fix ctc doc (#5914) (#5953)

pingcap · Jul 8, 2021 · 98989b5 · 98989b5
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diff --git a/sql-statements/sql-statement-alter-table.md b/sql-statements/sql-statement-alter-table.md
@@ -149,9 +149,15 @@ Query OK, 0 rows affected, 1 warning (0.25 sec)
 
 The following major restrictions apply to `ALTER TABLE` in TiDB:
 
-* Multiple operations cannot be completed in a single `ALTER TABLE` statement.
+* Making multiple changes in a single `ALTER TABLE` statement is currently not supported. 
 
-* Lossy changes such as changing from `BIGINT` to `INT` are currently not supported.
+* Changes of the [Reorg-Data](/sql-statements/sql-statement-modify-column.md#reorg-data-change) types on primary key columns are not supported.
+
+* Changes of column types on partitioned tables are not supported.
+
+* Changes of column types on generated columns are not supported.
+
+* Changes of some data types (for example, some TIME, Bit, Set, Enum, and JSON types) are not supported due to the compatibility issues of the `CAST` function's behavior between TiDB and MySQL.
 
 * Spatial data types are not supported.
 

diff --git a/sql-statements/sql-statement-change-column.md b/sql-statements/sql-statement-change-column.md
@@ -151,11 +151,11 @@ ERROR 8200 (HY000): Unsupported modify column: change from original type decimal
 
 ## MySQL compatibility
 
-* Making multiple changes in a single `ALTER TABLE` statement is not currently supported.
-* Changes of data types on primary key columns are not supported.
+* Making multiple changes in a single `ALTER TABLE` statement is currently not supported.
+* Changes of [Reorg-Data](/sql-statements/sql-statement-modify-column.md#reorg-data-change) types on primary key columns are not supported.
 * Changes of column types on partitioned tables are not supported.
-* Changes of column types on the generated columns are not supported.
-* Changes of some data types (for example, some TIME types, Bit, Set, Enum, JSON) are not supported due to some compatibility issues of the `cast` function's behavior between TiDB and MySQL.
+* Changes of column types on generated columns are not supported.
+* Changes of some data types (for example, some TIME, Bit, Set, Enum, and JSON types) are not supported due to the compatibility issues of the `CAST` function's behavior between TiDB and MySQL.
 
 ## See also
 

diff --git a/sql-statements/sql-statement-modify-column.md b/sql-statements/sql-statement-modify-column.md
@@ -177,15 +177,21 @@ CREATE TABLE `t1` (
     ERROR 1105 (HY000): Unsupported multi schema change
     ```
 
-* Does not support modifying the data types on the primary key columns. For example:
+* Does not support modifying the Reorg-Data types on the primary key columns but supports modifying the Meta-Only types. For example:
 
     ```sql
     CREATE TABLE t (a int primary key);
     ALTER TABLE t MODIFY COLUMN a VARCHAR(10);
     ERROR 8200 (HY000): Unsupported modify column: column has primary key flag
     ```
 
-* Does not support modifying the types of generate columns. For example:
+    ```sql
+    CREATE TABLE t (a int primary key);
+    ALTER TABLE t MODIFY COLUMN a bigint;
+    Query OK, 0 rows affected (0.01 sec)
+    ```
+
+* Does not support modifying the column types on generated columns. For example:
 
     ```sql
     CREATE TABLE t (a INT, b INT as (a+1));