You want to add a unique index to a table, and unfortunately, there are already many duplicate rows in it. Manually find and delete these rows is time-wasting and error-prone. So why won't we just write one SQL statement and quickly resolve it?
First try, I wrote the following statement, and it won't work:
DELETE FROM PromotionSkus A
WHERE
A.SkuId IN (SELECT SkuId FROM PromotionSkus B GROUP BY B.SkuId HAVING COUNT(B.SkuId) > 1)
AND
A.Id NOT IN (SELECT MIN(Id) FROM PromotionSkus C GROUP BY C.SkuId HAVING COUNT(C.SkuId) > 1);
AND this one below works!
DELETE FROM PromotionSkus A
WHERE
A.Id NOT IN (SELECT Id FROM (SELECT MIN(Id) AS Id, COUNT(SkuId) AS Total FROM PromotionSkus GROUP BY SkuId HAVING Total > 1) AS B)
AND
A.SkuId IN (SELECT SkuId FROM (SELECT SkuId FROM PromotionSkus GROUP BY SkuId HAVING COUNT(SkuId) > 1) AS C);
The reason is well explained in this brilliant article.
Another mysql tip: using mysqldump export a table with one line one row.
mysqldump --databases YourDataBaseName --tables YourTableName --skip-extended-insert
Why do we need that? It is much easier to compare !
按最近提交的提交时间（DESC）列出本地分支
git branch --sort=-committerdate
太长记不住？运行下面的命令配置一个git命令别名，下次只需要敲 git brs 即可得到同样结果：
git config --global alias.brs "branch --sort=-committerdate"
解决git 命令行把中文文件名显示成 \343\200\212类似乱码的问题
git config --global core.quotepath off
将变更加入缓冲区，但不加入空白（空格、制表符或者换行符）的变更
git diff -w | git apply --cached --ignore-whitespace
Reference
git diff 时排除掉某些不想看的文件
git diff -- . ':(exclude)db/irrelevant.php' ':(exclude)db/irrelevant2.php'
删除远端分支
git push origin --delete branchname
嫌打字麻烦的，可以使用以下简写命令
git push origin :branchname
发现文件丢了不知道谁删的，比如 yarn.lock , 用下面这个命令
git log -p -- yarn.lock
设置总是push到远端的同名分支，从此再也不用如此麻烦的敲 git push -u origin theSameBranchName，你只管 git push 就好！
git config --global push.default current
解决 git diff 时出现讨厌的 ^M
git config --global core.whitespace cr-at-eol
Reference
更多的技巧请访问我的 GotGit 群组
最近一直在写 .net core，它有诸多优点我且不提，我实在头痛于手写注入服务时的模式化代码，因此动了心思要写个小脚本帮我自动化一些事情。我的想法是告诉我要加入的 ServiceName， 指定一个 Controller然后脚本自动在这个 Controller 里声明一个 private readonly 属性，自动修改类的construction 函数，自动注入这个服务，并在construction 函数体写上 _serviceName = serviceName;
在第一步，注入 private readonly 属性那里，我就绊了个跟头。用 sed 匹配到某行，在它之前，或者之后插入数据是简单的。但我匹配到 public class xxxController 这行之后是单独一行 {，而我要加的变量要放到 {这行之后。网上一通搜索，试图找到定位到某行之后N行的命令，然而并没有这样的命令。然而功夫不负有心人，我最后还是找到了一个解决方案，那就是
sed '/pattern/!b;n;n;i\something'
具体解释见
Reference
其实很简单，但因为网上有流传很广的教程并不适用于最新的 ubuntu 20.04，造成我也走了一点弯路。
certbot-auto 官方已停止维护，但网上广为流传的教程仍然推荐使用 certbot-auto 来生成证书。这是问题的根源。正确的姿势是这样的
sudo apt install certbot
sudo certbot certonly --manual -d *.yourdomain.com -d youdomain.com --preferred-challenges dns-01 --server https://acme-v02.api.letsencrypt.org/directory
照提示一步一步来就好了。是不是超级简单？
I originally thought the later should be used. I was wrong.