问题描述
我正在从 SQL Server 过渡到 MySQL 5.1，并且似乎在尝试使用 select 语句创建表时遇到了困难，以便该列有点.
I am transitioning from SQL Server to MySQL 5.1 and seem to be tripped up trying to create a table using a select statement so that the column is a bit.
理想情况下，以下方法可行:
Ideally the following would work:
CREATE TABLE myNewTable AS
SELECT cast(myIntThatIsZeroOrOne as bit) AS myBit
FROM myOldtable
然而，sql 对转换有点不满意.我如何告诉它选择一个 int 列(我知道它只有 0 和 1)?
However sql is very unhappy at casting as a bit. How can I tell it to select an int column (which I know only has 0s and 1s) as a bit?
推荐答案
你不能！
CAST 和 CONVERT 仅适用于:
CAST and CONVERT only work to:
- 二进制[(N)]
- CHAR[(N)]
- 日期
- 日期时间
- 十进制[(M[,D])]
- 签名 [整数]
- 时间
- 无符号[整数]
没有空间用于:BIT、BITINT、TINYINT、MEDIUMINT、BIGINT、SMALLINT、......
No room for: BIT, BITINT, TINYINT, MEDIUMINT, BIGINT, SMALLINT, ...
但是，您可以创建自己的函数 cast_to_bit(n):
However, you can create your own function cast_to_bit(n):
DELIMITER $$
CREATE FUNCTION cast_to_bit (N INT) RETURNS bit(1)
BEGIN
RETURN N;
END
要自己尝试，您可以创建包含多种转换的视图，例如:
To try it yourself, you can create view with several conversions like:
CREATE VIEW view_bit AS
SELECT
cast_to_bit(0),
cast_to_bit(1),
cast_to_bit(FALSE),
cast_to_bit(TRUE),
cast_to_bit(b'0'),
cast_to_bit(b'1'),
cast_to_bit(2=3),
cast_to_bit(2=2)
...然后描述它！
DESCRIBE view_bit;
呸！！现在每个人都位(1)！！！
Ta-dah!! Everyone is bit(1) now!!!
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