MySQL. Two tables, copy one column

Question

I am learning MySQL and I have an issue. I have two tables.. table1 and table2. table1 contains several columns such as (id, type, id_marca, price) etc and table2 has several columns such as (id, values, .., id_marca). What I want and what I'm trying to do is: id_marca in the first table has values and the id_marca in the second table has NULL values. I want to copy the values from id_marca.table1 into id_marca.table2. Basically copy the column in the first table into the second one.

I used

INSERT INTO table2 (id_marca) SELECT  id_marca  FROM table1 ;

But the issue is the following.. it inserts the values of the column in the first table AFTER the NULL values and does not replace them.

To see the issue better: This is table1:

id    name    id_marca
1      a         1
2      b         1 
3      c         2

This is table2:

id   value   id_marca
1      123         NULL
2      34155       NULL
3      123         NULL

After I execute INSERT INTO table2 (id_marca) SELECT id_marca FROM table1 , table 2 becomes:

id   value   id_marca
1      123         NULL
2      34155       NULL
3      123         NULL
4       0            1
5       0            1
6       0            2

But I want it to be:

id   value   id_marca
1      123         1
2      34155       1
3      123         2

Hope you will understand, thank you in advance guys.

Answer 1

You should use UPDATE not INSERT and if these tables is logically linked by ID field then try:

UPDATE TABLE2 a 
    JOIN TABLE1 b ON a.id = b.id
SET a.id_marca = b.id_marca

Answer 2

Context

• MySQL v 5.7
• User wants to copy one table column to another table using INSERT
• The goal is to change BEFORE into AFTER

Solution

• This can be accomplished using MySQL INSERT ON DUPLICATE KEY UPDATE
• This approach will insert new records, and it will also update existing records having matching ids

Example

INSERT INTO zzdemo_table02
  (lname,userid)
SELECT
  lname,userid
  FROM(
    SELECT
      lname,userid
    FROM
      zzdemo_table01
  ) as tt01
ON DUPLICATE KEY UPDATE
  userid=tt01.userid
  ,lname=tt01.lname
;

See also

• MySQL copy column with conditional