如何在 INSERT SELECT 语句中使用 UPDATE

Question

I want to insert records from table2 to table1. I need to replace the records if a duplicate in the primary key is found. The primary key of a type string .

So my statement look like ( name is primary key and it is a string . Duplicate rows can arise from table2 , which I want to update):

INSERT INTO `myscheme1`.`table1`
(`table1`.`name`,
    `table1`.`id`,
    `table1`.`history`)

SELECT `table2`.`name`,
    `table2`.`id`,
    `table2`.`history`
FROM `myscheme2`.`table2`;

Where to add UPDATE ? If I can not use UPDATE , can you clarify how to use ON DUPLICATE KEY UPDATE ?

Because I do not get how to apply it? I do not know the new string of the primary key that I should update the old one with (it is being read by the command and I have many duplicate cases). So this example: below assumes I know what is the new value that I should input if a duplicate happens.

I prefer to use UPDATE so it replaces the old record with the new automatically.

INSERT INTO 
   devices(name) 
VALUES 
   ('Printer') 
ON DUPLICATE KEY UPDATE name = 'Printer';

Can you please show me how to edit my command syntax if I want to use UPDATE or ON DUPLICATE KEY UPDATE ?

Answer 1

You use ON DUPLICATE KEY UPDATE the same way whether the new values are coming from SELECT or VALUES .

INSERT INTO `myscheme1`.`table1`
(`table1`.`name`, `table1`.`id`,  `table1`.`history`)
SELECT `table2`.`name`, `table2`.`id`, `table2`.`history`
FROM `myscheme2`.`table2`
ON DUPLICATE KEY UPDATE id = VALUES(id), history = VALUES(history);

If table1 has the same name as a row in table2 , the other columns will be copied into that row.

You don't need to include the name column in ON DUPLICATE KEY . It already has the value from the other table, since that's what makes it a duplicate.