[英]In mysql, how do I select ONLY every row that has the same value in one column but different ones in another?
[英]In MySQL, how do you automatically set a value for one column when updating another in the same row?
對於下面的示例表,是否可以將表配置為在發生UPDATE時使用“值”列中的數據自動更新PreviousValue列?
table Settings
(
Setting varchar(255),
Value varchar(255),
PreviousValue varchar(255)
)
CREATE TRIGGER my_trigger BEFORE UPDATE ON my_table FOR EACH ROW
SET NEW.PreviousValue = OLD.Value;
沒有觸發器,您也可以通過以下方法實現此目的:
UPDATE Settings SET PreviousValue = Value, Value = :new_value WHERE Setting = :setting
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