Fix parsing of quoted identifiers in SHOW CREATE TABLE queries

sql/parse/parse_test.go

@@ -1007,9 +1007,15 @@ var fixtures = map[string]sql.Node{
 		),
 		plan.NewShowCollation(),
 	),
-	`ROLLBACK`:                           plan.NewRollback(),
-	"SHOW CREATE TABLE `mytable`":        plan.NewShowCreateTable("", nil, "mytable"),
-	"SHOW CREATE TABLE `mydb`.`mytable`": plan.NewShowCreateTable("mydb", nil, "mytable"),
+	`ROLLBACK`:                               plan.NewRollback(),
+	"SHOW CREATE TABLE `mytable`":            plan.NewShowCreateTable("", nil, "mytable"),
+	"SHOW CREATE TABLE `mydb`.`mytable`":     plan.NewShowCreateTable("mydb", nil, "mytable"),
+	"SHOW CREATE TABLE `my.table`":           plan.NewShowCreateTable("", nil, "my.table"),
+	"SHOW CREATE TABLE `my.db`.`my.table`":   plan.NewShowCreateTable("my.db", nil, "my.table"),
+	"SHOW CREATE TABLE `my``table`":          plan.NewShowCreateTable("", nil, "my`table"),
+	"SHOW CREATE TABLE `my``db`.`my``table`": plan.NewShowCreateTable("my`db", nil, "my`table"),
+	"SHOW CREATE TABLE ````":                 plan.NewShowCreateTable("", nil, "`"),
+	"SHOW CREATE TABLE `.`":                  plan.NewShowCreateTable("", nil, "."),
 	`SELECT '2018-05-01' + INTERVAL 1 DAY`: plan.NewProject(
 		[]sql.Expression{expression.NewArithmetic(
 			expression.NewLiteral("2018-05-01", sql.Text),

sql/parse/util.go

@@ -144,6 +144,36 @@ func readValidIdentRune(r *bufio.Reader, buf *bytes.Buffer) error {
 	return nil
 }
 
+func readValidQuotedIdentRune(r *bufio.Reader, buf *bytes.Buffer) error {
+	bs, err := r.Peek(2)
+	if err != nil {
+		return err
+	}
+
+	if bs[0] == '`' && bs[1] == '`' {
+		if _, _, err := r.ReadRune(); err != nil {
+			return err
+		}
+		if _, _, err := r.ReadRune(); err != nil {
+			return err
+		}
+		buf.WriteRune('`')
+		return nil
+	}
+
+	if bs[0] == '`' && bs[1] != '`' {
+		return io.EOF
+	}
+
+	if _, _, err := r.ReadRune(); err != nil {
+		return err
+	}
+
+	buf.WriteByte(bs[0])
+
+	return nil
+}
+
 func unreadString(r *bufio.Reader, str string) {
 	nr := *r
 	r.Reset(io.MultiReader(strings.NewReader(str), &nr))
@@ -169,6 +199,26 @@ func readIdent(ident *string) parseFunc {
 	}
 }
 
+func readQuotedIdent(ident *string) parseFunc {
+	return func(r *bufio.Reader) error {
+		var buf bytes.Buffer
+		if err := readValidQuotedIdentRune(r, &buf); err != nil {
+			return err
+		}
+
+		for {
+			if err := readValidQuotedIdentRune(r, &buf); err == io.EOF {
+				break
+			} else if err != nil {
+				return err
+			}
+		}
+
+		*ident = strings.ToLower(buf.String())
+		return nil
+	}
+}
+
 func oneOf(options ...string) parseFunc {
 	return func(r *bufio.Reader) error {
 		var ident string
@@ -235,7 +285,7 @@ func readQuotableIdent(ident *string) parseFunc {
 		if nextChar[0] == '`' {
 			steps = parseFuncs{
 				expectQuote,
-				readIdent(ident),
+				readQuotedIdent(ident),
 				expectQuote,
 			}
 		} else {