What is the difference between BIT and TINYINT in MySQL?
A TINYINT is an 8-bit integer value, a BIT field can store between 1 bit, BIT(1), and 64 bits, BIT(64). For a boolean values, BIT(1) is pretty common.
From Overview of Numeric Types;
BIT[(M)]
A bit-field type. M indicates the number of bits per value, from 1 to 64. The default is 1 if M is omitted.
This data type was added in MySQL 5.0.3 for MyISAM, and extended in 5.0.5 to MEMORY, InnoDB, BDB, and NDBCLUSTER. Before 5.0.3, BIT is a synonym for TINYINT(1).
TINYINT[(M)] [UNSIGNED] [ZEROFILL]
A very small integer. The signed range is -128 to 127. The unsigned range is 0 to 255.
Additionally consider this;
BOOL, BOOLEAN
These types are synonyms for TINYINT(1). A value of zero is considered false. Non-zero values are considered true.
All these theoretical discussions are great, but in reality, at least if you're using MySQL and really for SQLServer as well, it's best to stick with non-binary data for your booleans for the simple reason that it's easier to work with when you're outputting the data, querying and so on. It is especially important if you're trying to achieve interoperability between MySQL and SQLServer (i.e. you sync data between the two), because the handling of BIT datatype is different in the two of them. SO in practice you will have a lot less hassles if you stick with a numeric datatype. I would recommend for MySQL to stick with BOOL or BOOLEAN which gets stored as TINYINT(1). Even the way MySQL Workbench and MySQL Administrator display the BIT datatype isn't nice (it's a little symbol for binary data). So be practical and save yourself the hassles (and unfortunately I'm speaking from experience).
BIT should only allow 0 and 1 (and NULL, if the field is not defined as NOT NULL). TINYINT(1) allows any value that can be stored in a single byte, -128..127 or 0..255 depending on whether or not it's unsigned (the 1 shows that you intend to only use a single digit, but it does not prevent you from storing a larger value).
For versions older than 5.0.3, BIT is interpreted as TINYINT(1), so there's no difference there.
BIT has a "this is a boolean" semantic, and some apps will consider TINYINT(1) the same way (due to the way MySQL used to treat it), so apps may format the column as a check box if they check the type and decide upon a format based on that.