fixed the given examples of nullable in zh doc

docs/zh/data_types/nullable.md

@@ -19,37 +19,21 @@
 
 ## 用法示例
 
+
+```sql
+CREATE TABLE t_null(x Int8, y Nullable(Int8)) ENGINE TinyLog
 ```
-:) CREATE TABLE t_null(x Int8, y Nullable(Int8)) ENGINE TinyLog
+```sql
-
+INSERT INTO t_null VALUES (1, NULL), (2, 3)
-CREATE TABLE t_null
+```
-(
+```sql
-    x Int8,
+SELECT x + y FROM t_null
-    y Nullable(Int8)
+```
-)
+```text
-ENGINE = TinyLog
-
-Ok.
-
-0 rows in set. Elapsed: 0.012 sec.
-
-:) INSERT INTO t_null VALUES (1, NULL)
-
-INSERT INTO t_null VALUES
-
-Ok.
-
-1 rows in set. Elapsed: 0.007 sec.
-
-:) SELECT x + y FROM t_null
-
-SELECT x + y
-FROM t_null
-
 ┌─plus(x, y)─┐
 │       ᴺᵁᴸᴸ │
 │          5 │
 └────────────┘
-
-2 rows in set. Elapsed: 0.144 sec.
 ```
+
+[来源文章](https://clickhouse.yandex/docs/en/data_types/nullable/) <!--hide-->