Databases Reference
In-Depth Information
FLOAT[(width, decimals)] [UNSIGNED] [ZEROFILL]
or
FLOAT[(precision)] [UNSIGNED]
[ZEROFILL]
Stores floating-point numbers. It has two optional syntaxes: the first allows an
optional number of
decimals
and an optional display
width
, and the second allows
an optional
precision
that controls the accuracy of the approximation measured
in bits. Without parameters, the type stores small, four-byte, single-precision
floating-point values; usually, you use it without providing any parameters. When
precision
is between 0 and 24, the default behavior occurs. When
precision
is
between 25 and 53, the type behaves as for
DOUBLE
. The
width
has no effect on what
is stored, only on what is displayed. The
UNSIGNED
and
ZEROFILL
options behave as
for
INT
.
DOUBLE[(
width
,
decimals
)] [UNSIGNED] [ZEROFILL]
Stores floating-point numbers. It has one optional syntax: it allows an optional
number of
decimals
and an optional display
width
. Without parameters, the type
stores normal, eight-byte, double-precision floating point values; usually, you use
it without providing any parameters. The
width
has no effect on what is stored,
only on what is displayed. The
UNSIGNED
and
ZEROFILL
options behave as for
INT
.
The
DOUBLE
type has two identical synonyms:
REAL
and
DOUBLE PRECISION
. The
REAL
alternative can be made to behave as
FLOAT
using a nondefault parameter to
the MySQL server, but this is not discussed here.
Other date and time types
We discussed the
DATE
,
TIME
, and
TIMESTAMP
types in “Common column types.” There
are two more date and time types:
YEAR
for storing only year values, and
DATETIME
for
storing date and time combinations without the automatic-update feature of
TIMESTAMP
. These work as follows:
YEAR[(
digits
)]
Stores a two- or four-digit year, depending on whether
2
or
4
is passed as the op-
tional
digits
parameter. Without the parameter, four digits is the default. The two-
digit version stores values from 70 to 69, representing 1970 to 2069; again, we
caution against using two-digit dates. The four-digit version stores values in the
range 1901 to 2155, as well as the
zero year
, 0000. Illegal values are converted to
the zero date. You can input year values as either strings (such as
'2005'
) or integers
(such as
2005
). The
YEAR
type requires one byte of storage space.
DATETIME
Stores and displays a date and time pair in the format
YYYY-MM-DD HH:MM:SS
for the
range
1000-01-01 00:00:00
to
9999-12-31 23:59:59
. As for
TIMESTAMP
, the value
stored always matches the template
YYYY-MM-DD HH:MM:SS
, but the value can be
input in the same formats listed for the
TIMESTAMP
description. If you assign only a
date to a
DATETIME
column, the zero time
00:00:00
is assumed. If you assign only a
time to a
DATETIME
column, the zero date
0000-00-00
is assumed. This type does
not have the automatic update features of
TIMESTAMP
.
