Add FETCH PARTITION support and fix PARTITION ALL child count

- Add AlterFetchPartition and AlterMovePartition types to AST
- Add FromPath field to AlterCommand for FETCH PARTITION FROM
- Implement FETCH PARTITION parsing in parseAlterCommand
- Fix children count for PARTITION ALL (now counts as 1 child)
- Add explain support for FETCH_PARTITION and MOVE_PARTITION

Fixes stmt42 in 00753_alter_attach and other FETCH PARTITION tests.

Author: claude

ast/ast.go

@@ -529,6 +529,7 @@ type AlterCommand struct {
 	ConstraintName string               `json:"constraint_name,omitempty"`
 	Partition      Expression           `json:"partition,omitempty"`
 	FromTable      string               `json:"from_table,omitempty"`
+	FromPath       string               `json:"from_path,omitempty"` // For FETCH PARTITION FROM
 	TTL            *TTLClause           `json:"ttl,omitempty"`
 	Settings       []*SettingExpr       `json:"settings,omitempty"`
 	Where          Expression           `json:"where,omitempty"`       // For DELETE WHERE
@@ -593,6 +594,8 @@ const (
 	AlterDetachPartition    AlterCommandType = "DETACH_PARTITION"
 	AlterAttachPartition    AlterCommandType = "ATTACH_PARTITION"
 	AlterReplacePartition   AlterCommandType = "REPLACE_PARTITION"
+	AlterFetchPartition     AlterCommandType = "FETCH_PARTITION"
+	AlterMovePartition      AlterCommandType = "MOVE_PARTITION"
 	AlterFreezePartition    AlterCommandType = "FREEZE_PARTITION"
 	AlterFreeze             AlterCommandType = "FREEZE"
 	AlterDeleteWhere        AlterCommandType = "DELETE_WHERE"

internal/explain/statements.go

@@ -1091,7 +1091,7 @@ func explainAlterCommand(sb *strings.Builder, cmd *ast.AlterCommand, indent stri
 	case ast.AlterModifySetting:
 		fmt.Fprintf(sb, "%s Set\n", indent)
 	case ast.AlterDropPartition, ast.AlterDetachPartition, ast.AlterAttachPartition,
-		ast.AlterReplacePartition, ast.AlterFreezePartition:
+		ast.AlterReplacePartition, ast.AlterFetchPartition, ast.AlterMovePartition, ast.AlterFreezePartition:
 		if cmd.Partition != nil {
 			// PARTITION ALL is shown as Partition_ID (empty) in EXPLAIN AST
 			if ident, ok := cmd.Partition.(*ast.Identifier); ok && strings.ToUpper(ident.Name()) == "ALL" {
@@ -1284,12 +1284,9 @@ func countAlterCommandChildren(cmd *ast.AlterCommand) int {
 	case ast.AlterModifySetting:
 		children = 1
 	case ast.AlterDropPartition, ast.AlterDetachPartition, ast.AlterAttachPartition,
-		ast.AlterReplacePartition, ast.AlterFreezePartition:
+		ast.AlterReplacePartition, ast.AlterFetchPartition, ast.AlterMovePartition, ast.AlterFreezePartition:
 		if cmd.Partition != nil {
-			// PARTITION ALL doesn't count as a child (shown as Partition_ID empty)
-			if ident, ok := cmd.Partition.(*ast.Identifier); !ok || strings.ToUpper(ident.Name()) != "ALL" {
-				children++
-			}
+			children++
 		}
 	case ast.AlterFreeze:
 		// No children

parser/parser.go

@@ -4179,6 +4179,21 @@ func (p *Parser) parseAlterCommand() *ast.AlterCommand {
 				}
 			}
 		}
+	case token.FETCH:
+		p.nextToken()
+		if p.currentIs(token.PARTITION) {
+			cmd.Type = ast.AlterFetchPartition
+			p.nextToken()
+			cmd.Partition = p.parseExpression(LOWEST)
+			// FROM path
+			if p.currentIs(token.FROM) {
+				p.nextToken()
+				if p.currentIs(token.STRING) {
+					cmd.FromPath = p.current.Value
+					p.nextToken()
+				}
+			}
+		}
 	case token.DELETE:
 		// DELETE WHERE condition - mutation to delete rows
 		cmd.Type = ast.AlterDeleteWhere

parser/testdata/00753_alter_attach/metadata.json

@@ -1,25 +1,9 @@
 {
   "explain_todo": {
-    "stmt14": true,
-    "stmt22": true,
-    "stmt34": true,
-    "stmt42": true,
-    "stmt51": true,
     "stmt52": true,
     "stmt53": true,
     "stmt54": true,
     "stmt55": true,
-    "stmt56": true,
-    "stmt58": true,
-    "stmt63": true,
-    "stmt65": true,
-    "stmt69": true,
-    "stmt71": true,
-    "stmt73": true,
-    "stmt77": true,
-    "stmt79": true,
-    "stmt83": true,
-    "stmt85": true,
-    "stmt87": true
+    "stmt58": true
   }
 }

parser/testdata/01015_attach_part/metadata.json

@@ -1,7 +1,6 @@
 {
   "explain_todo": {
     "stmt5": true,
-    "stmt7": true,
-    "stmt9": true
+    "stmt7": true
   }
 }

parser/testdata/01166_truncate_multiple_partitions/metadata.json

@@ -3,13 +3,11 @@
     "stmt10": true,
     "stmt11": true,
     "stmt17": true,
-    "stmt20": true,
     "stmt22": true,
     "stmt23": true,
     "stmt24": true,
     "stmt25": true,
     "stmt3": true,
-    "stmt6": true,
     "stmt8": true,
     "stmt9": true
   }

parser/testdata/01650_fetch_patition_with_macro_in_zk_path_long/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt6": true
-  }
-}
+{}

parser/testdata/03203_drop_detached_partition_all/metadata.json

@@ -1,6 +1,5 @@
 {
   "explain_todo": {
-    "stmt5": true,
     "stmt7": true
   }
 }

parser/testdata/03350_alter_table_fetch_partition_thread_pool/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt8": true
-  }
-}
+{}