Update yacc_sql.y (#595)

Fix memory leak of token when bison failed to parse SQL.
Use left recursion for better performance and remove vector reverse.

### What problem were solved in this pull request?
When bison fails to parse SQL, memory leaks may occur, such as
select * from t where id><1;

Issue Number: close #308

Problem:

### What is changed and how it works?
In yacc_sql.y, use %destructor to specify the memory release action that
needs to be called when parsing fails for the token, in order to prevent
memory leaks that may occur in the event of an error.

### Other information

Author: evtrouble

src/observer/sql/parser/yacc_sql.y

@@ -136,6 +136,19 @@ UnboundAggregateExpr *create_aggregate_expression(const char *aggregate_name,
   float                                      floats;
 }
 
+%destructor { delete $$; } <condition>
+%destructor { delete $$; } <value>
+%destructor { delete $$; } <rel_attr>
+%destructor { delete $$; } <attr_infos>
+%destructor { delete $$; } <attr_info>
+%destructor { delete $$; } <expression>
+%destructor { delete $$; } <expression_list>
+%destructor { delete $$; } <value_list>
+%destructor { delete $$; } <condition_list>
+// %destructor { delete $$; } <rel_attr_list>
+%destructor { delete $$; } <relation_list>
+%destructor { delete $$; } <key_list>
+
 %token <number> NUMBER
 %token <floats> FLOAT
 %token <cstring> ID
@@ -304,45 +317,37 @@ drop_index_stmt:      /*drop index 语句的语法解析树*/
     }
     ;
 create_table_stmt:    /*create table 语句的语法解析树*/
-    CREATE TABLE ID LBRACE attr_def attr_def_list primary_key RBRACE storage_format
+    CREATE TABLE ID LBRACE attr_def_list primary_key RBRACE storage_format
     {
       $$ = new ParsedSqlNode(SCF_CREATE_TABLE);
       CreateTableSqlNode &create_table = $$->create_table;
       create_table.relation_name = $3;
       //free($3);
 
-      vector<AttrInfoSqlNode> *src_attrs = $6;
-
-      if (src_attrs != nullptr) {
-        create_table.attr_infos.swap(*src_attrs);
-        delete src_attrs;
-      }
-      create_table.attr_infos.emplace_back(*$5);
-      reverse(create_table.attr_infos.begin(), create_table.attr_infos.end());
+      create_table.attr_infos.swap(*$5);
       delete $5;
-      if ($7 != nullptr) {
-        create_table.primary_keys.swap(*$7);
-        delete $7;
+
+      if ($6 != nullptr) {
+        create_table.primary_keys.swap(*$6);
+        delete $6;
       }
-      if ($9 != nullptr) {
-        create_table.storage_format = $9;
+      if ($8 != nullptr) {
+        create_table.storage_format = $8;
       }
     }
     ;
 
 attr_def_list:
-    /* empty */
+    attr_def
     {
-      $$ = nullptr;
+      $$ = new vector<AttrInfoSqlNode>;
+      $$->emplace_back(*$1);
+      delete $1;
     }
     | attr_def_list COMMA attr_def
     {
-      if ($1 != nullptr) {
-        $$ = $1;
-      } else {
-        $$ = new vector<AttrInfoSqlNode>;
-      }
-      $$->insert($$->begin(), *$3);
+      $$ = $1;
+      $$->emplace_back(*$3);
       delete $3;
     }
     ;
@@ -400,33 +405,26 @@ attr_list:
     ;
 
 insert_stmt:        /*insert   语句的语法解析树*/
-    INSERT INTO ID VALUES LBRACE value value_list RBRACE 
+    INSERT INTO ID VALUES LBRACE value_list RBRACE 
     {
       $$ = new ParsedSqlNode(SCF_INSERT);
       $$->insertion.relation_name = $3;
-      if ($7 != nullptr) {
-        $$->insertion.values.swap(*$7);
-        delete $7;
-      }
-      $$->insertion.values.emplace_back(*$6);
-      reverse($$->insertion.values.begin(), $$->insertion.values.end());
+      $$->insertion.values.swap(*$6);
       delete $6;
     }
     ;
 
 value_list:
-    /* empty */
+    value
     {
-      $$ = nullptr;
+      $$ = new vector<Value>;
+      $$->emplace_back(*$1);
+      delete $1;
     }
-    | COMMA value value_list  { 
-      if ($3 != nullptr) {
-        $$ = $3;
-      } else {
-        $$ = new vector<Value>;
-      }
-      $$->emplace_back(*$2);
-      delete $2;
+    | value_list COMMA value { 
+      $$ = $1;
+      $$->emplace_back(*$3);
+      delete $3;
     }
     ;
 value: