Support TTL DELETE WHERE clause in ALTER TABLE MODIFY TTL

- Update ALTER MODIFY TTL parsing to use parseTTLElement
- Capture WHERE condition in TTLElement for conditional deletion
- Update explain code to output TTLElement with WHERE as child

Author: claude

internal/explain/statements.go

@@ -1773,9 +1773,23 @@ func explainAlterCommand(sb *strings.Builder, cmd *ast.AlterCommand, indent stri
 			fmt.Fprintf(sb, "%s Identifier %s\n", indent, cmd.ConstraintName)
 		}
 	case ast.AlterModifyTTL:
-		if cmd.TTL != nil && cmd.TTL.Expression != nil {
+		if cmd.TTL != nil && len(cmd.TTL.Elements) > 0 {
 			// TTL is wrapped in ExpressionList and TTLElement
-			// Count total TTL elements (1 for Expression + len(Expressions))
+			fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, len(cmd.TTL.Elements))
+			for _, elem := range cmd.TTL.Elements {
+				// Count children: 1 for Expr, +1 for Where if present
+				ttlChildren := 1
+				if elem.Where != nil {
+					ttlChildren++
+				}
+				fmt.Fprintf(sb, "%s  TTLElement (children %d)\n", indent, ttlChildren)
+				Node(sb, elem.Expr, depth+3)
+				if elem.Where != nil {
+					Node(sb, elem.Where, depth+3)
+				}
+			}
+		} else if cmd.TTL != nil && cmd.TTL.Expression != nil {
+			// Fallback for backward compatibility (Expression/Expressions fields)
 			ttlCount := 1 + len(cmd.TTL.Expressions)
 			fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, ttlCount)
 			fmt.Fprintf(sb, "%s  TTLElement (children 1)\n", indent)

parser/parser.go

@@ -5682,18 +5682,24 @@ func (p *Parser) parseAlterCommand() *ast.AlterCommand {
 			cmd.Type = ast.AlterModifyTTL
 			p.nextToken()
 			cmd.TTL = &ast.TTLClause{
-				Position:   p.current.Pos,
-				Expression: p.parseExpression(LOWEST),
+				Position: p.current.Pos,
 			}
-			// Skip RECOMPRESS CODEC(...) and other TTL modifiers
-			p.skipTTLModifiers()
-			// Parse additional TTL elements (comma-separated)
-			for p.currentIs(token.COMMA) {
-				p.nextToken() // skip comma
-				expr := p.parseExpression(LOWEST)
-				cmd.TTL.Expressions = append(cmd.TTL.Expressions, expr)
-				// Skip RECOMPRESS CODEC(...) if present
-				p.skipTTLModifiers()
+			// Parse TTL elements using parseTTLElement (captures WHERE clause)
+			for {
+				elem := p.parseTTLElement()
+				cmd.TTL.Elements = append(cmd.TTL.Elements, elem)
+				if p.currentIs(token.COMMA) {
+					p.nextToken()
+				} else {
+					break
+				}
+			}
+			// Keep backward compatibility with Expression/Expressions fields
+			if len(cmd.TTL.Elements) > 0 {
+				cmd.TTL.Expression = cmd.TTL.Elements[0].Expr
+				for i := 1; i < len(cmd.TTL.Elements); i++ {
+					cmd.TTL.Expressions = append(cmd.TTL.Expressions, cmd.TTL.Elements[i].Expr)
+				}
 			}
 		} else if p.currentIs(token.SETTINGS) || (p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "SETTING") {
 			// Both SETTINGS and SETTING (singular) are accepted

parser/testdata/02129_add_column_add_ttl/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt17": true,
-    "stmt7": true
-  }
-}
+{}