45个字符，数据库设计时存储IPv6需要 varchar(45)

45 characters.

You might expect an address to be

0000:0000:0000:0000:0000:0000:0000:0000

8 * 4 + 7 = 39

8 groups of 4 digits with 7 : between them.

But if you have an IPv4-mapped IPv6 address, the last two groups can be written in base 10 separated by ., eg. [::ffff:192.168.100.228]. Written out fully:

0000:0000:0000:0000:0000:ffff:192.168.100.228

(6 * 4 + 5) + 1 + (4 * 3 + 3) = 29 + 1 + 15 = 45

Note, this is an input/display convention – it’s still a 128 bit address and for storage it would probably be best to standardise on the raw colon separated format, i.e. [0000:0000:0000:0000:0000:ffff:c0a8:64e4] for the address above.