Update time-to-live.md

Co-authored-by: Lilian Lee <[email protected]>

time-to-live.md

@@ -265,7 +265,7 @@ Currently, the TTL feature has the following limitations:
         - `VARBINARY(N)`
         - `BIT(N)`
     - The character set of the first column of the primary key or composite primary key is `utf8` or `utf8mb4`, and the collation is `utf8_bin`, `utf8mb4_bin`, or `utf8mb4_0900_bin`.
-    - For tables where the primary key column type is `utf8` or `utf8mb4`, subtasks are split only based on the range of visible ASCII characters. If many primary key values have the same ASCII prefix, it might cause uneven task splitting.
+    - For tables where the character set type of the first column of the primary key is `utf8` or `utf8mb4`, subtasks are split only based on the range of visible ASCII characters. If many primary key values have the same ASCII prefix, it might cause uneven task splitting.
     - For tables that do not support splitting a TTL job into multiple subtasks, the TTL job will be executed sequentially on a single TiDB node. If the table contains a large amount of data, the execution of the TTL job might become slow.
 
 ## FAQs