tidb: Fix panic in driverStmt.Query

The prepared statement maybe not query, so the resultset maybe nil.

driver.go

@@ -187,7 +187,7 @@ func newDriverConn(sess *session, d *sqlDriver, schema string) (driver.Conn, err
 
 // Prepare returns a prepared statement, bound to this connection.
 func (c *driverConn) Prepare(query string) (driver.Stmt, error) {
-	stmtID, paramCount, _, err := c.s.PrepareStmt(query)
+	stmtID, paramCount, fields, err := c.s.PrepareStmt(query)
 	if err != nil {
 		return nil, err
 	}
@@ -196,6 +196,7 @@ func (c *driverConn) Prepare(query string) (driver.Stmt, error) {
 		query:      query,
 		stmtID:     stmtID,
 		paramCount: paramCount,
+		isQuery:    fields != nil,
 	}
 	c.stmts[query] = s
 	return s, nil
@@ -460,6 +461,7 @@ type driverStmt struct {
 	query      string
 	stmtID     uint32
 	paramCount int
+	isQuery    bool
 }
 
 // Close closes the statement.
@@ -505,6 +507,14 @@ func (s *driverStmt) Query(args []driver.Value) (driver.Rows, error) {
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
+	if rs == nil {
+		if s.isQuery {
+			return nil, errors.Trace(errNoResult)
+		} else {
+			// The statement is not a query.
+			return nil, nil
+		}
+	}
 	return newdriverRows(rs), nil
 }
 

stmt/stmts/delete.go

@@ -132,7 +132,6 @@ func (s *DeleteStmt) hitWhere(ctx context.Context, t table.Table, data []interfa
 	for _, col := range t.Cols() {
 		m[col.Name.L] = data[col.Offset]
 	}
-
 	ok, err := expressions.EvalBoolExpr(ctx, s.Where, m)
 	if err != nil {
 		return false, errors.Trace(err)

tidb_test.go

@@ -257,6 +257,20 @@ func (s *testMainSuite) TestDriverPrepare(c *C) {
 	mustExec(c, testDB, s.dropDBSQL)
 }
 
+// Testcase for delete panic
+func (s *testMainSuite) TestDeletePanic(c *C) {
+	db, err := sql.Open("tidb", "memory://test")
+	defer db.Close()
+	_, err = db.Exec("create table t (c int)")
+	c.Assert(err, IsNil)
+	_, err = db.Exec("insert into t values (1), (2), (3)")
+	c.Assert(err, IsNil)
+	_, err = db.Query("delete from `t` where `c` = ?", 1)
+	c.Assert(err, IsNil)
+	_, err = db.Query("delete from `t` where `c` = ?", 2)
+	c.Assert(err, IsNil)
+}
+
 func sessionExec(c *C, se Session, sql string) ([]rset.Recordset, error) {
 	se.Execute("BEGIN;")
 	r, err := se.Execute(sql)
@@ -564,6 +578,7 @@ func (s *testSessionSuite) TestSelectForUpdate(c *C) {
 	err = se2.Close()
 	c.Assert(err, IsNil)
 }
+
 func newSession(c *C, store kv.Storage, dbName string) Session {
 	se, err := CreateSession(store)
 	c.Assert(err, IsNil)