Fix SYSTEM query EXPLAIN output and parsing

- Add table/database as children in SYSTEM query explain output
- Exclude FLUSH LOGS command from showing table name as child
- Add INDEX, INSERT, PRIMARY, KEY tokens to isSystemCommandKeyword
- Add QUEUE to system command identifiers list

Author: claude

internal/explain/statements.go

@@ -516,7 +516,31 @@ func explainSetQuery(sb *strings.Builder, indent string) {
 }
 
 func explainSystemQuery(sb *strings.Builder, n *ast.SystemQuery, indent string) {
-	fmt.Fprintf(sb, "%sSYSTEM query\n", indent)
+	// Some commands like FLUSH LOGS don't show the log name as a child
+	// For other commands, table/database names are shown as children
+	isFlushLogs := strings.HasPrefix(strings.ToUpper(n.Command), "FLUSH LOGS")
+
+	// Count children - database and table are children if present and not FLUSH LOGS
+	children := 0
+	if !isFlushLogs {
+		if n.Database != "" {
+			children++
+		}
+		if n.Table != "" {
+			children++
+		}
+	}
+	if children > 0 {
+		fmt.Fprintf(sb, "%sSYSTEM query (children %d)\n", indent, children)
+		if n.Database != "" {
+			fmt.Fprintf(sb, "%s Identifier %s\n", indent, n.Database)
+		}
+		if n.Table != "" {
+			fmt.Fprintf(sb, "%s Identifier %s\n", indent, n.Table)
+		}
+	} else {
+		fmt.Fprintf(sb, "%sSYSTEM query\n", indent)
+	}
 }
 
 func explainExplainQuery(sb *strings.Builder, n *ast.ExplainQuery, indent string, depth int) {

parser/parser.go

@@ -4359,13 +4359,15 @@ func (p *Parser) parseSystem() *ast.SystemQuery {
 // isSystemCommandKeyword returns true if current token is a keyword that can be part of SYSTEM command
 func (p *Parser) isSystemCommandKeyword() bool {
 	switch p.current.Token {
-	case token.TTL, token.SYNC, token.DROP, token.FORMAT, token.FOR:
+	case token.TTL, token.SYNC, token.DROP, token.FORMAT, token.FOR, token.INDEX, token.INSERT,
+		token.PRIMARY, token.KEY:
 		return true
 	}
-	// Handle SCHEMA, CACHE as identifiers since they're not keyword tokens
+	// Handle SCHEMA, CACHE, QUEUE and other identifiers that are part of SYSTEM commands
 	if p.currentIs(token.IDENT) {
 		upper := strings.ToUpper(p.current.Value)
-		if upper == "SCHEMA" || upper == "CACHE" {
+		switch upper {
+		case "SCHEMA", "CACHE", "QUEUE":
 			return true
 		}
 	}

parser/testdata/02354_read_in_order_prewhere/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt3": true
-  }
-}
+{}