In MySQL 4.1 the length is always 1 byte. In MySQL 5.0 the length may be either 1 byte (for up to 255) or 2 bytes (for 256 to 65535). 大概意思就是说: 在MySQL 4.1以前,长度总是1个字节(varchar(20),指的是20字节) 在MySQL 5.0以后,长度可以是1字节(最多255个字节)或2个字节(256到655...
CHARACTER_MAXIMUM_LENGTH的值,要求改表后要大于等于改表前的值 CHARACTER_OCTET_LENGTH的值,要求改表前后这个值要么是都小于等于 255,要么是都大于 255 除DATA_TYPE/COLUMN_TYPE/CHARACTER_MAXIMUM_LENGTH/CHARACTER_OCTET_LENGTH字段外的其余字段要求改表前后保持一致 问题一:默认值问题 我们发现,如果还改了字段名、...
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions. 看到这里,你以为上面的varchar长度是: 65535 /2=32767? 不对,因为官方文档后面又说: In contrast to CHAR, VARCHAR ...
When in-memory internal temporary tables are managed by the MEMORY storage engine, fixed-length row format is used. VARCHAR and VARBINARY column values are padded to the maximum column length, in effect storing them as CHAR and BINARY columns. 可喜的是,从 MySQL 8.0 开始,内存临时表支持 TempTabl...
In-memory temporary tablesaremanagedbythe MEMORY storage engine, which uses fixed-lengthrowformat.VARCHARandVARBINARYcolumnvaluesarepaddedtothe maximumcolumnlength,ineffect storing themasCHARandBINARYcolumns. 当临时表中的varchar被分配成最大值的char,如果存储的字符串占用空间很少,则会出现浪费 ...
除DATA_TYPE/COLUMN_TYPE/CHARACTER_MAXIMUM_LENGTH/CHARACTER_OCTET_LENGTH字段外的其余字段要求改表前后保持一致 问题一:默认值问题 我们发现,如果还改了字段名、注释、默认值这种元数据信息,依旧是可以快速改表,于是乎就进行了优化,不再比较这三个属性COLUMN_NAME|COLUMN_COMMENT|COLUMN_DEFAULT。
Values inVARCHARcolumns are variable-length strings. The length can be specified as a value from 0 to 65,535. The effective maximum length of aVARCHARis subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used. ...
whichusesfixed-lengthrowformat.VARCHARandVARBINARYcolumnvaluesarepaddedtothemaximumcolumnlength,ineffect...
In-memorytemporarytablesare managedbythe MEMORY storageengine,which usesfixed-lengthrowformat.VARCHARandVARBINARYcolumnvaluesare paddedtothe maximumcolumnlength,ineffect storing themasCHARandBINARYcolumns. 当临时表中的varchar被分配成最大值的char,如果存储的字符串占用空间很少,则会出现浪费 ...
在 MySQL 中，VARCHAR 类型的长度默认是最大为 65535 个字符（字节），但是实际存储的最大长度受到多种...