GLOBAL) {
+                    sb.append("`global_variables` ");
+                } else {
+                    sb.append("`session_variables` ");
+                }
+                sb.append(getOriginSql(ctx.wildWhere()));
+                return new NereidsParser().parseSingle(sb.toString());
+            }
+        } else {
+            return new ShowVariablesCommand(type, null);
+        }
+    }
+
+    @Override
+    public ShowViewCommand visitShowView(ShowViewContext ctx) {
+        List<String> tableNameParts = visitMultipartIdentifier(ctx.tableName);
+        String databaseName = null;
+        if (ctx.database != null) {
+            databaseName = stripQuotes(ctx.database.getText());
+        }
+        return new ShowViewCommand(databaseName, new TableNameInfo(tableNameParts));
+    }
 }

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/PlanType.java

@@ -176,5 +176,7 @@ public enum PlanType {
     PREPARED_COMMAND,
     EXECUTE_COMMAND,
     SHOW_CONFIG_COMMAND,
+    SHOW_VARIABLES_COMMAND,
+    SHOW_VIEW_COMMAND,
     REPLAY_COMMAND
 }

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/Command.java

@@ -17,6 +17,8 @@
 
 package org.apache.doris.nereids.trees.plans.commands;
 
+import org.apache.doris.common.Config;
+import org.apache.doris.common.DdlException;
 import org.apache.doris.nereids.memo.GroupExpression;
 import org.apache.doris.nereids.properties.LogicalProperties;
 import org.apache.doris.nereids.trees.expressions.Expression;
@@ -116,4 +118,16 @@ public String treeString() {
     public Plan withGroupExpression(Optional<GroupExpression> groupExpression) {
         throw new RuntimeException("Command do not implement withGroupExpression");
     }
+
+    public void verifyCommandSupported() throws DdlException {
+        // check command has been supported in cloud mode
+        if (Config.isCloudMode()) {
+            checkSupportedInCloudMode();
+        }
+    }
+
+    // check if the command is supported in cloud mode
+    // see checkStmtSupported() in fe/fe-core/src/main/java/org/apache/doris/qe/ShowExecutor.java
+    // override this method if the command is not supported in cloud mode
+    protected void checkSupportedInCloudMode() throws DdlException {}
 }

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/ShowCommand.java

@@ -0,0 +1,53 @@
+// 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.doris.nereids.trees.plans.commands;
+
+import org.apache.doris.analysis.StmtType;
+import org.apache.doris.nereids.trees.plans.PlanType;
+import org.apache.doris.qe.ConnectContext;
+import org.apache.doris.qe.ShowResultSet;
+import org.apache.doris.qe.StmtExecutor;
+
+/**
+ * base class for all show commands
+ */
+public abstract class ShowCommand extends Command implements NoForward {
+    public ShowCommand(PlanType type) {
+        super(type);
+    }
+
+    @Override
+    public StmtType stmtType() {
+        return StmtType.SHOW;
+    }
+
+    @Override
+    public void run(ConnectContext ctx, StmtExecutor executor) throws Exception {
+        ShowResultSet resultSet = doRun(ctx, executor);
+        if (resultSet != null) {
+            if (executor.isProxy()) {
+                executor.setProxyShowResultSet(resultSet);
+            } else {
+                executor.sendResultSet(resultSet);
+            }
+        }
+    }
+
+    public abstract ShowResultSet doRun(ConnectContext ctx, StmtExecutor executor) throws Exception;
+
+}

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/ShowVariablesCommand.java

@@ -0,0 +1,74 @@
+// 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.doris.nereids.trees.plans.commands;
+
+import org.apache.doris.analysis.SetType;
+import org.apache.doris.catalog.Column;
+import org.apache.doris.catalog.ScalarType;
+import org.apache.doris.common.CaseSensibility;
+import org.apache.doris.common.PatternMatcher;
+import org.apache.doris.common.PatternMatcherWrapper;
+import org.apache.doris.nereids.trees.plans.PlanType;
+import org.apache.doris.nereids.trees.plans.visitor.PlanVisitor;
+import org.apache.doris.qe.ConnectContext;
+import org.apache.doris.qe.ShowResultSet;
+import org.apache.doris.qe.ShowResultSetMetaData;
+import org.apache.doris.qe.StmtExecutor;
+import org.apache.doris.qe.VariableMgr;
+
+import java.util.List;
+
+/**
+ * ShowVariablesCommand
+ */
+public class ShowVariablesCommand extends ShowCommand {
+    private static final String NAME_COL = "Variable_name";
+    private static final String VALUE_COL = "Value";
+    private static final String DEFAULT_VALUE_COL = "Default_Value";
+    private static final String CHANGED_COL = "Changed";
+    private static final ShowResultSetMetaData META_DATA = ShowResultSetMetaData.builder()
+            .addColumn(new Column(NAME_COL, ScalarType.createVarchar(20)))
+            .addColumn(new Column(VALUE_COL, ScalarType.createVarchar(20)))
+            .addColumn(new Column(DEFAULT_VALUE_COL, ScalarType.createVarchar(20)))
+            .addColumn(new Column(CHANGED_COL, ScalarType.createVarchar(20)))
+            .build();
+
+    private final SetType type;
+    private final String pattern;
+
+    public ShowVariablesCommand(SetType type, String pattern) {
+        super(PlanType.SHOW_VARIABLES_COMMAND);
+        this.type = type == null ? SetType.DEFAULT : type;
+        this.pattern = pattern;
+    }
+
+    @Override
+    public <R, C> R accept(PlanVisitor<R, C> visitor, C context) {
+        return visitor.visitShowVariablesCommand(this, context);
+    }
+
+    @Override
+    public ShowResultSet doRun(ConnectContext ctx, StmtExecutor executor) throws Exception {
+        PatternMatcher matcher = null;
+        if (pattern != null) {
+            matcher = PatternMatcherWrapper.createMysqlPattern(pattern, CaseSensibility.VARIABLES.getCaseSensibility());
+        }
+        List<List<String>> rows = VariableMgr.dump(type, ctx.getSessionVariable(), matcher);
+        return new ShowResultSet(META_DATA, rows);
+    }
+}