Bill Karwin :
The max length of a varchar is subject to the max row size in MySQL, which is 64KB (not counting BLOBs):\n\nVARCHAR(65535)\n\n\nHowever, note that the limit is lower if you use a multi-byte character set:\n\nVARCHAR(21844) CHARACTER SET utf8\n\n\n\n\nHere are some examples:\n\nThe maximum row size is 65535, but a varchar also includes a byte or two to encode the length of a given string. So you actually can't declare a varchar of the maximum row size, even if it's the only column in the table.\n\nmysql> CREATE TABLE foo ( v VARCHAR(65534) );\nERROR 1118 (42000): Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. This includes storage overhead, check the manual. You have to change some columns to TEXT or BLOBs\n\n\nBut if we try decreasing lengths, we find the greatest length that works:\n\nmysql> CREATE TABLE foo ( v VARCHAR(65532) );\nQuery OK, 0 rows affected (0.01 sec)\n\n\nNow if we try to use a multibyte charset at the table level, we find that it counts each character as multiple bytes. UTF8 strings don't necessarily use multiple bytes per string, but MySQL can't assume you'll restrict all your future inserts to single-byte characters.\n\nmysql> CREATE TABLE foo ( v VARCHAR(65532) ) CHARSET=utf8;\nERROR 1074 (42000): Column length too big for column 'v' (max = 21845); use BLOB or TEXT instead\n\n\nIn spite of what the last error told us, InnoDB still doesn't like a length of 21845.\n\nmysql> CREATE TABLE foo ( v VARCHAR(21845) ) CHARSET=utf8;\nERROR 1118 (42000): Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. This includes storage overhead, check the manual. You have to change some columns to TEXT or BLOBs\n\n\nThis makes perfect sense, if you calculate that 21845*3 = 65535, which wouldn't have worked anyway. Whereas 21844*3 = 65532, which does work.\n\nmysql> CREATE TABLE foo ( v VARCHAR(21844) ) CHARSET=utf8;\nQuery OK, 0 rows affected (0.32 sec)\n",
2008-12-02T01:55:28
joshperry :
TLDR; MySql does not have an equivalent concept of varchar(max), this is a MS SQL Server feature.\nWhat is VARCHAR(max)?\nvarchar(max) is a feature of Microsoft SQL Server.\nThe amount of data that a column could store in Microsoft SQL server versions prior to version 2005 was limited to 8KB. In order to store more than 8KB you would have to use TEXT, NTEXT, or BLOB columns types, these column types stored their data as a collection of 8K pages separate from the table data pages; they supported storing up to 2GB per row.\nThe big caveat to these column types was that they usually required special functions and statements to access and modify the data (e.g. READTEXT, WRITETEXT, and UPDATETEXT)\nIn SQL Server 2005, varchar(max) was introduced to unify the data and queries used to retrieve and modify data in large columns. The data for varchar(max) columns is stored inline with the table data pages.\nAs the data in the MAX column fills an 8KB data page an overflow page is allocated and the previous page points to it forming a linked list. Unlike TEXT, NTEXT, and BLOB the varchar(max) column type supports all the same query semantics as other column types.\nSo varchar(MAX) really means varchar(AS_MUCH_AS_I_WANT_TO_STUFF_IN_HERE_JUST_KEEP_GROWING) and not varchar(MAX_SIZE_OF_A_COLUMN).\nMySql does not have an equivalent idiom.\nIn order to get the same amount of storage as a varchar(max) in MySql you would still need to resort to a BLOB column type. This article discusses a very effective method of storing large amounts of data in MySql efficiently.",
2008-12-02T02:49:34
ʞɔıu :
The max length of a varchar is \n\n65535\n\ndivided by the max byte length of a character in the character set the column is set to (e.g. utf8=3 bytes, ucs2=2, latin1=1).\n\nminus 2 bytes to store the length\n\nminus the length of all the other columns\n\nminus 1 byte for every 8 columns that are nullable. If your column is null/not null this gets stored as one bit in a byte/bytes called the null mask, 1 bit per column that is nullable.",
2008-12-02T03:42:42
Dinanath Parit :
For Sql Server\n\nalter table prg_ar_report_colors add Text_Color_Code VARCHAR(max);\n\nFor MySql\n\nalter table prg_ar_report_colors add Text_Color_Code longtext;\n\nFor Oracle\n\nalter table prg_ar_report_colors add Text_Color_Code CLOB;",
2016-12-02T11:18:13