Fix EXPLAIN prefix format and enable 11 more tests (#22)

EXPLAIN output fix:
- At top level, ClickHouse outputs "Explain EXPLAIN <TYPE>"
- Nested in subqueries, it outputs "Explain <TYPE>"
- Added depth check to handle both cases correctly
- Also fixed EXPLAIN CURRENT TRANSACTION case

Tests enabled:
- 01029_early_constant_folding
- 01840_tupleElement_formatting_fuzzer
- 02210_processors_profile_log
- 02220_array_join_format
- 02315_replace_multiif_to_if
- 02377_executable_function_settings
- 02477_is_null_parser
- 02752_is_null_priority
- 02889_system_drop_format_schema
- 02893_system_drop_schema_cache_format
- 03155_explain_current_transaction

Author: claude

internal/explain/statements.go

@@ -297,10 +297,21 @@ func explainSystemQuery(sb *strings.Builder, indent string) {
 func explainExplainQuery(sb *strings.Builder, n *ast.ExplainQuery, indent string, depth int) {
 	// EXPLAIN CURRENT TRANSACTION has no children
 	if n.ExplainType == ast.ExplainCurrentTransaction {
-		fmt.Fprintf(sb, "%sExplain %s\n", indent, n.ExplainType)
+		// At top level (depth 0), ClickHouse outputs "Explain EXPLAIN <TYPE>"
+		if depth == 0 {
+			fmt.Fprintf(sb, "%sExplain EXPLAIN %s\n", indent, n.ExplainType)
+		} else {
+			fmt.Fprintf(sb, "%sExplain %s\n", indent, n.ExplainType)
+		}
 		return
 	}
-	fmt.Fprintf(sb, "%sExplain %s (children %d)\n", indent, n.ExplainType, 1)
+	// At top level (depth 0), ClickHouse outputs "Explain EXPLAIN <TYPE>"
+	// Nested in subqueries, it outputs "Explain <TYPE>"
+	if depth == 0 {
+		fmt.Fprintf(sb, "%sExplain EXPLAIN %s (children %d)\n", indent, n.ExplainType, 1)
+	} else {
+		fmt.Fprintf(sb, "%sExplain %s (children %d)\n", indent, n.ExplainType, 1)
+	}
 	Node(sb, n.Statement, depth+1)
 }
 

parser/testdata/01029_early_constant_folding/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/01840_tupleElement_formatting_fuzzer/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02210_processors_profile_log/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02220_array_join_format/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02315_replace_multiif_to_if/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02377_executable_function_settings/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02477_is_null_parser/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02752_is_null_priority/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/02889_system_drop_format_schema/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}