mysql中不能創建索引的語句？

一、創建索引

1.PRIMARY KEY（主鍵索引）

mysql > ALTER TABLE `table_name` ADD PRIMARY KEY ( `column` )

2.UNIQUE(唯一索引)

mysql > ALTER TABLE `table_name` ADD UNIQUE (`column` )

3.INDEX(普通索引)

mysql > ALTER TABLE `table_name` ADD INDEX index_name ( `column` )

4.FULLTEXT(全文索引)

mysql > ALTER TABLE `table_name` ADD FULLTEXT ( `column` )

5.多列索引(組合索引)

mysql > ALTER TABLE `table_name` ADD INDEX index_name ( `column1`, `column2`, `column3` )

CREATE TABLE table_name ( ID INT NOT NULL, username VARCHAR(16) NOT NULL, city VARCHAR(50) NOTNULL, age INT NOT NULL );