如何在MySql SELECT语句中正确使用CAST函数？ [英] How to use the CAST function correctly in a MySql SELECT statement?

问题描述

我正在将一个MSSQL数据库转换为MySQL数据库，我有一个存储过程，使用cast函数从datetime数据类型转换为varchar数据类型。是否这在php / mysql中是重要的，因为php不是强类型的（我不知道是否重要）我真的想保持SP尽可能接近原始的，所以我可以保持相同的预期功能。问题是，我不能得到cast函数在mysql中正常工作。这是一个测试我试过，给我一个错误：

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:

DELIMITER ;//

DROP PROCEDURE IF EXISTS `test`;//
CREATE PROCEDURE `test`()
BEGIN
  SELECT CAST(my_table.DateColumn AS VARCHAR(10)) as TextColumn
    FROM my_table;
END;//

我做错了什么？

推荐答案

VARCHAR不是CAST函数的有效类型，但CHAR为。

VARCHAR isn't a valid type for the CAST function, but CHAR is.

SELECT CAST(my_table.DateColumn AS CHAR(10)) as TextColumn FROM my_table;

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