mysql中generated always as的使用

-- generated always as的使用
CREATE TABLE t1(
c1 INT,
c2 DOUBLE(20,19) ,
c3 INT GENERATED ALWAYS AS(c1*2));
SELECT *FROM t1;
INSERT INTO t1(c1,c2) VALUE(2,RAND()*10);
DROP TABLE t1;

concat在mysql中是连接

SELECT CONCAT('a','6','cc');

SELECT IF('男'='男','先生','女士') gender;

-- mid('',2,3)从第2位开始截取，截取3个
SELECT MID('java',2,2);
SET @id='41152119990816461X';
-- select mid('41152119990816461X',7,8);
SELECT DATE_FORMAT(STR_TO_DATE(MID(@id,7,8),'%Y%m%d'),'%Y年%m月%d日');-- 出生日期;
SELECT STR_TO_DATE(MID(@id,7,8),'%Y%n%d'),CURDATE();