Oracle 5.0, Справочное руководство

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Precision Math Examples
1009
+------------+
| VERSION() |
+------------+
| 4.1.18-log |
+------------+
1 row in set (0.01 sec)
mysql> CREATE TABLE t SELECT 2.5 AS a, 25E-1 AS b;
Query OK, 1 row affected (0.07 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> DESCRIBE t;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| a | double(3,1) | | | 0.0 | |
| b | double | | | 0 | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.04 sec)
As of MySQL 5.0.3, the approximate-value literal is evaluated using floating point, but the exact-value
literal is handled as
DECIMAL
:
mysql> SELECT VERSION();
+------------+
| VERSION() |
+------------+
| 5.0.19-log |
+------------+
1 row in set (0.17 sec)
mysql> CREATE TABLE t SELECT 2.5 AS a, 25E-1 AS b;
Query OK, 1 row affected (0.19 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> DESCRIBE t;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| a | decimal(2,1) unsigned | NO | | 0.0 | |
| b | double | NO | | 0 | |
+-------+-----------------------+------+-----+---------+-------+
2 rows in set (0.02 sec)
Example 7. If the argument to an aggregate function is an exact numeric type, the result is also an
exact numeric type, with a scale at least that of the argument.
Consider these statements:
mysql> CREATE TABLE t (i INT, d DECIMAL, f FLOAT);
mysql> INSERT INTO t VALUES(1,1,1);
mysql> CREATE TABLE y SELECT AVG(i), AVG(d), AVG(f) FROM t;
Before MySQL 5.0.3, the result is a double no matter the argument type:
mysql> DESCRIBE y;
+--------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+-------+
| AVG(i) | double(17,4) | YES | | NULL | |
| AVG(d) | double(17,4) | YES | | NULL | |
| AVG(f) | double | YES | | NULL | |
+--------+--------------+------+-----+---------+-------+
As of MySQL 5.0.3, the result is a double only for the floating-point argument. For exact type
arguments, the result is also an exact type:
mysql> DESCRIBE y;
+--------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |