Add ALTER TABLE SPLIT/MERGE RANGE partition support

- Add AlterTableAlterPartitionStatement AST type for partition operations
- Add parsing support for ALTER TABLE table SPLIT/MERGE RANGE (value)
- Add JSON marshaling for the new statement type

Note: AlterTableStatementTests130 has additional differences related to
system versioning features (PERIOD FOR SYSTEM_TIME, SystemTimePeriodDefinition)
that need separate implementation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

ast/alter_table_alter_partition_statement.go

@@ -0,0 +1,11 @@
+package ast
+
+// AlterTableAlterPartitionStatement represents ALTER TABLE table SPLIT/MERGE RANGE (value)
+type AlterTableAlterPartitionStatement struct {
+	SchemaObjectName *SchemaObjectName
+	BoundaryValue    ScalarExpression
+	IsSplit          bool
+}
+
+func (*AlterTableAlterPartitionStatement) node()      {}
+func (*AlterTableAlterPartitionStatement) statement() {}

parser/marshal.go

@@ -591,6 +591,8 @@ func statementToJSON(stmt ast.Statement) jsonNode {
 		return alterTableSetStatementToJSON(s)
 	case *ast.AlterTableRebuildStatement:
 		return alterTableRebuildStatementToJSON(s)
+	case *ast.AlterTableAlterPartitionStatement:
+		return alterTableAlterPartitionStatementToJSON(s)
 	case *ast.AlterTableChangeTrackingModificationStatement:
 		return alterTableChangeTrackingStatementToJSON(s)
 	case *ast.InsertBulkStatement:
@@ -16934,6 +16936,20 @@ func alterTableRebuildStatementToJSON(s *ast.AlterTableRebuildStatement) jsonNod
 	return node
 }
 
+func alterTableAlterPartitionStatementToJSON(s *ast.AlterTableAlterPartitionStatement) jsonNode {
+	node := jsonNode{
+		"$type":   "AlterTableAlterPartitionStatement",
+		"IsSplit": s.IsSplit,
+	}
+	if s.BoundaryValue != nil {
+		node["BoundaryValue"] = scalarExpressionToJSON(s.BoundaryValue)
+	}
+	if s.SchemaObjectName != nil {
+		node["SchemaObjectName"] = schemaObjectNameToJSON(s.SchemaObjectName)
+	}
+	return node
+}
+
 func alterTableChangeTrackingStatementToJSON(s *ast.AlterTableChangeTrackingModificationStatement) jsonNode {
 	node := jsonNode{
 		"$type":               "AlterTableChangeTrackingModificationStatement",

parser/parse_ddl.go

@@ -5049,9 +5049,50 @@ func (p *Parser) parseAlterTableStatement() (ast.Statement, error) {
 		return p.parseAlterTableRebuildStatement(tableName)
 	}
 
+	// Check for SPLIT RANGE / MERGE RANGE (partition operations)
+	upperLit := strings.ToUpper(p.curTok.Literal)
+	if upperLit == "SPLIT" || upperLit == "MERGE" {
+		return p.parseAlterTableAlterPartitionStatement(tableName, upperLit == "SPLIT")
+	}
+
 	return nil, fmt.Errorf("unexpected token in ALTER TABLE: %s", p.curTok.Literal)
 }
 
+func (p *Parser) parseAlterTableAlterPartitionStatement(tableName *ast.SchemaObjectName, isSplit bool) (*ast.AlterTableAlterPartitionStatement, error) {
+	// Consume SPLIT or MERGE
+	p.nextToken()
+
+	// Expect RANGE
+	if strings.ToUpper(p.curTok.Literal) != "RANGE" {
+		return nil, fmt.Errorf("expected RANGE after SPLIT/MERGE, got %s", p.curTok.Literal)
+	}
+	p.nextToken()
+
+	// Expect (
+	if p.curTok.Type != TokenLParen {
+		return nil, fmt.Errorf("expected ( after RANGE, got %s", p.curTok.Literal)
+	}
+	p.nextToken()
+
+	// Parse boundary value
+	value, err := p.parseScalarExpression()
+	if err != nil {
+		return nil, err
+	}
+
+	// Expect )
+	if p.curTok.Type != TokenRParen {
+		return nil, fmt.Errorf("expected ) after boundary value, got %s", p.curTok.Literal)
+	}
+	p.nextToken()
+
+	return &ast.AlterTableAlterPartitionStatement{
+		SchemaObjectName: tableName,
+		BoundaryValue:    value,
+		IsSplit:          isSplit,
+	}, nil
+}
+
 func (p *Parser) parseAlterTableDropStatement(tableName *ast.SchemaObjectName) (*ast.AlterTableDropTableElementStatement, error) {
 	// Consume DROP
 	p.nextToken()