chan uniq art 索引 nal ext 必須 length 如果

mysl事務（innodb支持事務處理） 在Mysql控制臺使用事務來操作 mysql> begin； ＃開始一個事務 mysql> insert into a (a) values(555); mysql>rollback; 回滾 ， 這樣數據是不會寫入的 當然如果上面的數據沒問題，就輸入commit提交命令就行； mysql> use oldboydb Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> begin; （開啟事務） Query OK, 0 rows affected (0.00 sec) mysql> select * from student; +----+----------+---------------+------+ | id | name | register_date | sex | +----+----------+---------------+------+ | 1 | ZhanYang | 2018-06-20 | NULL | | 4 | LiuJia | 2018-05-30 | NULL | | 8 | JiaLiu | 2018-06-20 | NULL | | 9 | JiaLiu | 2018-04-20 | NULL | | 10 | gaoyf | 2018-04-20 | NULL | | 11 | zhujh | 2018-04-20 | NULL | | 12 | zhouha | 2018-04-20 | NULL | | 13 | hanzb | 2018-04-21 | M | +----+----------+---------------+------+ 8 rows in set (0.00 sec) mysql> insert into student (name,register_date,sex) values("Alex","2016-05-21","M"); Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into student (name,register_date,sex) values("Jack","2016-05-21","M"); Query OK, 1 row affected (0.00 sec) mysql> select * from student; +----+----------+---------------+------+ | id | name | register_date | sex | +----+----------+---------------+------+ | 1 | ZhanYang | 2018-06-20 | NULL | | 4 | LiuJia | 2018-05-30 | NULL | | 8 | JiaLiu | 2018-06-20 | NULL | | 9 | JiaLiu | 2018-04-20 | NULL | | 10 | gaoyf | 2018-04-20 | NULL | | 11 | zhujh | 2018-04-20 | NULL | | 12 | zhouha | 2018-04-20 | NULL | | 13 | hanzb | 2018-04-21 | M | | 14 | Alex | 2016-05-21 | M | | 15 | Jack | 2016-05-21 | M | +----+----------+---------------+------+ 10 rows in set (0.00 sec) mysql> rollback; （回滾） Query OK, 0 rows affected (0.00 sec) mysql> select * from student; +----+----------+---------------+------+ | id | name | register_date | sex | +----+----------+---------------+------+ | 1 | ZhanYang | 2018-06-20 | NULL | | 4 | LiuJia | 2018-05-30 | NULL | | 8 | JiaLiu | 2018-06-20 | NULL | | 9 | JiaLiu | 2018-04-20 | NULL | | 10 | gaoyf | 2018-04-20 | NULL | | 11 | zhujh | 2018-04-20 | NULL | | 12 | zhouha | 2018-04-20 | NULL | | 13 | hanzb | 2018-04-21 | M | +----+----------+---------------+------+ 8 rows in set (0.00 sec) mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> insert into student (name,register_date,sex) values("ZhanXing","2018-05-21","M"); Query OK, 1 row affected (0.00 sec) mysql> insert into student (name,register_date,sex) values("XingYan","2018-05-21","M"); Query OK, 1 row affected (0.00 sec) mysql> select * from student; +----+----------+---------------+------+ | id | name | register_date | sex | +----+----------+---------------+------+ | 1 | ZhanYang | 2018-06-20 | NULL | | 4 | LiuJia | 2018-05-30 | NULL | | 8 | JiaLiu | 2018-06-20 | NULL | | 9 | JiaLiu | 2018-04-20 | NULL | | 10 | gaoyf | 2018-04-20 | NULL | | 11 | zhujh | 2018-04-20 | NULL | | 12 | zhouha | 2018-04-20 | NULL | | 13 | hanzb | 2018-04-21 | M | | 16 | ZhanXing | 2018-05-21 | M | | 17 | XingYan | 2018-05-21 | M | +----+----------+---------------+------+ 10 rows in set (0.00 sec) mysql> commit; （從內存寫入磁盤） Query OK, 0 rows affected (0.00 sec) mysql> select * from student; +----+----------+---------------+------+ | id | name | register_date | sex | +----+----------+---------------+------+ | 1 | ZhanYang | 2018-06-20 | NULL | | 4 | LiuJia | 2018-05-30 | NULL | | 8 | JiaLiu | 2018-06-20 | NULL | | 9 | JiaLiu | 2018-04-20 | NULL | | 10 | gaoyf | 2018-04-20 | NULL | | 11 | zhujh | 2018-04-20 | NULL | | 12 | zhouha | 2018-04-20 | NULL | | 13 | hanzb | 2018-04-21 | M | | 16 | ZhanXing | 2018-05-21 | M | | 17 | XingYan | 2018-05-21 | M | +----+----------+---------------+------+ 10 rows in set (0.00 sec) MySQL索引： 創建索引 這是最基本的索引，它沒有任何限制。它有以下幾種創建方式： CREATE INDEX indexName ON mytable(username(length)); 如果是CHAR，VARCHAR類型，length可以小於字段實際長度；如果是BLOB和TEXT類型，必須指定 length。 修改表結構 ALTER mytable ADD INDEX [indexName] ON (username(length)) 創建表的時候直接指定 CREATE TABLE mytable( ID INT NOT NULL, username VARCHAR(16) NOT NULL, INDEX [indexName] (username(length)) ); 刪除索引的語法 DROP INDEX [indexName] ON mytable; mysql> mysql> show index from student; （查看索引） +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | student | 0 | PRIMARY | 1 | id | A | 10 | NULL | NULL | | BTREE | | | +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 1 row in set (0.00 sec) mysql> create index index_name on student (name(32)); （創建索引） Query OK, 0 rows affected (0.05 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show index from student; +---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | student | 0 | PRIMARY | 1 | id | A | 10 | NULL | NULL | | BTREE | | | | student | 1 | index_name | 1 | name | A | 10 | NULL | NULL | | BTREE | | | +---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 2 rows in set (0.00 sec) mysql> drop index index_name on student; （刪除索引） Query OK, 0 rows affected (0.04 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show index from student; +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | student | 0 | PRIMARY | 1 | id | A | 10 | NULL | NULL | | BTREE | | | +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 1 row in set (0.00 sec) 唯一索引： 它與前面的普通索引類似，不同的就是：索引列的值必須唯一，但允許有空值。 如果是組合索引，則列值的組合必須唯一。它有以下幾種創建方式： 創建索引 CREATE UNIQUE INDEX indexName ON mytable(username(length)) 修改表結構 ALTER mytable ADD UNIQUE [indexName] ON (username(length)) 創建表的時候直接指定 CREATE TABLE mytable( ID INT NOT NULL, username VARCHAR(16) NOT NULL, UNIQUE [indexName] (username(length)) ); 使用ALTER 命令添加和刪除索引 有四種方式來添加數據表的索引： ALTER TABLE tbl_name ADD PRIMARY KEY (column_list): 該語句添加一個主鍵，這意味著索引值必須是唯一的，且不能為NULL。 ALTER TABLE tbl_name ADD UNIQUE index_name (column_list): 這條語句創建索引的值必須是唯一的（除了NULL外，NULL可能會出現多次）。 ALTER TABLE tbl_name ADD INDEX index_name (column_list): 添加普通索引，索引值可出現多次。 ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list):該語句指定了索引為 FULLTEXT ，用於全文索引。 以下實例為在表中添加索引。 mysql> ALTER TABLE testalter_tbl ADD INDEX (c); 你還可以在 ALTER 命令中使用 DROP 子句來刪除索引。嘗試以下實例刪除索引: mysql> ALTER TABLE testalter_tbl DROP INDEX (c);

mysql事務、索引