[feature](cmd) add UNSET_VARIABLE statement to set back variables

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

@@ -526,6 +526,7 @@ UNINSTALL: 'UNINSTALL';
 UNION: 'UNION';
 UNIQUE: 'UNIQUE';
 UNLOCK: 'UNLOCK';
+UNSET: 'UNSET';
 UNSIGNED: 'UNSIGNED';
 UPDATE: 'UPDATE';
 USE: 'USE';
@@ -534,6 +535,7 @@ USING: 'USING';
 VALUE: 'VALUE';
 VALUES: 'VALUES';
 VARCHAR: 'VARCHAR';
+VARIABLE: 'VARIABLE';
 VARIABLES: 'VARIABLES';
 VERBOSE: 'VERBOSE';
 VERSION: 'VERSION';

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

@@ -833,9 +833,11 @@ nonReserved
     | TYPES
     | UNCOMMITTED
     | UNLOCK
+    | UNSET
     | USER
     | VALUE
     | VARCHAR
+    | VARIABLE
     | VARIABLES
     | VERBOSE
     | VERSION

fe/fe-core/src/main/cup/sql_parser.cup

@@ -623,6 +623,7 @@ terminal String
     KW_UNION,
     KW_UNIQUE,
     KW_UNLOCK,
+    KW_UNSET,
     KW_UNSIGNED,
     KW_UPDATE,
     KW_USE,
@@ -631,6 +632,7 @@ terminal String
     KW_VALUE,
     KW_VALUES,
     KW_VARCHAR,
+    KW_VARIABLE,
     KW_VARIABLES,
     KW_VERBOSE,
     KW_VERSION,
@@ -675,7 +677,7 @@ nonterminal List<StatementBase> stmts;
 nonterminal StatementBase stmt, show_stmt, show_param, help_stmt, load_stmt,
     create_routine_load_stmt, pause_routine_load_stmt, resume_routine_load_stmt, stop_routine_load_stmt,
     show_routine_load_stmt, show_routine_load_task_stmt, show_create_routine_load_stmt, show_create_load_stmt, show_create_reporitory_stmt,
-    describe_stmt, alter_stmt,
+    describe_stmt, alter_stmt, unset_var_stmt,
     use_stmt, kill_stmt, drop_stmt, recover_stmt, grant_stmt, revoke_stmt, create_stmt, set_stmt, sync_stmt, cancel_stmt, cancel_param, delete_stmt,
     switch_stmt, transaction_stmt, unsupported_stmt, export_stmt, admin_stmt, truncate_stmt,
     import_columns_stmt, import_delete_on_stmt, import_sequence_stmt, import_where_stmt, install_plugin_stmt, uninstall_plugin_stmt,
@@ -1105,6 +1107,8 @@ stmt ::=
     {: RESULT = use; :}
     | set_stmt:set
     {: RESULT = set; :}
+    | unset_var_stmt:stmt
+    {: RESULT = stmt; :}
     | kill_stmt:kill
     {: RESULT = kill; :}
     | kill_analysis_job_stmt: k
@@ -5006,6 +5010,18 @@ set_stmt ::=
     :}
     ;
 
+// Unset variable statement
+unset_var_stmt ::=
+    KW_UNSET opt_var_type:type KW_VARIABLE variable_name:variable
+    {:
+        RESULT = new UnsetVariableStmt(type, variable);
+    :}
+    | KW_UNSET opt_var_type:type KW_VARIABLE KW_ALL
+    {:
+        RESULT = new UnsetVariableStmt(type, true);
+    :}
+    ;
+
 user_property_list ::=
     user_property:property
     {:
@@ -7757,6 +7773,8 @@ keyword ::=
     {: RESULT = id; :}
     | KW_USER:id
     {: RESULT = id; :}
+    | KW_VARIABLE:id
+    {: RESULT = id; :}
     | KW_VARIABLES:id
     {: RESULT = id; :}
     | KW_VALUE:id
@@ -7793,6 +7811,8 @@ keyword ::=
     {: RESULT = id; :}
     | KW_FREE:id
     {: RESULT = id; :}
+    | KW_UNSET:id
+    {: RESULT = id; :}
     | KW_TASK:id
     {: RESULT = id; :}
     | KW_ROUTINE:id

fe/fe-core/src/main/java/org/apache/doris/analysis/UnsetVariableStmt.java

@@ -0,0 +1,97 @@
+// 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.analysis;
+
+import org.apache.doris.common.AnalysisException;
+import org.apache.doris.common.UserException;
+
+import com.amazonaws.util.StringUtils;
+
+// Unset variables statement
+public class UnsetVariableStmt extends StatementBase {
+    private SetType setType;
+
+    // variables to restore
+    private String variable = null;
+
+    private boolean applyToAll = false;
+
+    public UnsetVariableStmt(SetType setType, String varName) {
+        this.setType = setType;
+        this.variable = varName;
+    }
+
+    public UnsetVariableStmt(SetType setType, boolean applyToAll) {
+        this.setType = setType;
+        this.applyToAll = applyToAll;
+    }
+
+    public SetType getSetType() {
+        return setType;
+    }
+
+    public String getVariable() {
+        return variable;
+    }
+
+    public boolean isApplyToAll() {
+        return applyToAll;
+    }
+
+    // change type global to session avoid to write in non-master node.
+    public void modifySetVarsForExecute() {
+        if (setType == SetType.GLOBAL) {
+            setType = SetType.SESSION;
+        }
+    }
+
+    @Override
+    public void analyze(Analyzer analyzer) throws UserException {
+        if (StringUtils.isNullOrEmpty(variable) && !applyToAll) {
+            throw new AnalysisException("You should specific the unset variable.");
+        }
+    }
+
+    @Override
+    public String toSql() {
+        StringBuilder sb = new StringBuilder();
+
+        sb.append("UNSET ");
+        sb.append(setType).append(" VARIABLE ");
+        if (!StringUtils.isNullOrEmpty(variable)) {
+            sb.append(variable).append(" ");
+        } else if (applyToAll) {
+            sb.append("ALL");
+        }
+        return sb.toString();
+    }
+
+    @Override
+    public String toString() {
+        return toSql();
+    }
+
+    @Override
+    public RedirectStatus getRedirectStatus() {
+        if (setType == SetType.GLOBAL) {
+            return RedirectStatus.FORWARD_WITH_SYNC;
+        }
+
+        return RedirectStatus.NO_FORWARD;
+    }
+}

fe/fe-core/src/main/java/org/apache/doris/qe/StmtExecutor.java

@@ -56,7 +56,9 @@
 import org.apache.doris.analysis.SelectStmt;
 import org.apache.doris.analysis.SetOperationStmt;
 import org.apache.doris.analysis.SetStmt;
+import org.apache.doris.analysis.SetType;
 import org.apache.doris.analysis.SetVar;
+import org.apache.doris.analysis.SetVar.SetVarType;
 import org.apache.doris.analysis.ShowStmt;
 import org.apache.doris.analysis.SqlParser;
 import org.apache.doris.analysis.SqlScanner;
@@ -73,6 +75,7 @@
 import org.apache.doris.analysis.TransactionStmt;
 import org.apache.doris.analysis.UnifiedLoadStmt;
 import org.apache.doris.analysis.UnlockTablesStmt;
+import org.apache.doris.analysis.UnsetVariableStmt;
 import org.apache.doris.analysis.UnsupportedStmt;
 import org.apache.doris.analysis.UpdateStmt;
 import org.apache.doris.analysis.UseStmt;
@@ -773,6 +776,8 @@ public void executeByLegacy(TUniqueId queryId) throws Exception {
                 handleQueryWithRetry(queryId);
             } else if (parsedStmt instanceof SetStmt) {
                 handleSetStmt();
+            } else if (parsedStmt instanceof UnsetVariableStmt) {
+                handleUnsetVariableStmt();
             } else if (parsedStmt instanceof SwitchStmt) {
                 handleSwitchStmt();
             } else if (parsedStmt instanceof UseStmt) {
@@ -918,6 +923,19 @@ private void forwardToMaster() throws Exception {
             for (SetVar var : setStmt.getSetVars()) {
                 VariableMgr.setVarForNonMasterFE(context.getSessionVariable(), var);
             }
+        } else if (parsedStmt instanceof UnsetVariableStmt) {
+            UnsetVariableStmt unsetStmt = (UnsetVariableStmt) parsedStmt;
+            if (unsetStmt.isApplyToAll()) {
+                VariableMgr.setAllVarsToDefaultValue(context.getSessionVariable(), SetType.SESSION);
+            } else {
+                String defaultValue = VariableMgr.getDefaultValue(unsetStmt.getVariable());
+                if (defaultValue == null) {
+                    ErrorReport.reportDdlException(ErrorCode.ERR_UNKNOWN_SYSTEM_VARIABLE, unsetStmt.getVariable());
+                }
+                SetVar var = new SetVar(SetType.SESSION, unsetStmt.getVariable(),
+                        new StringLiteral(defaultValue), SetVarType.SET_SESSION_VAR);
+                VariableMgr.setVar(context.getSessionVariable(), var);
+            }
         }
     }
 
@@ -1302,6 +1320,30 @@ private void handleSetStmt() {
         context.getState().setOk();
     }
 
+    // Process unset variable statement.
+    private void handleUnsetVariableStmt() {
+        try {
+            UnsetVariableStmt unsetStmt = (UnsetVariableStmt) parsedStmt;
+            if (unsetStmt.isApplyToAll()) {
+                VariableMgr.setAllVarsToDefaultValue(context.getSessionVariable(), unsetStmt.getSetType());
+            } else {
+                String defaultValue = VariableMgr.getDefaultValue(unsetStmt.getVariable());
+                if (defaultValue == null) {
+                    ErrorReport.reportDdlException(ErrorCode.ERR_UNKNOWN_SYSTEM_VARIABLE, unsetStmt.getVariable());
+                }
+                SetVar var = new SetVar(unsetStmt.getSetType(), unsetStmt.getVariable(),
+                        new StringLiteral(defaultValue), SetVarType.SET_SESSION_VAR);
+                VariableMgr.setVar(context.getSessionVariable(), var);
+            }
+        } catch (DdlException e) {
+            LOG.warn("", e);
+            // Return error message to client.
+            context.getState().setError(ErrorCode.ERR_LOCAL_VARIABLE, e.getMessage());
+            return;
+        }
+        context.getState().setOk();
+    }
+
     // send values from cache.
     // return true if the meta fields has been sent, otherwise, return false.
     // the meta fields must be sent right before the first batch of data(or eos flag).

fe/fe-core/src/main/java/org/apache/doris/qe/VariableMgr.java

@@ -20,6 +20,8 @@
 import org.apache.doris.analysis.LiteralExpr;
 import org.apache.doris.analysis.SetType;
 import org.apache.doris.analysis.SetVar;
+import org.apache.doris.analysis.SetVar.SetVarType;
+import org.apache.doris.analysis.StringLiteral;
 import org.apache.doris.analysis.VariableExpr;
 import org.apache.doris.catalog.Env;
 import org.apache.doris.catalog.Type;
@@ -651,6 +653,27 @@ private static ImmutableMap<String, VarContext> getDisplaySessionVars() {
         return ImmutableMap.copyOf(result);
     }
 
+    public static void setAllVarsToDefaultValue(SessionVariable sessionVariable, SetType setType)
+            throws DdlException {
+        for (Map.Entry<String, VarContext> entry : ctxByDisplayVarName.entrySet()) {
+            VarContext varCtx = entry.getValue();
+            SetVar setVar = new SetVar(setType, entry.getKey(),
+                    new StringLiteral(varCtx.defaultValue), SetVarType.SET_SESSION_VAR);
+            try {
+                checkUpdate(setVar, varCtx.getFlag());
+            } catch (DdlException e) {
+                LOG.debug("no need to set var for non master fe: {}", setVar.getVariable(), e);
+                continue;
+            }
+            setVarInternal(sessionVariable, setVar, varCtx);
+        }
+    }
+
+    public static String getDefaultValue(String key) {
+        VarContext varContext = ctxByDisplayVarName.get(key);
+        return varContext == null ? null : varContext.defaultValue;
+    }
+
     // Dump all fields. Used for `show variables`
     public static List<List<String>> dump(SetType type, SessionVariable sessionVar, PatternMatcher matcher) {
         List<List<String>> rows = Lists.newArrayList();

fe/fe-core/src/main/jflex/sql_scanner.flex

@@ -506,6 +506,8 @@ import org.apache.doris.qe.SqlModeHelper;
         keywordMap.put("ignore", new Integer(SqlParserSymbols.KW_IGNORE));
         keywordMap.put("expired", new Integer(SqlParserSymbols.KW_EXPIRED));
         keywordMap.put("convert_light_schema_change_process", new Integer(SqlParserSymbols.KW_CONVERT_LSC));
+        keywordMap.put("unset", new Integer(SqlParserSymbols.KW_UNSET));
+        keywordMap.put("variable", new Integer(SqlParserSymbols.KW_VARIABLE));
    }
 
   // map from token id to token description