Mysql：将某些列从一行复制到另一行

Question

Is there an easy way to as an example copy COL2 and COL3 from row with ID3 to row with ID2 and replace any existing value?

ID---COL1---COL2---COL3
1.   A        B        C
2.   D        E        F
3.   G        H        I
4.   J        K        L

Answer 1

Use UPDATE with a self-join.

UPDATE yourTable AS t1
CROSS JOIN yourTable AS t2
SET t1.col2 = t2.col2, t1.col3 = t2.col3
WHERE t1.id = 2
AND t2.id = 3

Answer 2

This is a very primitive way of updating the desired row. Considering that the table was declared as tab in the DB you can actually JOIN it with a subquery filtered from the table itself without using an ON and then setting your desired variables accordingly.

UPDATE  tab JOIN  (SELECT * FROM tab WHERE ID = 3) AS temp SET   tab.COL1 = temp.COL1, tab.COL2 = temp.COL2, tab.COL3 = temp.COL3 WHERE tab.ID = 2