MySQL federated primary key_ MySQL creates a federated primary key [easy to understand]

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Mysql Create a federated primary key

2008 year 01 month 11 Japan Friday Afternoon 5:21

Use primary key (fieldlist)

such as ：

create table mytable (

aa int,

bb char(8),

cc date,

primary key (aa,bb )

);

aa,bb For union primary key

I don't know if it's because mysql(6.0) Version issue for , Or is this the case in all versions ,mysql Create a federated primary key , The joint primary key column name cannot be enclosed in single quotation marks , Otherwise there will be a mistake , could not be built , The error is that the column does not exist in the table . The example code is as follows ：

CREATE TABLE `book_sort2` (

`sort_id2` varchar(20) NOT NULL,

`sort_id1` varchar(20) NOT NULL COMMENT ‘ A class id’,

`sort_name2` varchar(20) NOT NULL COMMENT ‘ Class II name ’,

PRIMARY KEY (sort_id2,sort_id1),

KEY `sort_id1` (`sort_id1`),

CONSTRAINT `book_sort2_fk` FOREIGN KEY (`sort_id1`) REFERENCES `book_sort1` (`sort_id1`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

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We all know that when we need to 2 When the uniqueness of the record can be determined only by the above Columns , You need a federated primary key , After establishing a federated primary key , When querying data, the performance will be greatly improved , However, the performance will not be improved when any column of the federated primary key is queried separately , But I …

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