Oracle 5.0, Справочное руководство

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Storage Requirements for Numeric Types
859
the user, then a “hidden” primary key will be created by
NDB
. This hidden primary key consumes 31-35
bytes per table record.
You may find the
ndb_size.pl
utility to be useful for estimating
NDB
storage requirements. This
Perl script connects to a current MySQL (non-Cluster) database and creates a report on how much
space that database would require if it used the
NDBCLUSTER
storage engine. See Section 17.4.18,
“
ndb_size.pl
— NDBCLUSTER Size Requirement Estimator” , for more information.
Storage Requirements for Numeric Types
Data Type Storage Required
TINYINT
1 byte
SMALLINT
2 bytes
MEDIUMINT
3 bytes
INT
,
INTEGER
4 bytes
BIGINT
8 bytes
FLOAT(p)
4 bytes if 0 <=
p
<= 24, 8 bytes if 25 <=
p
<= 53
FLOAT
4 bytes
DOUBLE [PRECISION]
,
REAL
8 bytes
DECIMAL(M,D)
,
NUMERIC(M,D)
Varies; see following discussion
BIT(M)
approximately (
M
+7)/8 bytes
The storage requirements for
DECIMAL
(and
NUMERIC
) are version-specific:
As of MySQL 5.0.3, values for
DECIMAL
columns are represented using a binary format that packs nine
decimal (base 10) digits into four bytes. Storage for the integer and fractional parts of each value are
determined separately. Each multiple of nine digits requires four bytes, and the “leftover” digits require
some fraction of four bytes. The storage required for excess digits is given by the following table.
Leftover Digits Number of Bytes
0 0
1 1
2 1
3 2
4 2
5 3
6 3
7 4
8 4
Before MySQL 5.0.3,
DECIMAL
columns are represented as strings and storage requirements are:
M
+2
bytes if
D
> 0,
M+1
bytes if
D
= 0,
D
+2 if
M < D
Storage Requirements for Date and Time Types
Data Type Storage Required
DATE
3 bytes
TIME
3 bytes
DATETIME
8 bytes
TIMESTAMP
4 bytes