Handle ATTACH PARTITION ... FROM as REPLACE_PARTITION in EXPLAIN

Parse the FROM clause in ALTER TABLE ATTACH PARTITION statements
and show it as REPLACE_PARTITION in EXPLAIN AST output to match
ClickHouse's behavior.

Fixes multiple tests across several test files.

Author: claude

internal/explain/statements.go

@@ -1620,6 +1620,10 @@ func explainAlterCommand(sb *strings.Builder, cmd *ast.AlterCommand, indent stri
 	if cmdType == ast.AlterClearStatistics {
 		cmdType = ast.AlterDropStatistics
 	}
+	// ATTACH PARTITION ... FROM table is shown as REPLACE_PARTITION in EXPLAIN AST
+	if cmdType == ast.AlterAttachPartition && cmd.FromTable != "" {
+		cmdType = ast.AlterReplacePartition
+	}
 	// DETACH_PARTITION is shown as DROP_PARTITION in EXPLAIN AST
 	if cmdType == ast.AlterDetachPartition {
 		cmdType = ast.AlterDropPartition

parser/parser.go

@@ -5817,6 +5817,14 @@ func (p *Parser) parseAlterCommand() *ast.AlterCommand {
 				cmd.PartitionIsID = true
 			}
 			cmd.Partition = p.parseExpression(LOWEST)
+			// Handle FROM table (ATTACH PARTITION ... FROM table)
+			if p.currentIs(token.FROM) {
+				p.nextToken()
+				if p.currentIs(token.IDENT) || p.current.Token.IsKeyword() {
+					cmd.FromTable = p.current.Value
+					p.nextToken()
+				}
+			}
 		} else if p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "PART" {
 			// ATTACH PART uses ATTACH_PARTITION type in ClickHouse EXPLAIN
 			cmd.Type = ast.AlterAttachPartition

parser/testdata/00626_replace_partition_from_table/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt44": true,
-    "stmt46": true
-  }
-}
+{}

parser/testdata/01055_compact_parts_1/metadata.json

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

parser/testdata/01710_minmax_count_projection/metadata.json

@@ -1,6 +1,5 @@
 {
   "explain_todo": {
-    "stmt20": true,
     "stmt33": true
   }
 }

parser/testdata/01901_test_attach_partition_from/metadata.json

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

parser/testdata/02731_replace_partition_from_temporary_table/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt31": true,
-    "stmt34": true
-  }
-}
+{}

parser/testdata/02998_projection_after_attach_partition/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt11": true
-  }
-}
+{}