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How to add column if not exists on PostgreSQL?
...statement:
DO $$
BEGIN
BEGIN
ALTER TABLE <table_name> ADD COLUMN <column_name> <column_type>;
EXCEPTION
WHEN duplicate_column THEN RAISE NOTICE 'column <column_name> already exists in <table_name>.';
END;
END;
$$
...
Redis: Show database size/size for keys
...multiple databases I have in there consumes how much memory. Redis' INFO command just shows me the total size and the number of keys per database which doesn't give me much insight... So any tools/ideas that give me more information when monitoring the redis server would be appreciated.
...
MLKitTranslator 拓展：离线翻译 · App Inventor 2 中文网
...认 en）、一个输入框、一个按钮、一个标签。
when 按钮_翻译.Click() {
标签1.Text = "翻译中…"
MLKitTranslator1.Translate(文本输入框_输入.Text)
}
when MLKitTranslator1.GotTranslation(originalText, translatedText) {
标签1.Text = translatedText
}
when MLKitTran...
导航条使用指导 · App Inventor 2 中文网
...宽度充满父级）；
拖一个标签到屏幕上方（改名 标签_标题，用来看选中结果）；
搭下面的代码块：
when Screen1.Initialize() {
导航条1.SetItems(list("", "", "", ""), list("首页", "分类", "购物车", "我的"))
}
when 导航条1.ItemSelected(索引)...
扫码寻宝 · App Inventor 2 中文网
...。
procedure 显示线索() {
if 关卡 > length(线索) {
标签_关卡.Text = "全部通关！"
标签_线索.Text = "恭喜你找到了所有宝藏！"
} else {
标签_关卡.Text = join("第 ", 关卡, " 关 / 共 ", length(线索), " 关")
标签_线索.Text = select(线...
Is there a naming convention for MySQL?
...
MySQL has a short description of their more or less strict rules:
https://dev.mysql.com/doc/internals/en/coding-style.html
Most common codingstyle for MySQL by Simon Holywell:
http://www.sqlstyle.guide/
See also this question:
Are there any published coding style guidelines for SQL?
...
Check if two unordered lists are equal [duplicate]
...of (hashable) things, called a set. If you convert both lists to sets, the comparison will be unordered.
set(x) == set(y)
Documentation on set
EDIT: @mdwhatcott points out that you want to check for duplicates. set ignores these, so you need a similar data structure that also keeps track of th...
GestureDetector 手势检测拓展：旋转、缩放和滑动手势检测，自定义手势识别...
...。
when Screen1.Initialize() {
SwipeDetector1.AddHandler(垂直布局_手势区)
}
when SwipeDetector1.SwipeLeft() {
标签_提示.Text = "向左滑：下一页"
}
when SwipeDetector1.SwipeRight() {
标签_提示.Text = "向右滑：上一页"
}
when SwipeDetector1.DoubleClick() {
标...
How does “cat
...
This is called heredoc format to provide a string into stdin. See https://en.wikipedia.org/wiki/Here_document#Unix_shells for more details.
From man bash:
Here Documents
This type of redirection instructs the shell to read input from
the current source until a line
containin...
How to check 'undefined' value in jQuery
... variable or other unevaluated operand. The main advantage of this method, compared to if (value === undefined) { ... }, is that typeof will never raise an exception in case if variable value does not exist.
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