Only rewrite database() against dual

Signed-off-by: Andres Taylor <andres@planetscale.com>

go/vt/sqlparser/expression_rewriting.go

@@ -32,6 +32,7 @@ func PrepareAST(in Statement, bindVars map[string]*querypb.BindVariable, prefix
 // RewriteAST rewrites the whole AST, replacing function calls and adding column aliases to queries
 func RewriteAST(in Statement) (*RewriteASTResult, error) {
 	er := new(expressionRewriter)
+	er.shouldRewriteDatabaseFunc = shouldRewriteDatabaseFunc(in)
 	Rewrite(in, er.goingDown, nil)
 
 	return &RewriteASTResult{
@@ -41,6 +42,25 @@ func RewriteAST(in Statement) (*RewriteASTResult, error) {
 	}, nil
 }
 
+func shouldRewriteDatabaseFunc(in Statement) bool {
+	selct, ok := in.(*Select)
+	if !ok {
+		return false
+	}
+	if len(selct.From) != 1 {
+		return false
+	}
+	aliasedTable, ok := selct.From[0].(*AliasedTableExpr)
+	if !ok {
+		return false
+	}
+	tableName, ok := aliasedTable.Expr.(TableName)
+	if !ok {
+		return false
+	}
+	return tableName.Name.String() == "dual"
+}
+
 // RewriteASTResult contains the rewritten ast and meta information about it
 type RewriteASTResult struct {
 	AST              Statement
@@ -49,8 +69,9 @@ type RewriteASTResult struct {
 }
 
 type expressionRewriter struct {
-	lastInsertID, database bool
-	err                    error
+	lastInsertID, database    bool
+	shouldRewriteDatabaseFunc bool
+	err                       error
 }
 
 const (
@@ -67,6 +88,7 @@ func (er *expressionRewriter) goingDown(cursor *Cursor) bool {
 			buf := NewTrackedBuffer(nil)
 			node.Expr.Format(buf)
 			inner := new(expressionRewriter)
+			inner.shouldRewriteDatabaseFunc = er.shouldRewriteDatabaseFunc
 			tmp := Rewrite(node.Expr, inner.goingDown, nil)
 			newExpr, ok := tmp.(Expr)
 			if !ok {
@@ -91,7 +113,7 @@ func (er *expressionRewriter) goingDown(cursor *Cursor) bool {
 				cursor.Replace(bindVarExpression(LastInsertIDName))
 				er.lastInsertID = true
 			}
-		case node.Name.EqualString("database"):
+		case node.Name.EqualString("database") && er.shouldRewriteDatabaseFunc:
 			if len(node.Exprs) > 0 {
 				er.err = vterrors.New(vtrpc.Code_INVALID_ARGUMENT, "Syntax error. DATABASE() takes no arguments")
 			} else {

go/vt/sqlparser/expression_rewriting_test.go

@@ -55,14 +55,19 @@ func TestRewrites(in *testing.T) {
 			db:       true, liid: true,
 		},
 		{
-			in:       "select (select database() from test) from test",
-			expected: "select (select :__vtdbname as `database()` from test) as `(select database() from test)` from test",
+			in:       "select (select database() from dual) from dual",
+			expected: "select (select :__vtdbname as `database()` from dual) as `(select database() from dual)` from dual",
 			db:       true, liid: false,
 		},
 		{
 			in:       "select id from user where database()",
-			expected: "select id from user where :__vtdbname",
-			db:       true, liid: false,
+			expected: "select id from user where database()",
+			db:       false, liid: false,
+		},
+		{
+			in:       "select table_name from information_schema.tables where table_schema = database()",
+			expected: "select table_name from information_schema.tables where table_schema = database()",
+			db:       false, liid: false,
 		},
 	}
 
@@ -77,16 +82,10 @@ func TestRewrites(in *testing.T) {
 			expected, err := Parse(tc.expected)
 			require.NoError(t, err)
 
-			s := toString(expected)
-			require.Equal(t, s, toString(result.AST))
+			s := String(expected)
+			require.Equal(t, s, String(result.AST))
 			require.Equal(t, tc.liid, result.NeedLastInsertID, "should need last insert id")
 			require.Equal(t, tc.db, result.NeedDatabase, "should need database name")
 		})
 	}
 }
-
-func toString(node SQLNode) string {
-	buf := NewTrackedBuffer(nil)
-	node.Format(buf)
-	return buf.String()
-}

go/vt/vtgate/executor.go

@@ -282,7 +282,6 @@ func (e *Executor) handleExec(ctx context.Context, safeSession *SafeSession, sql
 			sql = comments.Leading + normalized + comments.Trailing
 			if rewriteResult.NeedDatabase {
 				keyspace, _, _, _ := e.ParseDestinationTarget(safeSession.TargetString)
-				log.Warningf("This is the keyspace name: ---> %v", keyspace)
 				if keyspace == "" {
 					bindVars[sqlparser.DBVarName] = sqltypes.NullBindVariable
 				} else {