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法學如果我截斷一張表，還應該新增索引嗎？
如果你截斷了一張表，則不需要新增索引，因為表在被截斷後會重新建立，索引也會自動新增。
我們首先建立一個表：-
mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> FirstName varchar(20), -> LastName varchar(20) -> ); Query OK, 0 rows affected (0.65 sec)
以下查詢用來建立索引：-
mysql> create index Index_firstName_LastName on DemoTable(FirstName,LastName); Query OK, 0 rows affected (1.04 sec) Records: 0 Duplicates: 0 Warnings: 0
使用插入命令在表中插入一些記錄：-
mysql> insert into DemoTable(FirstName,LastName) values('John','Smith');
Query OK, 1 row affected (0.47 sec使用 select 語句顯示錶中的所有記錄：-
mysql> select *from DemoTable;
輸出
這將產生以下輸出：-
+----+-----------+----------+ | Id | FirstName | LastName | +----+-----------+----------+ | 1 | John | Smith | +----+-----------+----------+ 1 row in set (0.00 sec)
在截斷表之前，你需要檢查表的 status：-
mysql> show create table DemoTable;
輸出
這將產生以下輸出：-
+--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table| +--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | DemoTable | CREATE TABLE `DemoTable` (`Id` int(11) NOT NULL AUTO_INCREMENT,`FirstName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL,`LastName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL,PRIMARY KEY (`Id`),KEY `Index_firstName_LastName` (`FirstName`,`LastName`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci | +--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
現在截斷表：-
mysql> truncate table DemoTable; Query OK, 0 rows affected (2.01 sec)
現在再次檢查表的狀態。你不需要新增索引：-
mysql> show create table DemoTable;
輸出
這將產生以下輸出：-
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | DemoTable | CREATE TABLE `DemoTable` (`Id` int(11) NOT NULL AUTO_INCREMENT,`FirstName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL,`LastName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL, PRIMARY KEY (`Id`),KEY `Index_firstName_LastName` (`FirstName`,`LastName`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci | +--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
更新於： 2020 年 6 月 30 日
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