我有一个包含253个字符的字符串，但是由于某些字符超过一个字节（在本例中，它包含几个零宽度的空格），它占用了261个字节。
我想把这个字符串插入一个 VARCHAR(255) a列 utf8mb4 表，但它抛出以下错误：

INSERT INTO mytable(mycolumn) VALUES("This string contains 253 ​characters which should ​fit inside of a varchar(255) column, but because ​of the zero width spaces, it takes up more than 255 bytes and therefore throws an error when you try to insert it into the table and that makes me ​sad.")

/*Error 1406: Data too long for column*/

下面是两个长度函数输出的示例：

/* Returns 253 */
SELECT CHAR_LENGTH("This string contains 253 ​characters which should ​fit inside of a varchar(255) column, but because ​of the zero width spaces, it takes up more than 255 bytes and therefore throws an error when you try to insert it into the table and that makes me ​sad.");

/* Returns 261 */
SELECT LENGTH("This string contains 253 ​characters which should ​fit inside of a varchar(255) column, but because ​of the zero width spaces, it takes up more than 255 bytes and therefore throws an error when you try to insert it into the table and that makes me ​sad.");

要解决这个问题，我需要删掉足够的字符，使字符串在字节限制内。
不幸的是 LEFT() 函数似乎不适用于此：

/* Still returns 261 because it counts characters, not bytes */
SELECT LENGTH(LEFT("This string contains 253 ​characters which should ​fit inside of a varchar(255) column, but because ​of the zero width spaces, it takes up more than 255 bytes and therefore throws an error when you try to insert it into the table and that makes me ​sad.", 255));

那么，我怎样才能把绳子剪下来呢？