<?xml version="1.0" encoding="utf-8" ?><rss version="2.0"><channel><title><![CDATA[weixin_48680010的博客]]></title><description><![CDATA[]]></description><link>https://blog.youkuaiyun.com/weixin_48680010</link><language>zh-cn</language><generator>https://blog.youkuaiyun.com/</generator><copyright><![CDATA[Copyright &copy; weixin_48680010]]></copyright><item><title><![CDATA[mysql日期操作]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/138086741</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/138086741</guid><author>weixin_48680010</author><pubDate>Mon, 22 Apr 2024 18:14:22 +0800</pubDate><description><![CDATA[https://blog.youkuaiyun.com/weixin_44259720/article/details/103496184]]></description><category></category></item><item><title><![CDATA[mysql多表查询时与子表的关系]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/137830703</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/137830703</guid><author>weixin_48680010</author><pubDate>Tue, 16 Apr 2024 16:38:34 +0800</pubDate><description><![CDATA[如果最后一句代码不把a与两个表都进行连接的话会出现结果重复的问题。]]></description><category></category></item><item><title><![CDATA[mysql not in 和 null]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/137796671</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/137796671</guid><author>weixin_48680010</author><pubDate>Mon, 15 Apr 2024 21:38:21 +0800</pubDate><description><![CDATA[not in语句后面的范围不能出现null，否则执行无效，如果后面是子查询，则需要手动增加is not null过滤条件。本题中如果将第二个case中的in改成not in，因为目标中有null 则会直接跳过第二个case进入else。in语句不会对null进行过滤匹配。]]></description><category></category></item><item><title><![CDATA[date_format]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/137278517</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/137278517</guid><author>weixin_48680010</author><pubDate>Tue, 02 Apr 2024 17:33:06 +0800</pubDate><description><![CDATA[DATE_FORMAT(date, format)]]></description><category></category></item><item><title><![CDATA[case if]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136920516</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136920516</guid><author>weixin_48680010</author><pubDate>Thu, 21 Mar 2024 20:55:45 +0800</pubDate><description><![CDATA[【代码】case if。]]></description><category></category></item><item><title><![CDATA[MySQL 将null值替换成0]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136887215</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136887215</guid><author>weixin_48680010</author><pubDate>Wed, 20 Mar 2024 20:03:13 +0800</pubDate><description><![CDATA[coalesce]]></description><category></category></item><item><title><![CDATA[join。]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136887192</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136887192</guid><author>weixin_48680010</author><pubDate>Wed, 20 Mar 2024 20:02:19 +0800</pubDate><description><![CDATA[力扣
四大join]]></description><category></category></item><item><title><![CDATA[正则表达式]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136879769</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136879769</guid><author>weixin_48680010</author><pubDate>Wed, 20 Mar 2024 19:58:50 +0800</pubDate><description><![CDATA[正则表达式力扣]]></description><category></category></item><item><title><![CDATA[having和where的区别]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136855223</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136855223</guid><author>weixin_48680010</author><pubDate>Tue, 19 Mar 2024 20:57:49 +0800</pubDate><description><![CDATA[having和where的区别
力扣题目链接]]></description><category></category></item><item><title><![CDATA[cuda cudnn安装]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136750304</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136750304</guid><author>weixin_48680010</author><pubDate>Fri, 15 Mar 2024 21:22:37 +0800</pubDate><description><![CDATA[注意 cudnn对应的cuda的10.0版本无win11版本 下载win10 即可。]]></description><category></category></item><item><title><![CDATA[SQL面试学习 行列转换]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136721965</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136721965</guid><author>weixin_48680010</author><pubDate>Thu, 14 Mar 2024 21:22:11 +0800</pubDate><description><![CDATA[concat_ws：把集合中的值用指定分隔符连接collect_set（）：收集唯一值并返回一个集合cast（）将任何类型的值转换为具有指定类型的值。]]></description><category></category></item><item><title><![CDATA[cast数据类型转换]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136690048</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136690048</guid><author>weixin_48680010</author><pubDate>Wed, 13 Mar 2024 20:09:04 +0800</pubDate><description><![CDATA[函数，您可以将一个值从一种数据类型转换为另一种数据类型，以便在查询中进行比较、计算或显示。数据类型，以便在结果中显示具有特定精度和小数位数的数字。函数用于将一个值转换为另一种数据类型。是要转换成的目标数据类型。将计算出的平均时间间隔转换为。]]></description><category></category></item><item><title><![CDATA[mysql重构]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136687095</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136687095</guid><author>weixin_48680010</author><pubDate>Wed, 13 Mar 2024 18:51:33 +0800</pubDate><description><![CDATA[在这个例子中，‘store1’ AS store表示将名为’store1’的列的别名设为store，store1 AS price表示将名为store1的列的别名设为price。在查询结果中，store1列将以store的名称显示，store1列将以price的名称显示。]]></description><category></category></item><item><title><![CDATA[group by order by having where union]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136602871</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136602871</guid><author>weixin_48680010</author><pubDate>Sun, 10 Mar 2024 15:38:50 +0800</pubDate><description><![CDATA[1，order by 从英文里理解就是行的排序方式，默认的为升序。order by 后面必须列出排序的字段名，可以是多个字段名。2，group by 从英文里理解就是分组。必须有“聚合函数”来配合才能使用，使用时至少需要一个分组标志字段。注意：聚合函数是—sum()、count()、avg()等都是“聚合函数”UNION 操作会对结果去重且排序。union all 不去重。]]></description><category></category></item><item><title><![CDATA[lag lead]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136572574</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136572574</guid><author>weixin_48680010</author><pubDate>Fri, 08 Mar 2024 21:30:57 +0800</pubDate><description><![CDATA[力扣题目链接lag lead用法]]></description><category></category></item><item><title><![CDATA[join sum 时间范围]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136571228</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136571228</guid><author>weixin_48680010</author><pubDate>Fri, 08 Mar 2024 20:31:27 +0800</pubDate><description><![CDATA[力扣题目链接datetime date timestamp三种类型的上下界MySQL 中 datetime 和 timestamp 的区别与选择]]></description><category></category></item><item><title><![CDATA[窗口函数dense（） over（条件）]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136546480</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136546480</guid><author>weixin_48680010</author><pubDate>Thu, 07 Mar 2024 21:23:19 +0800</pubDate><description><![CDATA[在 SQL 中，DENSE_RANK() 是一个窗口函数，用于计算结果集中每行的稠密排名（dense rank）。DENSE_RANK() 函数会为具有相同排序字段值的行分配相同的排名，但不会跳过排名。在上面的示例中，DENSE_RANK() 函数按照薪水（Salary）字段降序排列员工，并为每个员工分配一个稠密排名。请注意，DENSE_RANK() 函数在计算稠密排名时不会跳过排名，即如果有两个员工具有相同的薪水，它们将被分配相同的排名，并且下一个排名将不会跳过。]]></description><category></category></item><item><title><![CDATA[数据库自连接]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136546130</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136546130</guid><author>weixin_48680010</author><pubDate>Thu, 07 Mar 2024 21:08:10 +0800</pubDate><description><![CDATA[力扣题目链接https://leetcode.cn/problems/employees-earning-more-than-their-managers。]]></description><category></category></item><item><title><![CDATA[left join]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/136545630</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/136545630</guid><author>weixin_48680010</author><pubDate>Thu, 07 Mar 2024 20:48:03 +0800</pubDate><description><![CDATA[LEFT JOIN]]></description><category></category></item><item><title><![CDATA[二分法查找]]></title><link>https://blog.youkuaiyun.com/weixin_48680010/article/details/130590544</link><guid>https://blog.youkuaiyun.com/weixin_48680010/article/details/130590544</guid><author>weixin_48680010</author><pubDate>Tue, 09 May 2023 23:42:00 +0800</pubDate><description><![CDATA[个人认为本题是二分查找较为有难度的题，因为要求了时间复杂度（符合条件常用的有折半查找，幂查找，欧几里得），此处寻找左右边界各使用一次二分查找。此处以右边界为例，左边界同理。二分法是查找时间复杂度较低的算法之一：o（log n），实际上就是寻找low high中间位置的值，不断增大low，缩小high的值来缩小范围。实际上的改变就是else语句处，写个数组即可理解。34.在排序数组中查找元素的第一个和最后一个位置。力扣上同类型的还有35.搜索插入位置。367.有效的完全平方数等。]]></description><category></category></item></channel></rss>