如何在 MySql SELECT 语句中正确使用 CAST 函数？
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How to use the CAST function correctly in a MySql SELECT statement?
提问by aarona
I'm converting an MSSQL DB to MySQL DB and I have a stored procedure that is using a cast function to convert from a datetime datatype to a varchar datatype. Whether or not this matters in php/mysql since php isn't strongly typed (and I dont know if it would matter or not) I really want to keep the SP a close to the orginal as possible so I can maintain the same expected functionality. The problem is that I can't get the cast function to work right in mysql. Here is a test I tried that got me an error:
我正在将 MSSQL DB 转换为 MySQL DB，并且我有一个使用强制转换函数将日期时间数据类型转换为 varchar 数据类型的存储过程。这在 php/mysql 中是否重要，因为 php 不是强类型的（我不知道这是否重要）我真的想让 SP 尽可能接近原始版本，以便我可以保持相同的预期功能. 问题是我无法让 cast 函数在 mysql 中正常工作。这是我尝试过的测试，但出现错误：
DELIMITER ;//
DROP PROCEDURE IF EXISTS `test`;//
CREATE PROCEDURE `test`()
BEGIN
SELECT CAST(my_table.DateColumn AS VARCHAR(10)) as TextColumn
FROM my_table;
END;//
What am I doing wrong?
我究竟做错了什么？
回答by great_llama
VARCHAR isn't a valid type for the CAST function, but CHAR is.
VARCHAR 不是 CAST 函数的有效类型，但 CHAR 是.
SELECT CAST(my_table.DateColumn AS CHAR(10)) as TextColumn FROM my_table;
