Cover single statements in skipped SQL tails

Verify that EXPLAIN and CREATE INDEX containing quoted semicolons each
retain one original statement. Consumers enforcing one statement per
query pattern must not mistake these inputs for batches.

Author: laodouya

parse_test.go

@@ -785,6 +785,34 @@ func TestFloatColumnPrecisionSemicolonDefault(t *testing.T) {
 	}
 }
 
+func TestSkippedTailSingleStatements(t *testing.T) {
+	for _, input := range []string{
+		"EXPLAIN SELECT 'a;select 2 --'",
+		"create index i on t(a) where a = 'x;select 2 --'",
+	} {
+		t.Run(input, func(t *testing.T) {
+			if _, err := Parse(input); err != nil {
+				t.Fatal(err)
+			}
+			queries, statements, err := ParseMultiple(NewStringTokenizer(input))
+			if err != nil || len(queries) != 1 || len(statements) != 1 || queries[0] != input {
+				t.Fatalf("want one unchanged statement: %v, %v, %v", queries, statements, err)
+			}
+			for _, tokenizer := range []*Tokenizer{NewStringTokenizer(input), NewTokenizer(strings.NewReader(input))} {
+				if _, err := ParseNext(tokenizer); err != nil {
+					t.Fatal(err)
+				}
+				if tokenizer.Position != len(input)+1 {
+					t.Errorf("stopped at %d, want EOF at %d", tokenizer.Position, len(input)+1)
+				}
+				if _, err := ParseNext(tokenizer); err != io.EOF {
+					t.Errorf("after single statement: %v, want EOF", err)
+				}
+			}
+		})
+	}
+}
+
 func TestDDLTailSemicolons(t *testing.T) {
 	for _, prefix := range []string{"create index i on t(", "create table t (列 text check ("} {
 		for _, expression := range []string{