Support identifiers starting with digits in lexer

ClickHouse allows identifiers like '1alias1name1' as aliases after AS.
The lexer now recognizes these as identifiers rather than treating the
leading digits as a NUMBER token followed by an IDENT token.

The change adds a check in readNumberOrIdent to detect when digits are
directly followed by letters (excluding exponent notation like 1e5 and
base prefixes like 0x, 0b, 0o).

Author: claude

lexer/lexer.go

@@ -766,6 +766,22 @@ func (l *Lexer) readNumberOrIdent() Item {
 		}
 	}
 
+	// Check if directly followed by letter (identifier like 1alias1name1)
+	// Exclude exponent (e/E followed by digit/+/-) and base prefixes (0x, 0b, 0o)
+	if unicode.IsLetter(l.ch) {
+		val := sb.String()
+		isExponent := (l.ch == 'e' || l.ch == 'E') && (unicode.IsDigit(l.peekChar()) || l.peekChar() == '+' || l.peekChar() == '-')
+		isBasePrefix := val == "0" && (l.ch == 'x' || l.ch == 'X' || l.ch == 'b' || l.ch == 'B' || l.ch == 'o' || l.ch == 'O')
+		if !isExponent && !isBasePrefix {
+			// This is an identifier that starts with digits (e.g., 1alias1name1)
+			for isIdentChar(l.ch) {
+				sb.WriteRune(l.ch)
+				l.readChar()
+			}
+			return Item{Token: token.IDENT, Value: sb.String(), Pos: pos}
+		}
+	}
+
 	// Not an identifier, continue as number
 	// But we already consumed the digits, so continue from here
 	// Handle underscore separators in numbers (only if followed by a digit)

parser/testdata/01460_allow_dollar_and_number_in_identifier/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt2": true
-  }
-}
+{}