虎搞瞎搞

I don’t remember how many times I was asked about an equivalent term of the infamous “NOLOCK” hint for mysql database server, hence I thought it was worth to write about it here. “WITH (NOLOCK)” is a transaction isolation levels that defines how data is available during an update, or with other words it is a property that defines at what point changes made by an update operation will become available in a row, table or database to other processes.

The official SQL standard defines four isolation levels:

READ COMMITTED
READ UNCOMMITTED
REPEATABLE READ
SERIALIZABLE

When WITH (NOLOCK) is used with SQL Server, the statement does not place a lock nor honor exclusive locks on table. The MySQL equivalent is READ UNCOMMITTED, also known as “dirty read” because it is the lowest level of isolation. If we specify a table hint then it will override the current default isolation level. MySQL default isolation level is REPEATABLE READ which means locks will be placed for each operation, but multiple connections can read data concurrently.

If you're getting...

"HTTP Error 404.17 - Not Found - The requested content appears to be script and will not be served by the static file handler."

...on Vista while trying to get PHP working under IIS7 with the standard ISAPI "php5isapi.dll" ask yourself, are you running 64-bit? That ISAPI DLL is a 32-bit DLL, so you'll have to either change your default Application Pool to enable 32-bit, or preferably create a separate 32-bit AppPool for your PHP Application.

Right click on the Application Pool and select "Advanced Settings" then "Enable 32-bit Applications."

net start mysql
啟動 MySQL

查詢資料庫、資料表、欄位等資訊
mysqlshow [-h ipAddress] -u user_name -p
mysqlshow -u user_name@ipAddress -p
列出所有資料庫

mysqlshow -u user_name -p db_name
列出該 database_name 所有資料表

mysqlshow -u user_name -p db_name table_name
列出該 database_name 裡 table_name 資料表裡的欄位

mysqlshow -u user_name -p db_name table_name field_name
列出該 database_name 裡 table_name 的 field_name 的欄位資訊

更改密碼
mysqladmin password 'new_password'
更改目前系統登入使用者的密碼

於資料庫中導入執行sql script 檔
mysql db_name < sql_filename.sql

與 MySQL 連線
mysql [-h ipAddress] -u user_name -ppassword
mysql [-h ipAddress] -u user_name -p

切換使用資料庫 database_name
mysql> USE db_name

mysql> SELECT DATABASE();
列出目前預設的資料庫名稱

mysql> SHOW DATABASES;
列出所有資料庫

mysql> SHOW DATABASES LIKE 'my%';
列出所有資料庫名稱為 my 開頭的

mysql> SHOW TABLES FROM db_name [LIKE ...];
列出該資料庫所有資料表名稱

mysql> SHOW COLUMNS FROM table_name [LIKE ...];
mysql> SHOW COLUMNS FROM table_name FROM db_name  [LIKE ...];
mysql> SHOW FIELDS FROM table_name [LIKE ...];
mysql> DESCRIBE table_name ;
mysql> EXPLAIN table_name ;
列出該資料表所有欄位名稱

mysql> SHOW INDEX FROM table_name [LIKE ...];
mysql> SHOW INDEX FROM table_name FROM db_name  [LIKE ...];
mysql> SHOW KEY FROM table_name [LIKE ...];
列出該資料表所有索引資訊

mysql> SHOW TABLE STATUS;
mysql> SHOW TABLE STATUS FROM db_name  [LIKE ...];列出資料表的相關資訊

mysql> SHOW VARIABLES [LIKE ...];
顯示 MySQL 相關參數設定

mysql> SHOW VARIABLES LIKE '%character%' ;
顯示資料庫語系設定資訊

mysql> SHOW PROCESSLIST;
列出與 MySQL 連線的 threads 狀態

mysql> SHOW STATUS;
列出與 MySQL 目前的狀態

當進行資料表檢查或修補時，鎖定資料表可確保資料表的安全
(READ：唯讀狀態、WRITE：無法寫入也無法讀取)
mysql> LOCK TABLE table_name READ;
mysql> FLUSH TABLES;
鎖定資料表 

mysql> UNLOCK TABLE;
資料表解除鎖定 

正則表達式（regex)是定義復雜查詢的一個強有力的工具。 
這裡是一個簡單的資料，它忽略了一些詳細的信息。 
正則表達式定義了一個字符串的規則。最簡單的正則表達式不包含任何保留字。例如， 

正則表達式hello只和字符串“hello”匹配。 

一、什麼是索引？

索引用來快速地尋找那些具有特定值的記錄，所有MySQL索引都以B-樹的形式保存。如果沒有索引，執行查詢時MySQL必須從第一個記錄開始掃瞄整個表 的所有記錄，直至找到符合要求的記錄。表裡面的記錄數量越多，這個操作的代價就越高。如果作為搜索條件的列上已經創建了索引，MySQL無需掃瞄任何記錄 即可迅速得到目標記錄所在的位置。如果表有1000個記錄，通過索引查找記錄至少要比順序掃瞄記錄快100倍。