创建列：
ALTER TABLE yourtable ADD COLUMN combined VARCHAR(50);
更新当前值：
UPDATE yourtable SET combined = CONCAT(zipcode, ' - ', city, ', ', state);
自动更新所有未来值：
CREATE TRIGGER insert_trigger
BEFORE INSERT ON yourtable
FOR EACH ROW
SET new.combined = CONCAT(new.zipcode, ' - ', new.city, ', ', new.state);
CREATE TRIGGER update_trigger
BEFORE UPDATE ON yourtable
FOR EACH ROW
SET new.combined = CONCAT(new.zipcode, ' - ', new.city, ', ', new.state);
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