MySql varchar length for emojis on Sequel Pro

Question

I'm using MySql version 5.6.46 on Linux. I have a column name varchar(50) COLLATE utf8mb4_bin and ENGINE=InnoDB DEFAULT CHARSET=utf8mb4.

When I tried to insert some data into the table. I find that,

for a (1 byte in utf8), it can store 50 maximum.

for 爱 (3 bytes in utf8, Chinese character love), it can store 50 maximum.

for (4 bytes in utf8, hex F09F9881), it can store 25 maximum.

This confuses me. Why Mysql is not treating one emoji as one character? If Mysql does the byte-count limit and improperly uses 3-byte-per-character, I'm expecting it can store 50*3/4=37. How on earth Mysql do the restriction?

----------UPDATE-------------

Thanks to your response, I figure it out. I am on MacOS X and I was using Sequel Pro 1.1.2. When I edit table content in the UI of the software, the maximum is 25 emoji and it toasts warning maximum text length is set to 50

Then I tried the raw hex approach on the server set name = X'F09F9881...F09F9881' and it can hold 50 emojis perfectly.

So this is a Sequel Pro issue. I will add Sequel Pro tag to this question. Hope this will help people who met the same issue. Thanks

Answer 1

No arithmetic needed.

varchar(50)

Holds 50 characters of any type. This will occupy up to 202 bytes (4 * 50 + 2 for a hidden length field).

To debug your situation, please provide:

SELECT VARIABLES LIKE 'char%';

SELECT col, HEX(col) FROM ...  -- to show what was stored.