Equivalent of varchar(max) in MySQL?

Question

What is the equivalent of varchar(max) in MySQL?

Answer 1

The max length of a varchar is subject to the max row size in MySQL, which is 64KB (not counting BLOBs):

VARCHAR(65535)

However, note that the limit is lower if you use a multi-byte character set:

VARCHAR(21844) CHARACTER SET utf8

Answer 2

The amount of data that a column Microsoft SQL server versions prior to version 2005 was limited to 8KB. In order to store more than 8KB you were would have had to use TEXT, NTEXT, or BLOB columns types, these column types stored their data as a collection of 8K pages separate from the the table data pages; they supported storing up to 2GB per row. The 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)

In 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. As 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.

So 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), MySql does not have an equivalent idiom.

In 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.

Answer 3

The max length of a varchar is

65535

divided 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).

minus 2 bytes to store the length

minus the length of all the other columns

minus 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.