Preserve singular vs plural form for retention period units

DAY/DAYS, WEEK/WEEKS, MONTH/MONTHS, YEAR/YEARS are now mapped
to Day/Days, Week/Weeks, Month/Months, Year/Years respectively.

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

Author: kyleconroy

parser/parse_ddl.go

@@ -7231,19 +7231,25 @@ func (p *Parser) parseRetentionPeriodDefinition() (*ast.RetentionPeriodDefinitio
 		return nil, fmt.Errorf("expected number for retention period, got %s", p.curTok.Literal)
 	}
 
-	// Parse unit
+	// Parse unit - preserve singular vs plural from SQL syntax
 	unitVal := strings.ToUpper(p.curTok.Literal)
 	switch unitVal {
-	case "DAY", "DAYS":
+	case "DAY":
 		ret.Units = "Day"
-	case "WEEK", "WEEKS":
+	case "DAYS":
+		ret.Units = "Days"
+	case "WEEK":
 		ret.Units = "Week"
+	case "WEEKS":
+		ret.Units = "Weeks"
 	case "MONTH":
 		ret.Units = "Month"
 	case "MONTHS":
 		ret.Units = "Months"
-	case "YEAR", "YEARS":
+	case "YEAR":
 		ret.Units = "Year"
+	case "YEARS":
+		ret.Units = "Years"
 	default:
 		return nil, fmt.Errorf("unexpected unit %s for retention period", unitVal)
 	}

parser/testdata/Baselines140_CreateTableTests140_Azure/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/CreateTableTests140_Azure/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}