Just like LENGTH() function, MySQL BIT_LENGTH() function is not a multi-byte safe function. As we know that the difference of the result between multi-byte safe functions, like CHAR_LENGTH() or CHARACTER_LENGTH(), and BIT_LENGTH() function especially relevant for Unicode, in which most of the characters are encoded in two bytes or relevant for UTF-8 where the number of bytes varies. It is demonstrated in the example below −
Example
mysql> Select BIT_LENGTH('tutorialspoint');
+------------------------------+
| BIT_LENGTH('tutorialspoint') |
+------------------------------+
| 112 |
+------------------------------+
1 row in set (0.00 sec)
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The above result set shows that the bit length of string ‘tutorialspoint’ is 112 because it is yet not converted to Unicode character. The following query converts it into Unicode character −
mysql> SET @A = CONVERT('tutorialspoint' USING ucs2);
Query OK, 0 rows affected (0.02 sec)
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在将字符串转换为Unicode后，结果为224而不是112，因为在Unicode中，一个字符占用2个字节，如下所示 −
mysql> Select BIT_LENGTH(@A);
+----------------+
| BIT_LENGTH(@A) |
+----------------+
| 224 |
+----------------+
1 row in set (0.00 sec)
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