fix drop view bug and keyword 'account' (#4725)

Approved by: @aunjgr, @aressu1985, @ouyuanning

pkg/sql/parsers/dialect/mysql/mysql_sql.y

@@ -6819,8 +6819,7 @@ reserved_table_id:
 |   reserved_keyword
 
 reserved_keyword:
-    ACCOUNT
-|   ADD
+    ADD
 |   ALL
 |   AND
 |   AS
@@ -6982,7 +6981,8 @@ reserved_keyword:
 |   SECONDARY
 
 non_reserved_keyword:
-    AGAINST
+    ACCOUNT
+|   AGAINST
 |   AVG_ROW_LENGTH
 |   AUTO_RANDOM
 |   ACTION

pkg/sql/plan/build_ddl.go

@@ -388,8 +388,12 @@ func buildDropTable(stmt *tree.DropTable, ctx CompilerContext) (*Plan, error) {
 				break
 			}
 		}
-		if isView {
+		if isView && !dropTable.IfExists {
+			// drop table v0, v0 is view
 			return nil, errors.New("", fmt.Sprintf("table %s is not exists", dropTable.Table))
+		} else if isView {
+			// drop table if exists v0, v0 is view
+			dropTable.Table = ""
 		}
 	}
 

test/cases/table/create_table.test

@@ -13,4 +13,5 @@ create table table16 (1a20 int,1e int);
 create table $table18 (a$1 int, $b int, c$ int);
 create table table19$ (a int);
 create table table17 (`index` int);
+create table account(a int);
 show tables;

test/cases/view/view.test

@@ -23,4 +23,10 @@ create view v2 as select 'a';
 show create view v2;
 show create table v2;
 drop view v1;
-drop view v2;
\ No newline at end of file
+drop view v2;
+
+create table tt(a int);
+create view vv as select * from tt;
+drop table if exists tt;
+drop table if exists vv;
+drop view vv;
\ No newline at end of file

test/result/table/create_table.result

@@ -13,6 +13,7 @@ create table table16 (1a20 int,1e int);
 create table $table18 (a$1 int, $b int, c$ int);
 create table table19$ (a int);
 create table table17 (`index` int);
+create table account(a int);
 show tables;
 tables_in_create_table
 table01
@@ -30,3 +31,4 @@ table16
 $table18
 table19$
 table17
+account

test/result/view/view.result

@@ -41,4 +41,10 @@ show create table v2;
 View    Create View
 v2    create view v2 as select 'a';
 drop view v1;
-drop view v2;
\ No newline at end of file
+drop view v2;
+
+create table tt(a int);
+create view vv as select * from tt;
+drop table if exists tt;
+drop table if exists vv;
+drop view vv;
\ No newline at end of file