Add PARTITION BY support and fix tuple expansion

- Add PARTITION BY output to CREATE TABLE Storage definition
- Treat nested tuple/array literals as complex expressions for expansion

This fixes 20 more tests (5849 -> 5869 passing).

Author: claude

internal/explain/expressions.go

@@ -29,7 +29,9 @@ func explainLiteral(sb *strings.Builder, n *ast.Literal, indent string, depth in
 			}
 			hasComplexExpr := false
 			for _, e := range exprs {
-				if _, isLit := e.(*ast.Literal); !isLit {
+				lit, isLit := e.(*ast.Literal)
+				// Non-literals or tuple/array literals count as complex
+				if !isLit || (isLit && (lit.Type == ast.LiteralTuple || lit.Type == ast.LiteralArray)) {
 					hasComplexExpr = true
 					break
 				}

internal/explain/statements.go

@@ -56,7 +56,7 @@ func explainCreateQuery(sb *strings.Builder, n *ast.CreateQuery, indent string,
 	if len(n.Columns) > 0 {
 		children++
 	}
-	if n.Engine != nil || len(n.OrderBy) > 0 || len(n.PrimaryKey) > 0 {
+	if n.Engine != nil || len(n.OrderBy) > 0 || len(n.PrimaryKey) > 0 || n.PartitionBy != nil {
 		children++
 	}
 	if n.AsSelect != nil {
@@ -76,11 +76,14 @@ func explainCreateQuery(sb *strings.Builder, n *ast.CreateQuery, indent string,
 			Column(sb, col, depth+3)
 		}
 	}
-	if n.Engine != nil || len(n.OrderBy) > 0 || len(n.PrimaryKey) > 0 || len(n.Settings) > 0 {
+	if n.Engine != nil || len(n.OrderBy) > 0 || len(n.PrimaryKey) > 0 || n.PartitionBy != nil || len(n.Settings) > 0 {
 		storageChildren := 0
 		if n.Engine != nil {
 			storageChildren++
 		}
+		if n.PartitionBy != nil {
+			storageChildren++
+		}
 		if len(n.OrderBy) > 0 {
 			storageChildren++
 		}
@@ -106,6 +109,13 @@ func explainCreateQuery(sb *strings.Builder, n *ast.CreateQuery, indent string,
 				fmt.Fprintf(sb, "%s  Function %s\n", indent, n.Engine.Name)
 			}
 		}
+		if n.PartitionBy != nil {
+			if ident, ok := n.PartitionBy.(*ast.Identifier); ok {
+				fmt.Fprintf(sb, "%s  Identifier %s\n", indent, ident.Name())
+			} else {
+				Node(sb, n.PartitionBy, depth+2)
+			}
+		}
 		if len(n.OrderBy) > 0 {
 			if len(n.OrderBy) == 1 {
 				if ident, ok := n.OrderBy[0].(*ast.Identifier); ok {