Fix NULL casing and Enum type parameter handling

- Change NULL literal output from 'Null' to 'NULL' (uppercase)
- Fix DataType with complex parameters (like Enum) to output as
  children with ExpressionList instead of formatted string
- Update Column function to use Node() for type output

Tests passing: 5179 (up from 5128)

Author: claude

internal/explain/explain.go

@@ -116,7 +116,7 @@ func Node(sb *strings.Builder, node interface{}, depth int) {
 
 	// Types
 	case *ast.DataType:
-		explainDataType(sb, n, indent)
+		explainDataType(sb, n, indent, depth)
 	case *ast.Parameter:
 		explainParameter(sb, n, indent)
 
@@ -165,7 +165,7 @@ func Column(sb *strings.Builder, col *ast.ColumnDeclaration, depth int) {
 	}
 	fmt.Fprintf(sb, "%sColumnDeclaration %s (children %d)\n", indent, col.Name, children)
 	if col.Type != nil {
-		fmt.Fprintf(sb, "%s DataType %s\n", indent, FormatDataType(col.Type))
+		Node(sb, col.Type, depth+1)
 	}
 	if col.Default != nil {
 		Node(sb, col.Default, depth+1)

internal/explain/format.go

@@ -30,7 +30,7 @@ func FormatLiteral(lit *ast.Literal) string {
 		}
 		return "UInt8_0"
 	case ast.LiteralNull:
-		return "Null"
+		return "NULL"
 	case ast.LiteralArray:
 		return formatArrayLiteral(lit.Value)
 	case ast.LiteralTuple:

internal/explain/statements.go

@@ -138,8 +138,30 @@ func explainDescribeQuery(sb *strings.Builder, n *ast.DescribeQuery, indent stri
 	fmt.Fprintf(sb, "%sDescribe %s\n", indent, name)
 }
 
-func explainDataType(sb *strings.Builder, n *ast.DataType, indent string) {
-	fmt.Fprintf(sb, "%sDataType %s\n", indent, FormatDataType(n))
+func explainDataType(sb *strings.Builder, n *ast.DataType, indent string, depth int) {
+	// Check if type has complex parameters (expressions, not just literals/types)
+	hasComplexParams := false
+	for _, p := range n.Parameters {
+		if _, ok := p.(*ast.Literal); ok {
+			continue
+		}
+		if _, ok := p.(*ast.DataType); ok {
+			continue
+		}
+		hasComplexParams = true
+		break
+	}
+
+	if hasComplexParams && len(n.Parameters) > 0 {
+		// Complex parameters need to be output as children
+		fmt.Fprintf(sb, "%sDataType %s (children %d)\n", indent, n.Name, 1)
+		fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, len(n.Parameters))
+		for _, p := range n.Parameters {
+			Node(sb, p, depth+2)
+		}
+	} else {
+		fmt.Fprintf(sb, "%sDataType %s\n", indent, FormatDataType(n))
+	}
 }
 
 func explainParameter(sb *strings.Builder, n *ast.Parameter, indent string) {