Mysql method to change primary key attributes: 1. Use the keyword modify, the code is [alter table tbl_name modify....]; 2. Use the keyword change, the code is [alter table tbl_name change.. 】.
The operating environment of this tutorial: Windows 7 system, mysql version 8.0.22. This method is suitable for all brands of computers.
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Mysql method of changing primary key attributes:
1. Add primary key constraints:
alter table tbl_name add primary key (index_col_name,…); #括号中为字段名，可以为一个或者多个
2. If the data table already exists and there is no primary key, add a new field as the primary key and move the field to the table First column
alter table tbl_name add col_name col_definition (data type, null, default...) primary key first current_first_col_name; # current_first_col_name表示当前数据表的第一列
Notes: The keyword first means it is located in front of a certain column. If the added field needs to be located after a certain column, you can use after
3. The data table already exists, and There is a primary key, modify the definition of the primary key
Keyword modify
alter table tbl_name modify col_name col_definition [first|after col_name] #在col_definition 声明要修改的属性，如要添加自动编号auto_increment
Notes:
1) At this time, there is no need to re-declare the primary key attribute primary key. If it is added, an error will be reported. : Duplicate primary key;
2) If auto_increment exists in the original attribute, auto_increment needs to be added when modifying, otherwise the auto_increment attribute will be deleted
Keywordchange
alter table tbl_name change col_name col_name col_definition [first|after col_name] #与modify的区别在于列表需要写两次列名，相当于原列名和新列名，所以change也可以用来修改列名
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