special case for unix timestamp

Author: James Cor

enginetest/queries/queries.go

@@ -10218,6 +10218,20 @@ from typestable`,
 			{"     └─ name: "},
 		},
 	},
+
+	// check that string timestamps preserve trailing 0s
+	{
+		Query:    "select unix_timestamp('2001-02-03 12:34:56.10');",
+		Expected: []sql.Row{
+			{"981228896.10"},
+		},
+	},
+	{
+		Query:    "select unix_timestamp('2001-02-03 12:34:56.000000');",
+		Expected: []sql.Row{
+			{"981228896.000000"},
+		},
+	},
 }
 
 var KeylessQueries = []QueryTest{

sql/expression/function/date.go

@@ -476,6 +476,22 @@ func NewUnixTimestamp(args ...sql.Expression) (sql.Expression, error) {
 	if err != nil || date == nil {
 		return &UnixTimestamp{Date: arg}, nil
 	}
+	// special case: text types with fractional seconds preserve scale
+	if types.IsText(arg.Type()) {
+		dateStr := date.(string)
+		idx := strings.Index(dateStr, ".")
+		if idx != -1 {
+			dateStr = strings.TrimSpace(dateStr[idx:])
+			scale := uint8(len(dateStr) - 1)
+			if scale > 0 {
+				typ, tErr := types.CreateDecimalType(19, scale)
+				if tErr != nil {
+					return nil, tErr
+				}
+				return &UnixTimestamp{Date: arg, typ: typ}, nil
+			}
+		}
+	}
 	date, _, err = types.DatetimeMaxPrecision.Convert(date)
 	if err != nil {
 		return &UnixTimestamp{Date: arg}, nil