Add EXPLAIN options capture and viewExplain wrapper transformation

- Add OptionsString field to ExplainQuery to capture EXPLAIN options
- Update parser to capture options like "actions = 1" as strings
- Update explainViewExplain to output proper SELECT * FROM viewExplain() structure
- This matches ClickHouse's internal transformation of EXPLAIN as table source

Updates metadata for many passing explain tests.

Author: claude

ast/ast.go

@@ -700,11 +700,12 @@ const (
 
 // ExplainQuery represents an EXPLAIN statement.
 type ExplainQuery struct {
-	Position     token.Position `json:"-"`
-	ExplainType  ExplainType    `json:"explain_type"`
-	Statement    Statement      `json:"statement"`
-	HasSettings  bool           `json:"has_settings,omitempty"`
-	ExplicitType bool           `json:"explicit_type,omitempty"` // true if type was explicitly specified
+	Position       token.Position `json:"-"`
+	ExplainType    ExplainType    `json:"explain_type"`
+	Statement      Statement      `json:"statement"`
+	HasSettings    bool           `json:"has_settings,omitempty"`
+	ExplicitType   bool           `json:"explicit_type,omitempty"` // true if type was explicitly specified
+	OptionsString  string         `json:"options_string,omitempty"` // Formatted options like "actions = 1"
 }
 
 func (e *ExplainQuery) Pos() token.Position { return e.Position }

internal/explain/tables.go

@@ -133,22 +133,30 @@ func abs(x float64) float64 {
 }
 
 // explainViewExplain handles EXPLAIN queries used as table sources, converting to viewExplain function
+// ClickHouse internally transforms EXPLAIN to SELECT * FROM viewExplain(...)
 func explainViewExplain(sb *strings.Builder, n *ast.ExplainQuery, alias string, indent string, depth int) {
-	// When EXPLAIN is used as a table source, it becomes viewExplain function
-	// Arguments: 'EXPLAIN', 'options', subquery
-	fmt.Fprintf(sb, "%sFunction viewExplain (children %d)\n", indent, 1)
-	fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, 3)
+	// When EXPLAIN is used as a table source, it becomes wrapped in SELECT * FROM viewExplain(...)
+	// Structure: Subquery -> SelectWithUnionQuery -> ExpressionList -> SelectQuery -> Asterisk, TablesInSelectQuery -> viewExplain
+	fmt.Fprintf(sb, "%sSubquery (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s SelectWithUnionQuery (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s  ExpressionList (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s   SelectQuery (children %d)\n", indent, 2)
+	fmt.Fprintf(sb, "%s    ExpressionList (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s     Asterisk\n", indent)
+	fmt.Fprintf(sb, "%s    TablesInSelectQuery (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s     TablesInSelectQueryElement (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s      TableExpression (children %d)\n", indent, 1)
+	// Now output the viewExplain function
+	fmt.Fprintf(sb, "%s       Function viewExplain (children %d)\n", indent, 1)
+	fmt.Fprintf(sb, "%s        ExpressionList (children %d)\n", indent, 3)
 	// First argument: 'EXPLAIN' literal
-	fmt.Fprintf(sb, "%s  Literal \\'EXPLAIN\\'\n", indent)
-	// Second argument: options string (empty for now since we don't track detailed options)
-	options := string(n.ExplainType)
-	if options == "PLAN" {
-		options = ""
-	}
-	fmt.Fprintf(sb, "%s  Literal \\'%s\\'\n", indent, options)
+	fmt.Fprintf(sb, "%s         Literal \\'EXPLAIN\\'\n", indent)
+	// Second argument: options string (e.g., "actions = 1")
+	options := n.OptionsString
+	fmt.Fprintf(sb, "%s         Literal \\'%s\\'\n", indent, options)
 	// Third argument: the subquery being explained
-	fmt.Fprintf(sb, "%s  Subquery (children %d)\n", indent, 1)
-	Node(sb, n.Statement, depth+3)
+	fmt.Fprintf(sb, "%s         Subquery (children %d)\n", indent, 1)
+	Node(sb, n.Statement, depth+10)
 }
 
 func explainTableIdentifierWithAlias(sb *strings.Builder, n *ast.TableIdentifier, alias string, indent string) {

parser/parser.go

@@ -4312,17 +4312,27 @@ func (p *Parser) parseExplain() *ast.ExplainQuery {
 	// Parse EXPLAIN options (e.g., header = 1, optimize = 0)
 	// These come before the actual statement
 	// Options can be identifiers or keywords like OPTIMIZE followed by =
+	var optionParts []string
 	for p.peekIs(token.EQ) && !p.currentIs(token.SELECT) && !p.currentIs(token.WITH) {
 		// This is an option (name = value)
 		explain.HasSettings = true
+		optionName := p.current.Value
 		p.nextToken() // skip option name
 		p.nextToken() // skip =
-		p.parseExpression(LOWEST) // skip value
+		// Get the value
+		optionValue := p.current.Value
+		if p.currentIs(token.NUMBER) || p.currentIs(token.STRING) || p.currentIs(token.IDENT) {
+			optionParts = append(optionParts, optionName+" = "+optionValue)
+		}
+		p.parseExpression(LOWEST) // skip value expression (may consume more tokens)
 		// Skip comma if present
 		if p.currentIs(token.COMMA) {
 			p.nextToken()
 		}
 	}
+	if len(optionParts) > 0 {
+		explain.OptionsString = strings.Join(optionParts, ", ")
+	}
 
 	// Parse the statement being explained
 	explain.Statement = p.parseStatement()

parser/testdata/00183_prewhere_conditions_order/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt5": true,
-    "stmt6": true
-  }
-}
+{}

parser/testdata/00944_minmax_nan/metadata.json

@@ -1,8 +1 @@
-{
-  "explain_todo": {
-    "stmt13": true,
-    "stmt14": true,
-    "stmt16": true,
-    "stmt17": true
-  }
-}
+{}

parser/testdata/01582_move_to_prewhere_compact_parts/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt11": true,
-    "stmt6": true
-  }
-}
+{}

parser/testdata/01625_constraints_index_append/metadata.json

@@ -1,13 +1,5 @@
 {
   "explain_todo": {
-    "stmt12": true,
-    "stmt13": true,
-    "stmt14": true,
-    "stmt15": true,
-    "stmt16": true,
-    "stmt17": true,
-    "stmt18": true,
-    "stmt19": true,
     "stmt5": true
   }
 }

parser/testdata/01655_plan_optimizations_merge_filters/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt3": true,
-    "stmt5": true
-  }
-}
+{}

parser/testdata/01710_projection_pk_trivial_count/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt5": true
-  }
-}
+{}

parser/testdata/01737_move_order_key_to_prewhere_select_final/metadata.json

@@ -1,18 +1 @@
-{
-  "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
-    "stmt12": true,
-    "stmt13": true,
-    "stmt14": true,
-    "stmt15": true,
-    "stmt16": true,
-    "stmt17": true,
-    "stmt20": true,
-    "stmt21": true,
-    "stmt22": true,
-    "stmt23": true,
-    "stmt8": true,
-    "stmt9": true
-  }
-}
+{}