随机应变 ABCD: Always Be Coding and … : хороший
[ccs]
#qa dt .q {
padding:2px 5px 2px 5px;
background-color:orangered;
color:#fff;
margin-right:5px;
}
#qa dd .a {
padding:2px 5px 2px 5px;
background-color:orangered;
color:#fff;
margin-right:5px;
}
[/ccs]
邪道かな。やっぱimgでやるべきか。。
Originally, if either is a primary aircraft, the other must be a secondary aircraft, but both are primary aircraft.
In this way, a situation where multiple primary machine exist when a cluster is split is called split brain. If data is updated in this state, data inconsistencies may occur.
Why does split brain occur?
-> Split brain is mainly caused by network failure between the first and second units.
>KEY は通常、INDEX のシノニムです。キー属性 PRIMARY KEY もまた、カラム定義内で指定する場合は、単に KEY として指定できます。これは、ほかのデータベースシステムとの互換性のために実装されました。
Indexって理解でOK?
->確実に 識別する(identification) ための 主たる制約
Integer types can handle positive and negative numbers, but if the data type is followed by UNSIGNED, only 0 and positive numbers can be stored. Such data types are called unsigned integer types. For example, to make INT type unsigned, write as follows.
mysql> create table numtest(
-> num1 smallint unsigned
-> );
Query OK, 0 rows affected (0.17 sec)
mysql> insert into numtest values(5000);
Query OK, 1 row affected (0.12 sec)
mysql> insert into numtest values(-10);
Query OK, 1 row affected, 1 warning (0.03 sec)
mysql> select * from numtest;
+——+
| num1 |
+——+
| 5000 |
| 0 |
+——+
2 rows in set (0.00 sec)
CREATE TABLEの際にcommentを追加する
mysql> CREATE TABLE corporate(
-> name varchar(255) comment ‘商号’,
-> address varchar(255) comment ‘所在地’
-> )
-> default charset=utf8
-> comment=’会社テーブル’;
Query OK, 0 rows affected (0.36 sec)
mysql> describe corporate;
+———+————–+——+—–+———+——-+
| Field | Type | Null | Key | Default | Extra |
+———+————–+——+—–+———+——-+
| name | varchar(255) | YES | | NULL | |
| address | varchar(255) | YES | | NULL | |
+———+————–+——+—–+———+——-+
2 rows in set (0.06 sec)
show full columnsでカラムのcomment表示
mysql> show full columns from corporate;
+———+————–+—————–+——+—–+———+——-+—– —————————-+———–+
| Field | Type | Collation | Null | Key | Default | Extra | Priv ileges | Comment |
+———+————–+—————–+——+—–+———+——-+—– —————————-+———–+
| name | varchar(255) | utf8_general_ci | YES | | NULL | | sele ct,insert,update,references | 商号 |
| address | varchar(255) | utf8_general_ci | YES | | NULL | | sele ct,insert,update,references | 所在地 |
+———+————–+—————–+——+—–+———+——-+—– —————————-+———–+
2 rows in set (0.00 sec)
カラムの要件定義でカラムの意味は決めるので、sqlの中にわざわざcommentを追加する必要性は限られるようにも思うが、ケースバイケースということか？
– どのユーザーがいるか知りたい
SELECT user, host, password FROM mysql.user
mysql> select user,host from mysql.user;
+——+———————–+
| user | host |
+——+———————–+
| user | % |
| root | 127.0.0.1 |
| root | ::1 |
| | localhost |
| root | localhost |
| saru | localhost |
| | localhost.localdomain |
| root | localhost.localdomain |
+——+———————–+
8 rows in set (0.21 sec)
-ユーザー権限
SHOW GRANTS FOR root@`localhost`
mysql> show grants for root@localhost;
+———————————————————————+
| Grants for root@localhost |
+———————————————————————+
| GRANT ALL PRIVILEGES ON *.* TO ‘root’@’localhost’ WITH GRANT OPTION |
| GRANT PROXY ON ”@” TO ‘root’@’localhost’ WITH GRANT OPTION |
+———————————————————————+
2 rows in set (0.06 sec)
– 管理用ユーザー
GRANT ALL ON *.* TO adminuser@`%` IDENTIFIED BY ‘password’ WITH GRANT OPTION;
– IP制限
GRANT ALL ON *.* TO adminuser@’172.16.0.0/255.255.255.0′ IDENTIFIED BY ‘password’ WITH GRANT OPTION;
– 全てのデータベースにアクセス
GRANT ALL ON *.* TO testuser@’%’ IDENTIFIED By ‘password’;
– 特定のデータベースにアクセス
GRANT ALL ON testdatabase.* TO testuser@’%’ IDENTIFIED BY ‘password’;
ref: create user with GRANT Privileges in Terminal
cat /proc/version
[vagrant@localhost ~]$ cat /proc/version
Linux version 2.6.32-754.14.2.el6.x86_64 (mockbuild@x86-01.bsys.centos.org) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-23) (GCC) ) #1 SMP Tue May 14 19:35:42 UTC 2019
uname -a
[vagrant@localhost ~]$ uname -a
Linux localhost.localdomain 2.6.32-754.14.2.el6.x86_64 #1 SMP Tue May 14 19:35:42 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
unameだと、usernameが出てきますね。
cat /etc/system-release
[vagrant@localhost ~]$ cat /etc/system-release
CentOS release 6.10 (Final)
これが一般的か。
ちなみに、最新のLinuxはというと、、、
カーネルは4.18.0-80が最新のようですね。
There are two types of character code, Unicode, which has no BOM and with a BOM. BOM stands for byte order mark, which is a few bytes of data attached to the beginning of Unicode encoded text.
When the program reads text data, it determines from the first few bytes that it is Unicode data and which kind of encoding format is adopted. In the case of UTF-8 with BOM, the first 3 bytes are BOM, and the data is <0xEF 0xBB 0xBF>
Depending on the application such as Microsoft Excel, it may not be possible to determine whether the encoding method is UTF-8, UTF-16, UTF-32, or another different character code unless BOM is added. On the other hand, for HTML files used as web pages, it is better to save / overwrite without BOM. This is because some programs such as PHP that process web pages dynamically can not process text files with BOMs correctly. It can not generally be said that which way is better depending on the situation like this.
The difference between a file with BOM and a file without BOM is the presence or absence of the first 3 bytes, and the contents of other files and the character code (encoding system) are exactly the same. This means that if the encoding method is not correct, it will be displayed normally as a simple text file, so it can be said that it is difficult to notice that the BOM is the cause if the file malfunctions in any program.
ref:
<html>
<head>
<title>二重送信を防ぐ</title>
<style>
.btn-wrap {
width: 300px;
margin: 0 auto;
text-align: center;
}
.loading {
display:none;
}
</style>
</head>
<body>
<div class="btn-wrap">
<button class="btn">送信</button>
<div class="loading">
<img src="loading.gif">
</div>
</div>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script>
$(function(){
$('.btn').on('click', function(){
$('.btn').hide();
$('.loading').show();
});
});
</script>
</body>
</html>
<html>
<head>
<title>二重送信を防ぐ</title>
<script>
var flag = false;
function send(){
if(flag){
alert("送信済みです");
return false;
flag = true;
}
}
</script>
</head>
<body>
<a href="javascript:send()">データを送信</a>
</body>
</html>
あれ、上手くいかない。。
書き方を変えます。
<html>
<head>
<title>二重送信を防ぐ</title>
<script>
var set=0:
function double(){
if(set==0){
set=1;
} else{
alert("只今処理中です。\nそのままおまちください");
return false;
}
}
</script>
</head>
<body>
<form action="" method="post">
<input type="submit" name="go" class="test" value="送信" onClick="javascript:double(this)">
</form>
</body>
</html>
うーんちょっと違うようです。
<body>
<form action="" method="post">
<input type="submit" name="go" id="login_submit" class="" value="送信">
</form>
<script
src="https://code.jquery.com/jquery-3.4.1.min.js"
integrity="sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo="
crossorigin="anonymous"></script>
<script>
$('#login_a').on('click', function(){
if($(this).hasClass('double_click')){
return false;
}
$(this).text("送信中...");
$(this).addClass('double_click');
});
</script>
</body>
あれーーーーーーーーー