Managing and Using MySQL (2nd Edition)

Chapter 16. MySQL Data Types

MySQL offers a wide variety of data types to support the storage of different kinds of data. This chapter lists the full range of these data types and describes their functionality, syntax, and data storage requirements. For each data type, the syntax shown uses square brackets ( [] ) to indicate optional parts of the syntax. The following example shows how BIGINT is explained in this chapter:

BIGINT[( display_size )]

This indicates that you can use BIGINT alone or with a display size value. The italics indicate that you do not enter display_size literally, but instead enter your own value. Thus, possible uses of BIGINT include:

BIGINT BIGINT(20)

Like the BIGINT type above, many MySQL data types support the specification of a display size. Unless otherwise specified, this value must be an integer between 1 and 255.

Table 16-1 lists the data types and categorizes them as numeric, string, date, or complex. You can find the full description of each data type later in this chapter.

Table  16-1. MySQL data types

In the following cases, MySQL silently changes the column type you specify in your table creation to something else:

VARCHAR -> CHAR

When the specified VARCHAR column size is less than four characters , it is converted to CHAR .

CHAR -> VARCHAR

When a table has at least one column of a variable length, all CHAR columns greater than three characters in length are converted to VARCHAR .

TIMESTAMP display sizes

Display sizes for TIMESTAMP fields must be an even value between 2 and 14. A display size of 0 or greater than 14 will convert the field to a display size of 14. An odd-valued display size will be converted to the next highest even value.