cast-functions-and-operators: Update reference manual links

functions-and-operators/cast-functions-and-operators.md

@@ -6,16 +6,67 @@ aliases: ['/docs/dev/functions-and-operators/cast-functions-and-operators/','/do
 
 # Cast Functions and Operators
 
-Cast functions and operators enable conversion of values from one data type to another. TiDB supports all of the [cast functions and operators](https://dev.mysql.com/doc/refman/5.7/en/cast-functions.html) available in MySQL 5.7.
+Cast functions and operators enable conversion of values from one data type to another. TiDB supports all of the [cast functions and operators](https://dev.mysql.com/doc/refman/8.0/en/cast-functions.html) available in MySQL 8.0.
 
 ## List of cast functions and operators
 
 | Name                                     | Description                      |
 | ---------------------------------------- | -------------------------------- |
-| [`BINARY`](https://dev.mysql.com/doc/refman/8.0/en/cast-functions.html#operator_binary) | Cast a string to a binary string |
+| [`BINARY`](https://dev.mysql.com/doc/refman/8.0/en/cast-functions.html#operator_binary) | Cast a string to a binary string. |
 | [`CAST()`](https://dev.mysql.com/doc/refman/8.0/en/cast-functions.html#function_cast) | Cast a value as a certain type   |
 | [`CONVERT()`](https://dev.mysql.com/doc/refman/8.0/en/cast-functions.html#function_convert) | Cast a value as a certain type   |
 
 > **Note:**
 >
 > TiDB and MySQL display inconsistent results for `SELECT CAST(MeN AS CHAR)` (or its equivalent form `SELECT CONVERT(MeM, CHAR)`), where `MeN` represents a double-precision floating-point number in scientific notation. MySQL displays the complete numeric value when `-15 <= N <= 14` and the scientific notation when `N < -15` or `N > 14`. However, TiDB always displays the complete numeric value. For example, MySQL displays the result of `SELECT CAST(3.1415e15 AS CHAR)` as `3.1415e15`, while TiDB displays the result as `3141500000000000`.
+
+### BINARY
+
+The `BINARY` operator has been deprecated in MySQL 8.0.27. It is recommended to use `CAST(... AS BINARY)` instead both in TiDB and MySQL.
+
+### CAST
+
+The `CAST()` function cast an expression to a specific type.
+
+This function is also used to create [Multi-valued Indexes](/sql-statements/sql-statement-create-index.md#multi-valued-indexes).
+
+Example:
+
+```sql
+SELECT CAST(0x54694442 AS CHAR);
+```
+
+```
++--------------------------+
+| CAST(0x54694442 AS CHAR) |
++--------------------------+
+| TiDB                     |
++--------------------------+
+1 row in set (0.0002 sec)
+```
+
+
+### CONVERT
+
+The `CONVERT()` function is used to convert between [character sets](/character-set-and-collation.md).
+
+Example
+
+```sql
+SELECT CONVERT(0x616263 USING utf8mb4);
+```
+
+```
++---------------------------------+
+| CONVERT(0x616263 USING utf8mb4) |
++---------------------------------+
+| abc                             |
++---------------------------------+
+1 row in set (0.0004 sec)
+```
+
+# MySQL Compatibility
+
+- TiDB doesn't support cast operations on spatial types. [GitHub Issue #6347](https://github.com/pingcap/tidb/issues/6347)
+- TiDB doesn't support `AT TIME ZONE` for `CAST()`. [GitHub Issue #51742](https://github.com/pingcap/tidb/issues/51742)
+- `CAST(24 AS YEAR)` returns 2 digits in TiDB and 4 digits in MySQL. [GitHub Issue 29629](https://github.com/pingcap/tidb/issues/29629)