mysql5.7 生成列 generated column用法实例分析

col_name data_type [GENERATED ALWAYS] AS (expression)
 [VIRTUAL | STORED] [NOT NULL | NULL]
 [UNIQUE [KEY]] [[PRIMARY] KEY]
 [COMMENT 'string']

CREATE TABLE test (
 id INT (11) UNSIGNED NOT NULL AUTO_INCREMENT,
 chinese DOUBLE NOT NULL DEFAULT '0',
 math DOUBLE NOT NULL DEFAULT '0',
 english DOUBLE NOT NULL DEFAULT '0',
 total_score DOUBLE AS (chinese + math + english),
 PRIMARY KEY (id)
) ENGINE=INNODB DEFAULT CHARSET=utf8mb4;

insert into test(chinese, math, english) values(66, 72, 54);

select  from test;

insert into test(chinese, math, english, total_score) values(33, 44, 55, DEFAULT);

alter table test add column times_score double generated always 
as (chinese  math  english) stored;

alter table test modify column times_score float generated always 
as (chinese  math  english  10) stored;

alter table test change times_score times_score_new float generated always 
as (chinese  math  english  10) stored;

alter table test drop column times_score_new;

alter table test drop column total_score;
alter table test add column total_score double generated always 
as (chinese + math + english) stored;

alter table test modify column chinese double generated always 
as (math + 1) stored;

alter table test modify column total_score double;