Database Reference
In-Depth Information
TIMESTAMP options
Starting with MySQL 4.1.2, there are more options that can affect a
TIMESTAMP
column. Let's add to our
book
table, a column named
stamp
of type
TIMESTAMP
.
In the
Default
drop-down, we could choose
CURRENT_TIMESTAMP
;
but we
won't for this exercise. However in the
Attributes
column, we choose
on update
CURRENT_TIMESTAMP
.
Bit
MySQL 5.0.3 introduced true bit-field values. These take the same amount of space in
the database as the number of bits in their definition. Let's say we have three pieces
of information about each book, and each piece can only be true (1) or false (0):
•
Book is hard cover
•
Book contains a CD-ROM
•
Book is available only in electronic format
We'll use a single
BIT
field to store these three pieces of information. Therefore, we
add a field having a length of
3
(which means 3 bits) to the
book
table:
To construct and subsequently interpret the values we store in this field, we have to
think in binary, respecting the position of each bit within the field. To indicate that a
book is hard cover, does not contain a CD-ROM, and is available only in electronic
format, we would use a value of
101
.
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