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<>1 概述
MySQL数据类型转换 被动转换 加号运算符 字符串连接函数 1+'1' -- 2 concat(1,'1') -- 11 主动转换 convert函数转换
cast函数转换 日期时间互转函数 convert(expr, type) cast(expr as type) str_to_date date_format
<>2 类型转换
char date、time、datetime date_format() signed、unsigned、decimal(n,m) 数值 字符 日期
select -- 数值 -> 字符 -- char(n) n 个长度的字符，超过截取 convert(2022, char(3)) c1, -- 202
convert(2022, char(4)) c2, -- 2022 convert(2022, char(5)) c3, -- 2022 -- 字符 ->
数值 convert('-12.56', SIGNED) s1, -- -12 有符号整数 convert('12.56', UNSIGNED) u1, --
12 无符号整数 convert('12.56', decimal(3, 1)) dc1, -- 12.6 浮点数，四舍五入 -- 字符 -> 日期
convert('2021-05-20 13:14:00', datetime) d1, -- 日期+时间 convert('2021-05-20
13:14:00', date) d2, -- 仅日期 convert('2021-05-20 13:14:00', time) d3, -- 仅时间
str_to_date('2021-05-20 13:14:00', '%Y-%m-%d %H:%i:%S') d4, str_to_date(now(),
'%Y-%m-%d') d5, -- 日期截取 -- 日期 -> 字符 convert(now(), char) c4, date_format(now(),
'%Y-%m-%d %H:%i:%S') c5 -- 注意大小写 from dual;
