Question about the maximum length of varchar in MySQL _ MySQL

About the maximum length of varchar in MySQL bitsCN.com
I was asked a question: What is the maximum varchar length in MySQL? This is not a fixed number. This article briefly describes the restrictions.
1. restrictions on rule fields the following rules apply when defining a field: a) the storage restriction varchar field stores the actual content separately in the clustered index, the content must start with 1 to 2 bytes to indicate the actual length (2 bytes if the length exceeds 255). Therefore, the maximum length cannot exceed 65535. B) encoding length: if the character type is gbk, each character occupies up to 2 bytes, and the maximum length cannot exceed 32766. if the character type is utf8, each character occupies up to 3 bytes, the maximum length cannot exceed 21845. If the preceding limits are exceeded during definition, the varchar field is forcibly converted to the text type and generates a warning. C) the length of a line is limited by the length defined by a line in practice. MySQL requires that the definition length of a row cannot exceed 65535. If the defined table length exceeds this value, ERROR 1118 (42000): Row size too large is displayed. the maximum row size for the used table type, not counting BLOBs, it is 65535. you have to change some columns to TEXT or BLOBs. 2. here are two examples to illustrate the calculation of the actual length. A) If a table has only one varchar type, such as create table t4 (c varchar (N) charset = gbk, the maximum value of N here is (65535-1-2) /2 = 32766. The reason for the decrease of 1 is that the actual row storage starts from the second byte. the reason for the decrease of 2 is that the two bytes in the varchar header indicate the length. the reason for the decrease of 2 is that the character encoding is gbk. B) if a table is defined as create table t4 (c int, c2 char (30), c3 varchar (N) charset = utf8; the maximum value of N here is (65535-1-2-4-30*3)/3 = 21812 minus 1 and minus 2 is the same as that in the previous example; the reason for 4 reduction is that c of the int type occupies 4 bytes; the reason for 30*3 reduction is that char (30) occupies 90 bytes and the encoding is utf8. If varchar exceeds the preceding B rule and is forced to be of the text type, each field occupies 11 bytes. of course, this is no longer a "varchar. Author: Ding Lin .tbbitsCN.com