Add COMMENT keyword for SQL COMMENT COLUMN clauses

Rename the special COMMENT token (for line comments like -- and /* */)
to LINE_COMMENT to avoid collision with the COMMENT SQL keyword needed
for ALTER TABLE COMMENT COLUMN and similar statements.

Author: claude

lexer/lexer.go

@@ -306,7 +306,7 @@ func (l *Lexer) readLineComment() Item {
 	}
 	// Strip trailing semicolon from comment - it's a statement terminator, not part of comment
 	text := strings.TrimRight(sb.String(), ";")
-	return Item{Token: token.COMMENT, Value: text, Pos: pos}
+	return Item{Token: token.LINE_COMMENT, Value: text, Pos: pos}
 }
 
 func (l *Lexer) readHashComment() Item {
@@ -322,7 +322,7 @@ func (l *Lexer) readHashComment() Item {
 	}
 	// Strip trailing semicolon from comment - it's a statement terminator, not part of comment
 	text := strings.TrimRight(sb.String(), ";")
-	return Item{Token: token.COMMENT, Value: text, Pos: pos}
+	return Item{Token: token.LINE_COMMENT, Value: text, Pos: pos}
 }
 
 // readUnicodeMinusComment reads from a unicode minus (U+2212) to the end of line or semicolon.
@@ -338,7 +338,7 @@ func (l *Lexer) readUnicodeMinusComment() Item {
 		sb.WriteRune(l.ch)
 		l.readChar()
 	}
-	return Item{Token: token.COMMENT, Value: sb.String(), Pos: pos}
+	return Item{Token: token.LINE_COMMENT, Value: sb.String(), Pos: pos}
 }
 
 func (l *Lexer) readBlockComment() Item {
@@ -371,7 +371,7 @@ func (l *Lexer) readBlockComment() Item {
 			l.readChar()
 		}
 	}
-	return Item{Token: token.COMMENT, Value: sb.String(), Pos: pos}
+	return Item{Token: token.LINE_COMMENT, Value: sb.String(), Pos: pos}
 }
 
 func (l *Lexer) readString(quote rune) Item {

parser/parser.go

@@ -37,7 +37,7 @@ func (p *Parser) nextToken() {
 	for {
 		p.peek = p.lexer.NextToken()
 		// Skip whitespace and comments
-		if p.peek.Token == token.WHITESPACE || p.peek.Token == token.COMMENT {
+		if p.peek.Token == token.WHITESPACE || p.peek.Token == token.LINE_COMMENT {
 			continue
 		}
 		break

token/token.go

@@ -9,7 +9,7 @@ const (
 	ILLEGAL Token = iota
 	EOF
 	WHITESPACE
-	COMMENT
+	LINE_COMMENT // SQL comments like -- and /* */
 
 	// Literals
 	IDENT   // identifiers
@@ -74,6 +74,7 @@ const (
 	COLLATE
 	COLUMN
 	COLUMNS
+	COMMENT
 	COMMIT
 	CONSTRAINT
 	CREATE
@@ -208,7 +209,7 @@ var tokens = [...]string{
 	ILLEGAL:    "ILLEGAL",
 	EOF:        "EOF",
 	WHITESPACE: "WHITESPACE",
-	COMMENT:    "COMMENT",
+	LINE_COMMENT: "LINE_COMMENT",
 
 	IDENT:  "IDENT",
 	NUMBER: "NUMBER",
@@ -268,6 +269,7 @@ var tokens = [...]string{
 	COLLATE:      "COLLATE",
 	COLUMN:       "COLUMN",
 	COLUMNS:      "COLUMNS",
+	COMMENT:      "COMMENT",
 	COMMIT:       "COMMIT",
 	CONSTRAINT:   "CONSTRAINT",
 	CREATE:       "CREATE",