Add Cloud Spanner style read only transaction

ast/dml.go

@@ -2629,3 +2629,18 @@ func (m FulltextSearchModifier) IsNaturalLanguageMode() bool {
 func (m FulltextSearchModifier) WithQueryExpansion() bool {
 	return m&FulltextSearchModifierWithQueryExpansion == FulltextSearchModifierWithQueryExpansion
 }
+
+type TimestampBound struct {
+	Mode      TimestampBoundMode
+	Timestamp ExprNode
+}
+
+type TimestampBoundMode int
+
+const (
+	TimestampBoundStrong TimestampBoundMode = iota
+	TimestampBoundMaxStaleness
+	TimestampBoundExactStaleness
+	TimestampBoundReadTimestamp
+	TimestampBoundMinReadTimestamp
+)

ast/expressions.go

@@ -1339,6 +1339,7 @@ func (n *MatchAgainst) Accept(v Visitor) (Node, bool) {
 	if skipChildren {
 		return v.Leave(newNode)
 	}
+	n = newNode.(*MatchAgainst)
 	for i, colName := range n.ColumnNames {
 		newColName, ok := colName.Accept(v)
 		if !ok {

ast/misc.go

@@ -377,13 +377,37 @@ func (n *ExecuteStmt) Accept(v Visitor) (Node, bool) {
 // See https://dev.mysql.com/doc/refman/5.7/en/commit.html
 type BeginStmt struct {
 	stmtNode
-	Mode string
+	Mode     string
+	ReadOnly bool
+	Bound    *TimestampBound
 }
 
 // Restore implements Node interface.
 func (n *BeginStmt) Restore(ctx *RestoreCtx) error {
 	if n.Mode == "" {
-		ctx.WriteKeyWord("START TRANSACTION")
+		if n.ReadOnly {
+			ctx.WriteKeyWord("START TRANSACTION READ ONLY")
+			if n.Bound != nil {
+				switch n.Bound.Mode {
+				case TimestampBoundStrong:
+					ctx.WriteKeyWord(" WITH TIMESTAMP BOUND STRONG")
+				case TimestampBoundMaxStaleness:
+					ctx.WriteKeyWord(" WITH TIMESTAMP BOUND MAX STALENESS ")
+					return n.Bound.Timestamp.Restore(ctx)
+				case TimestampBoundExactStaleness:
+					ctx.WriteKeyWord(" WITH TIMESTAMP BOUND EXACT STALENESS ")
+					return n.Bound.Timestamp.Restore(ctx)
+				case TimestampBoundReadTimestamp:
+					ctx.WriteKeyWord(" WITH TIMESTAMP BOUND READ TIMESTAMP ")
+					return n.Bound.Timestamp.Restore(ctx)
+				case TimestampBoundMinReadTimestamp:
+					ctx.WriteKeyWord(" WITH TIMESTAMP BOUND MIN READ TIMESTAMP ")
+					return n.Bound.Timestamp.Restore(ctx)
+				}
+			}
+		} else {
+			ctx.WriteKeyWord("START TRANSACTION")
+		}
 	} else {
 		ctx.WriteKeyWord("BEGIN ")
 		ctx.WriteKeyWord(n.Mode)
@@ -398,6 +422,13 @@ func (n *BeginStmt) Accept(v Visitor) (Node, bool) {
 		return v.Leave(newNode)
 	}
 	n = newNode.(*BeginStmt)
+	if n.Bound != nil && n.Bound.Timestamp != nil {
+		newTimestamp, ok := n.Bound.Timestamp.Accept(v)
+		if !ok {
+			return n, false
+		}
+		n.Bound.Timestamp = newTimestamp.(ExprNode)
+	}
 	return v.Leave(n)
 }
 

misc.go

@@ -169,6 +169,7 @@ var tokenMap = map[string]int{
 	"BOOL":                     boolType,
 	"BOOLEAN":                  booleanType,
 	"BOTH":                     both,
+	"BOUND":                    bound,
 	"BTREE":                    btree,
 	"BUCKETS":                  buckets,
 	"BUILTINS":                 builtins,
@@ -270,6 +271,7 @@ var tokenMap = map[string]int{
 	"ESCAPED":                  escaped,
 	"EVENT":                    event,
 	"EVENTS":                   events,
+	"EXACT":                    exact,
 	"EXCLUSIVE":                exclusive,
 	"EXCEPT":                   except,
 	"EXCHANGE":                 exchange,
@@ -549,6 +551,7 @@ var tokenMap = map[string]int{
 	"SQL_TSI_YEAR":             sqlTsiYear,
 	"SOURCE":                   source,
 	"SSL":                      ssl,
+	"STALENESS":                staleness,
 	"START":                    start,
 	"STARTING":                 starting,
 	"STATS":                    stats,
@@ -572,6 +575,7 @@ var tokenMap = map[string]int{
 	"STORED":                   stored,
 	"STRAIGHT_JOIN":            straightJoin,
 	"STREAM_AGG":               hintSTREAMAGG,
+	"STRONG":                   strong,
 	"SUBDATE":                  subDate,
 	"SUBJECT":                  subject,
 	"SUBPARTITION":             subpartition,