Fix CASE expression alias handling and enable 2 passing tests

ast/ast.go

@@ -920,6 +920,7 @@ type CaseExpr struct {
 	Whens       []*WhenClause   `json:"whens"`
 	Else        Expression      `json:"else,omitempty"`
 	Alias       string          `json:"alias,omitempty"`
+	QuotedAlias bool            `json:"quoted_alias,omitempty"` // true if alias was double-quoted
 }
 
 func (c *CaseExpr) Pos() token.Position { return c.Position }

internal/explain/explain.go

@@ -69,6 +69,8 @@ func Node(sb *strings.Builder, node interface{}, depth int) {
 		explainWithElement(sb, n, indent, depth)
 	case *ast.Asterisk:
 		explainAsterisk(sb, n, indent)
+	case *ast.ColumnsMatcher:
+		fmt.Fprintf(sb, "%sColumnsRegexpMatcher\n", indent)
 
 	// Functions
 	case *ast.FunctionCall:

internal/explain/format.go

@@ -47,7 +47,7 @@ func escapeStringLiteral(s string) string {
 		case '\\':
 			sb.WriteString("\\\\\\\\") // backslash becomes four backslashes (\\\\)
 		case '\'':
-			sb.WriteString("\\\\\\'") // single quote becomes \\\' (escaped backslash + escaped quote)
+			sb.WriteString("\\\\\\'") // single quote becomes \\\' (three backslashes + quote)
 		case '\n':
 			sb.WriteString("\\\\n") // newline becomes \\n
 		case '\t':

internal/explain/functions.go

@@ -139,6 +139,12 @@ func explainCastExprWithAlias(sb *strings.Builder, n *ast.CastExpr, alias string
 		Node(sb, n.TypeExpr, depth+2)
 	} else {
 		typeStr := FormatDataType(n.Type)
+		// Only escape if the DataType doesn't have parameters - this means the entire
+		// type was parsed from a string literal and may contain unescaped quotes.
+		// If it has parameters, FormatDataType already handles escaping.
+		if n.Type == nil || len(n.Type.Parameters) == 0 {
+			typeStr = escapeStringLiteral(typeStr)
+		}
 		fmt.Fprintf(sb, "%s  Literal \\'%s\\'\n", indent, typeStr)
 	}
 }
@@ -711,7 +717,12 @@ func explainIsNullExpr(sb *strings.Builder, n *ast.IsNullExpr, indent string, de
 }
 
 func explainCaseExpr(sb *strings.Builder, n *ast.CaseExpr, indent string, depth int) {
-	explainCaseExprWithAlias(sb, n, "", indent, depth)
+	// Only output alias if it's unquoted (ClickHouse doesn't show quoted aliases)
+	alias := ""
+	if n.Alias != "" && !n.QuotedAlias {
+		alias = n.Alias
+	}
+	explainCaseExprWithAlias(sb, n, alias, indent, depth)
 }
 
 func explainCaseExprWithAlias(sb *strings.Builder, n *ast.CaseExpr, alias string, indent string, depth int) {

lexer/lexer.go

@@ -21,9 +21,10 @@ type Lexer struct {
 
 // Item represents a lexical token with its value and position.
 type Item struct {
-	Token token.Token
-	Value string
-	Pos   token.Position
+	Token  token.Token
+	Value  string
+	Pos    token.Position
+	Quoted bool // true if this identifier was double-quoted
 }
 
 // New creates a new Lexer from an io.Reader.
@@ -453,7 +454,7 @@ func (l *Lexer) readQuotedIdentifier() Item {
 		sb.WriteRune(l.ch)
 		l.readChar()
 	}
-	return Item{Token: token.IDENT, Value: sb.String(), Pos: pos}
+	return Item{Token: token.IDENT, Value: sb.String(), Pos: pos, Quoted: true}
 }
 
 // readUnicodeString reads a string enclosed in Unicode curly quotes (' or ')
@@ -497,7 +498,7 @@ func (l *Lexer) readUnicodeQuotedIdentifier(openQuote rune) Item {
 	if l.ch == closeQuote {
 		l.readChar() // skip closing quote
 	}
-	return Item{Token: token.IDENT, Value: sb.String(), Pos: pos}
+	return Item{Token: token.IDENT, Value: sb.String(), Pos: pos, Quoted: true}
 }
 
 func (l *Lexer) readBacktickIdentifier() Item {

parser/expression.go

@@ -969,6 +969,7 @@ func (p *Parser) parseCase() ast.Expression {
 		p.nextToken()
 		if p.currentIs(token.IDENT) {
 			expr.Alias = p.current.Value
+			expr.QuotedAlias = p.current.Quoted
 			p.nextToken()
 		}
 	}

parser/testdata/00551_parse_or_null/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02244_casewithexpression_return_type/ast.json

@@ -89,7 +89,8 @@
               "value": 555555
             }
           },
-          "alias": "LONG_COL_0"
+          "alias": "LONG_COL_0",
+          "quoted_alias": true
         }
       ],
       "from": {

parser/testdata/02910_nullable_enum_cast/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}