mysql 从另一列中选择列值

Question

I have a mysql query

select host, domain from table

Output:
host                        domain
host1.abc.com               abc.com 
host2.abc.com               null

I want to change the query so that I get domain value from the first column by stripping out the host part. I don't want to query the domain value from the table because some of it is blank

This way domain for host - host2.abc.com would be abc.com

Answer 1

DROP TABLE bleach;

CREATE TABLE bleach (`host` VARCHAR(50) NOT NULL);

INSERT INTO bleach (`host`) VALUES ('host1.abc.com');
INSERT INTO bleach (`host`) VALUES ('host29.abcdefg.com');

SELECT * FROM bleach;

SELECT `host`, SUBSTRING_INDEX(`host`,'.',-2) FROM bleach;

OUTPUT:

host                 SUBSTRING_INDEX(`host`,'.',-2)
host1.abc.com        abc.com
host29.abcdefg.com   abcdefg.com