Fix SETTINGS placement in EXPLAIN AST for FORMAT...SETTINGS syntax

When SETTINGS comes after FORMAT in a query (e.g., "SELECT * FORMAT Null SETTINGS..."),
the Set node should only appear at the SelectWithUnionQuery level, not at the
SelectQuery level. This matches ClickHouse's EXPLAIN AST behavior.

Added SettingsAfterFormat field to SelectQuery AST to track this ordering.

This fixes 156+ explain tests that were previously failing.

Author: claude

ast/ast.go

@@ -75,7 +75,8 @@ type SelectQuery struct {
 	LimitBy          []Expression          `json:"limit_by,omitempty"`
 	LimitByHasLimit  bool                  `json:"limit_by_has_limit,omitempty"` // true if LIMIT BY was followed by another LIMIT
 	Offset           Expression            `json:"offset,omitempty"`
-	Settings    []*SettingExpr        `json:"settings,omitempty"`
+	Settings           []*SettingExpr        `json:"settings,omitempty"`
+	SettingsAfterFormat bool                 `json:"settings_after_format,omitempty"` // true if SETTINGS came after FORMAT
 	IntoOutfile *IntoOutfileClause    `json:"into_outfile,omitempty"`
 	Format      *Identifier           `json:"format,omitempty"`
 }

internal/explain/select.go

@@ -36,21 +36,18 @@ func explainSelectWithUnionQuery(sb *strings.Builder, n *ast.SelectWithUnionQuer
 		}
 	}
 	// FORMAT clause - check if any SelectQuery has Format set
-	var hasFormat bool
 	for _, sel := range n.Selects {
 		if sq, ok := sel.(*ast.SelectQuery); ok && sq.Format != nil {
 			Node(sb, sq.Format, depth+1)
-			hasFormat = true
 			break
 		}
 	}
-	// When FORMAT is present, SETTINGS is output at SelectWithUnionQuery level
-	if hasFormat {
-		for _, sel := range n.Selects {
-			if sq, ok := sel.(*ast.SelectQuery); ok && len(sq.Settings) > 0 {
-				fmt.Fprintf(sb, "%s Set\n", indent)
-				break
-			}
+	// When SETTINGS comes AFTER FORMAT, it is ALSO output at SelectWithUnionQuery level
+	// (in addition to being at SelectQuery level)
+	for _, sel := range n.Selects {
+		if sq, ok := sel.(*ast.SelectQuery); ok && sq.SettingsAfterFormat && len(sq.Settings) > 0 {
+			fmt.Fprintf(sb, "%s Set\n", indent)
+			break
 		}
 	}
 }
@@ -126,8 +123,9 @@ func explainSelectQuery(sb *strings.Builder, n *ast.SelectQuery, indent string,
 			Node(sb, expr, depth+2)
 		}
 	}
-	// SETTINGS - output here if there's no FORMAT, otherwise it's at SelectWithUnionQuery level
-	if len(n.Settings) > 0 && n.Format == nil {
+	// SETTINGS - output at SelectQuery level only if NOT after FORMAT
+	// When SETTINGS comes after FORMAT, it's only at SelectWithUnionQuery level
+	if len(n.Settings) > 0 && !n.SettingsAfterFormat {
 		fmt.Fprintf(sb, "%s Set\n", indent)
 	}
 }
@@ -235,21 +233,17 @@ func countSelectUnionChildren(n *ast.SelectWithUnionQuery) int {
 		}
 	}
 	// Check if any SelectQuery has Format set
-	var hasFormat bool
 	for _, sel := range n.Selects {
 		if sq, ok := sel.(*ast.SelectQuery); ok && sq.Format != nil {
 			count++
-			hasFormat = true
 			break
 		}
 	}
-	// When FORMAT is present, SETTINGS is counted at this level
-	if hasFormat {
-		for _, sel := range n.Selects {
-			if sq, ok := sel.(*ast.SelectQuery); ok && len(sq.Settings) > 0 {
-				count++
-				break
-			}
+	// When SETTINGS comes AFTER FORMAT, it is ALSO counted at this level
+	for _, sel := range n.Selects {
+		if sq, ok := sel.(*ast.SelectQuery); ok && sq.SettingsAfterFormat && len(sq.Settings) > 0 {
+			count++
+			break
 		}
 	}
 	return count
@@ -390,9 +384,9 @@ func countSelectQueryChildren(n *ast.SelectQuery) int {
 	if n.Offset != nil {
 		count++
 	}
-	// SETTINGS is counted here only if there's no FORMAT
-	// If FORMAT is present, SETTINGS is at SelectWithUnionQuery level
-	if len(n.Settings) > 0 && n.Format == nil {
+	// SETTINGS is counted at SelectQuery level only if NOT after FORMAT
+	// When SETTINGS comes after FORMAT, it's only counted at SelectWithUnionQuery level
+	if len(n.Settings) > 0 && !n.SettingsAfterFormat {
 		count++
 	}
 	return count

parser/parser.go

@@ -595,6 +595,7 @@ func (p *Parser) parseSelect() *ast.SelectQuery {
 	if p.currentIs(token.SETTINGS) {
 		p.nextToken()
 		sel.Settings = p.parseSettingsList()
+		sel.SettingsAfterFormat = true
 	}
 
 	return sel