From ae9cc0e2d7d322433c29c63891e8f8ba0f63171e Mon Sep 17 00:00:00 2001
From: Ti Chi Robot <ti-community-prow-bot@tidb.io>
Date: Mon, 15 May 2023 16:35:17 +0800
Subject: [PATCH] Add note about SELECT CAST(MeN AS CHAR) incompatibility 
 (#13518) (#13558)

---
 data-type-numeric.md                                    | 4 ++++
 functions-and-operators/cast-functions-and-operators.md | 8 ++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/data-type-numeric.md b/data-type-numeric.md
index 1bfa46111cdf9..26c4dfb41d50a 100644
--- a/data-type-numeric.md
+++ b/data-type-numeric.md
@@ -146,6 +146,10 @@ DOUBLE PRECISION [(M,D)] [UNSIGNED] [ZEROFILL], REAL[(M,D)] [UNSIGNED] [ZEROFILL
 >
 > As in MySQL, the `DOUBLE` data type stores approximate values. For values such as currency, it is recommended to use the `DECIMAL` type instead.
 
+> **Note:**
+>
+> When TiDB converts a double-precision floating-point number represented in scientific notation to the `CHAR` type, the result is displayed inconsistently with that in MySQL. See [Cast functions and operators](/functions-and-operators/cast-functions-and-operators.md) for details.
+
 ## Fixed-point types
 
 TiDB supports all the MySQL floating-point types, including DECIMAL, and NUMERIC. For more information, [Fixed-Point Types (Exact Value) - DECIMAL, NUMERIC in MySQL](https://dev.mysql.com/doc/refman/5.7/en/fixed-point-types.html).
diff --git a/functions-and-operators/cast-functions-and-operators.md b/functions-and-operators/cast-functions-and-operators.md
index 8642d90ff7f48..1d82c6e4b887d 100644
--- a/functions-and-operators/cast-functions-and-operators.md
+++ b/functions-and-operators/cast-functions-and-operators.md
@@ -5,7 +5,9 @@ summary: Learn about the cast functions and operators.
 
 # Cast Functions and Operators
 
-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/5.7/en/cast-functions.html) available in MySQL 5.7.
+
+## List of cast functions and operators
 
 | Name                                     | Description                      |
 | ---------------------------------------- | -------------------------------- |
@@ -13,4 +15,6 @@ TiDB supports all of the [cast functions and operators](https://dev.mysql.com/do
 | [`CAST()`](https://dev.mysql.com/doc/refman/5.7/en/cast-functions.html#function_cast) | Cast a value as a certain type   |
 | [`CONVERT()`](https://dev.mysql.com/doc/refman/5.7/en/cast-functions.html#function_convert) | Cast a value as a certain type   |
 
-Cast functions and operators enable conversion of values from one data type to another.
+> **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`.