Add DISTRIBUTION option support for CREATE EXTERNAL TABLE

- Add ExternalTableDistributionOption AST type
- Add ExternalTableShardedDistributionPolicy for SHARDED(col)
- Add ExternalTableRoundRobinDistributionPolicy for ROUND_ROBIN
- Add ExternalTableReplicatedDistributionPolicy for REPLICATE
- Add parsing and marshaling for all distribution policies

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

Author: kyleconroy

ast/external_statements.go

@@ -95,6 +95,36 @@ type ExternalTableRejectTypeOption struct {
 
 func (o *ExternalTableRejectTypeOption) externalTableOptionItem() {}
 
+// ExternalTableDistributionPolicy is the interface for distribution policies
+type ExternalTableDistributionPolicy interface {
+	externalTableDistributionPolicy()
+}
+
+// ExternalTableDistributionOption represents a DISTRIBUTION option
+type ExternalTableDistributionOption struct {
+	OptionKind string
+	Value      ExternalTableDistributionPolicy
+}
+
+func (o *ExternalTableDistributionOption) externalTableOptionItem() {}
+
+// ExternalTableShardedDistributionPolicy represents SHARDED distribution
+type ExternalTableShardedDistributionPolicy struct {
+	ShardingColumn *Identifier
+}
+
+func (p *ExternalTableShardedDistributionPolicy) externalTableDistributionPolicy() {}
+
+// ExternalTableRoundRobinDistributionPolicy represents ROUND_ROBIN distribution
+type ExternalTableRoundRobinDistributionPolicy struct{}
+
+func (p *ExternalTableRoundRobinDistributionPolicy) externalTableDistributionPolicy() {}
+
+// ExternalTableReplicatedDistributionPolicy represents REPLICATE distribution
+type ExternalTableReplicatedDistributionPolicy struct{}
+
+func (p *ExternalTableReplicatedDistributionPolicy) externalTableDistributionPolicy() {}
+
 // ExternalTableOption represents a simple option for external table (legacy)
 type ExternalTableOption struct {
 	OptionKind string

parser/marshal.go

@@ -16697,6 +16697,8 @@ func externalTableOptionItemToJSON(opt ast.ExternalTableOptionItem) jsonNode {
 		return externalTableLiteralOrIdentifierOptionToJSON(o)
 	case *ast.ExternalTableRejectTypeOption:
 		return externalTableRejectTypeOptionToJSON(o)
+	case *ast.ExternalTableDistributionOption:
+		return externalTableDistributionOptionToJSON(o)
 	default:
 		return jsonNode{}
 	}
@@ -16710,6 +16712,34 @@ func externalTableRejectTypeOptionToJSON(opt *ast.ExternalTableRejectTypeOption)
 	}
 }
 
+func externalTableDistributionOptionToJSON(opt *ast.ExternalTableDistributionOption) jsonNode {
+	node := jsonNode{
+		"$type":      "ExternalTableDistributionOption",
+		"OptionKind": opt.OptionKind,
+	}
+	if opt.Value != nil {
+		switch v := opt.Value.(type) {
+		case *ast.ExternalTableShardedDistributionPolicy:
+			policyNode := jsonNode{
+				"$type": "ExternalTableShardedDistributionPolicy",
+			}
+			if v.ShardingColumn != nil {
+				policyNode["ShardingColumn"] = identifierToJSON(v.ShardingColumn)
+			}
+			node["Value"] = policyNode
+		case *ast.ExternalTableRoundRobinDistributionPolicy:
+			node["Value"] = jsonNode{
+				"$type": "ExternalTableRoundRobinDistributionPolicy",
+			}
+		case *ast.ExternalTableReplicatedDistributionPolicy:
+			node["Value"] = jsonNode{
+				"$type": "ExternalTableReplicatedDistributionPolicy",
+			}
+		}
+	}
+	return node
+}
+
 func externalTableColumnDefinitionToJSON(col *ast.ExternalTableColumnDefinition) jsonNode {
 	node := jsonNode{
 		"$type": "ExternalTableColumnDefinition",

parser/parse_statements.go

@@ -8567,6 +8567,30 @@ func (p *Parser) parseCreateExternalTableStatement() (*ast.CreateExternalTableSt
 						p.nextToken()
 					}
 					stmt.ExternalTableOptions = append(stmt.ExternalTableOptions, opt)
+				case "DISTRIBUTION":
+					// Parse DISTRIBUTION = SHARDED(col), ROUND_ROBIN, or REPLICATE
+					distVal := strings.ToUpper(p.curTok.Literal)
+					p.nextToken()
+					opt := &ast.ExternalTableDistributionOption{
+						OptionKind: "Distribution",
+					}
+					if distVal == "SHARDED" {
+						if p.curTok.Type == TokenLParen {
+							p.nextToken() // consume (
+							sharded := &ast.ExternalTableShardedDistributionPolicy{
+								ShardingColumn: p.parseIdentifier(),
+							}
+							if p.curTok.Type == TokenRParen {
+								p.nextToken() // consume )
+							}
+							opt.Value = sharded
+						}
+					} else if distVal == "ROUND_ROBIN" {
+						opt.Value = &ast.ExternalTableRoundRobinDistributionPolicy{}
+					} else if distVal == "REPLICATE" {
+						opt.Value = &ast.ExternalTableReplicatedDistributionPolicy{}
+					}
+					stmt.ExternalTableOptions = append(stmt.ExternalTableOptions, opt)
 				case "LOCATION", "FILE_FORMAT", "TABLE_OPTIONS":
 					opt := &ast.ExternalTableLiteralOrIdentifierOption{
 						Value: &ast.IdentifierOrValueExpression{},