为什么在MariaDB 10.1中ifnull()返回DECIMAL而不是BIGINT?
例如:
查询:
select a, ifnull(b, 1) from table;
10.0.22-MariaDB:
ifnull(b, 1)
类型为BIGINT
10.1.37-MariaDB:
ifnull(b, 1)
类型为DECIMAL
此外,在两个版本中,此查询的返回类型均相同:
select 1; //type is BIGINT
为什么ifnull()
将BIGINT
转换为DECIMAL
?
答案 0 :(得分:2)
我无法重现该问题,请参见示例:
MariaDB [test]> SELECT VERSION();
Field 1: `VERSION()`
Catalog: `def`
Database: ``
Table: ``
Org_table: ``
Type: VAR_STRING
Collation: utf8_general_ci (33)
Length: 72
Max_length: 24
Decimals: 31
Flags: NOT_NULL
+-----------------+
| VERSION() |
+-----------------+
| 10.1.38-MariaDB |
+-----------------+
1 row in set (0.00 sec)
MariaDB [test]> DROP TABLE IF EXISTS `test`;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> CREATE TABLE IF NOT EXISTS `test` (
-> `bigint` BIGINT,
-> `decimal` DECIMAL(5, 2)
-> );
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> INSERT INTO `test`
-> (`bigint`, `decimal`)
-> VALUES
-> (NULL, NULL);
Query OK, 1 row affected (0.00 sec)
MariaDB [test]> SELECT 1;
Field 1: `1`
Catalog: `def`
Database: ``
Table: ``
Org_table: ``
Type: LONGLONG
Collation: binary (63)
Length: 1
Max_length: 1
Decimals: 0
Flags: NOT_NULL BINARY NUM
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)
MariaDB [test]> SELECT
-> IFNULL(`bigint`, 1) `bigint`,
-> IFNULL(`decimal`, 1) `decimal`
-> FROM
-> `test`;
Field 1: `bigint`
Catalog: `def`
Database: ``
Table: ``
Org_table: ``
Type: LONGLONG
Collation: binary (63)
Length: 20
Max_length: 1
Decimals: 0
Flags: NOT_NULL BINARY NUM
Field 2: `decimal`
Catalog: `def`
Database: ``
Table: ``
Org_table: ``
Type: NEWDECIMAL
Collation: binary (63)
Length: 7
Max_length: 4
Decimals: 2
Flags: NOT_NULL BINARY NUM
+--------+---------+
| bigint | decimal |
+--------+---------+
| 1 | 1.00 |
+--------+---------+
1 row in set (0.00 sec)
答案 1 :(得分:0)
默认返回类型将由传递给函数的两个类型值的比较得出,返回类型有一些顺序:bigint之前的整数
TYPE (X,Y) = IFNULL(type X , type Y).
在这种情况下,小数比比bigin更通用。
我想关于Mysql的两个版本在处理默认返回类型方面都有一些更改。