cached table: add links (#18000)

cached-tables.md

@@ -33,8 +33,6 @@ This section describes the usage of cached tables by examples.
 
 Suppose that there is a table `users`:
 
-{{< copyable "sql" >}}
-
 ```sql
 CREATE TABLE users (
     id BIGINT,
@@ -45,8 +43,6 @@ CREATE TABLE users (
 
 To set this table to a cached table, use the `ALTER TABLE` statement:
 
-{{< copyable "sql" >}}
-
 ```sql
 ALTER TABLE users CACHE;
 ```
@@ -59,8 +55,6 @@ Query OK, 0 rows affected (0.01 sec)
 
 To verify a cached table, use the `SHOW CREATE TABLE` statement. If the table is cached, the returned result contains the `CACHED ON` attribute:
 
-{{< copyable "sql" >}}
-
 ```sql
 SHOW CREATE TABLE users;
 ```
@@ -78,9 +72,7 @@ SHOW CREATE TABLE users;
 1 row in set (0.00 sec)
 ```
 
-After reading data from a cached table, TiDB loads the data in memory. You can use the `trace` statement to check whether the data is loaded into memory. When the cache is not loaded, the returned result contains the `regionRequest.SendReqCtx` attribute, which indicates that TiDB reads data from TiKV.
-
-{{< copyable "sql" >}}
+After reading data from a cached table, TiDB loads the data in memory. You can use the [`TRACE`](/sql-statements/sql-statement-trace.md) statement to check whether the data is loaded into memory. When the cache is not loaded, the returned result contains the `regionRequest.SendReqCtx` attribute, which indicates that TiDB reads data from TiKV.
 
 ```sql
 TRACE SELECT * FROM users;
@@ -106,9 +98,7 @@ TRACE SELECT * FROM users;
 12 rows in set (0.01 sec)
 ```
 
-After executing `trace` again, the returned result no longer contains the `regionRequest.SendReqCtx` attribute, which indicates that TiDB no longer reads data from TiKV but reads data from the memory instead.
-
-{{< copyable "sql" >}}
+After executing [`TRACE`](/sql-statements/sql-statement-trace.md) again, the returned result no longer contains the `regionRequest.SendReqCtx` attribute, which indicates that TiDB no longer reads data from TiKV but reads data from the memory instead.
 
 ```sql
 +----------------------------------------+-----------------+------------+
@@ -127,8 +117,6 @@ After executing `trace` again, the returned result no longer contains the `regio
 
 Note that the `UnionScan` operator is used to read the cached tables, so you can see `UnionScan` in the execution plan of the cached tables through `explain`:
 
-{{< copyable "sql" >}}
-
 ```sql
 +-------------------------+---------+-----------+---------------+--------------------------------+
 | id                      | estRows | task      | access object | operator info                  |
@@ -144,8 +132,6 @@ Note that the `UnionScan` operator is used to read the cached tables, so you can
 
 Cached tables support data writes. For example, you can insert a record into the `users` table:
 
-{{< copyable "sql" >}}
-
 ```sql
 INSERT INTO users(id, name) VALUES(1001, 'Davis');
 ```
@@ -154,8 +140,6 @@ INSERT INTO users(id, name) VALUES(1001, 'Davis');
 Query OK, 1 row affected (0.00 sec)
 ```
 
-{{< copyable "sql" >}}
-
 ```sql
 SELECT * FROM users;
 ```
@@ -201,8 +185,6 @@ Create Table: CREATE TABLE `table_cache_meta` (
 >
 > Executing DDL statements on a cached table will fail. Before executing DDL statements on a cached table, you need to remove the cache attribute first and set the cached table back to a normal table.
 
-{{< copyable "sql" >}}
-
 ```sql
 TRUNCATE TABLE users;
 ```
@@ -211,8 +193,6 @@ TRUNCATE TABLE users;
 ERROR 8242 (HY000): 'Truncate Table' is unsupported on cache tables.
 ```
 
-{{< copyable "sql" >}}
-
 ```sql
 mysql> ALTER TABLE users ADD INDEX k_id(id);
 ```
@@ -223,8 +203,6 @@ ERROR 8242 (HY000): 'Alter Table' is unsupported on cache tables.
 
 To revert a cached table to a normal table, use `ALTER TABLE t NOCACHE`:
 
-{{< copyable "sql" >}}
-
 ```sql
 ALTER TABLE users NOCACHE;
 ```