Specifications

A summary of possible identifiers is shown in Table 8.4. The only additional exception is that

you cannot use ASCII(0) or ASCII(255) in identifiers (and to be honest, I’m not sure why

you’d want to).

TABLE 8.4 MySQL Identifiers

Max Case Characters

Type Length Sensitive? Allowed

Database 64 same as O/S Anything allowed in a directory name in

your O/S except the / character

Table 64 same as O/S Anything allowed in a filename in your

O/S except the / and . characters

Column 64 no Anything

Alias 255 no Anything

These rules are extremely open.

As of MySQL 3.23.6, you can even have reserved words and special characters of all kinds in

identifiers, the only limitation being that if you use anything weird like this, you have to put it

in back quotes (located under the tilde key on the top left of most keyboards). For example

create database `create database`;

The rules in versions of MySQL (prior to 3.23.6) are more restrictive, and don’t allow you to

do this.

Of course, you should apply common sense to all this freedom. Just because you can call a

database `create database`, it doesn’t that mean that you should. The same principle applies

as in any other kind of programming—use meaningful identifiers.

Column Data Types

The three basic column types in MySQL are: numeric, date and time, and string. Within each

of these categories are a large number of types. We’ll summarize them here, and go into more

detail about the strengths and weaknesses of each in Chapter 11.

Each of the three types comes in various storage sizes. When choosing a column type, the prin-

ciple is generally to choose the smallest type that your data will fit into.

For many data types, when you are creating a column of that type, you can specify the maxi-

mum display length. This is shown in the following tables of data types as M. If it’s optional for

that type, it is shown in square brackets. The maximum value you can specify for M is 255.

Optional values throughout these descriptions are shown in square brackets.

Using MySQL

ART II

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