MySQL: How to copy rows, but change a few fields?

INSERT INTO Table
          ( Event_ID
          , col2
           ...
          )
     SELECT "155"
          , col2
           ...
      FROM Table WHERE Event_ID = "120"

Here, the col2, ... represent the remaining columns (the ones other than Event_ID) in your table.

This is a solution where you have many fields in your table and don't want to get a finger cramp from typing all the fields, just type the ones needed :)

How to copy some rows into the same table, with some fields having different values:

1. Create a temporary table with all the rows you want to copy
2. Update all the rows in the temporary table with the values you want
3. If you have an auto increment field, you should set it to NULL in the temporary table
4. Copy all the rows of the temporary table into your original table
5. Delete the temporary table

Your code:

CREATE table temporary_table AS SELECT * FROM original_table WHERE Event_ID="155";

UPDATE temporary_table SET Event_ID="120";

UPDATE temporary_table SET ID=NULL;

INSERT INTO original_table SELECT * FROM temporary_table;

DROP TABLE temporary_table;

General scenario code:

CREATE table temporary_table AS SELECT * FROM original_table WHERE <conditions>;

UPDATE temporary_table SET <fieldx>=<valuex>, <fieldy>=<valuey>, ...;

UPDATE temporary_table SET <auto_inc_field>=NULL;

INSERT INTO original_table SELECT * FROM temporary_table;

DROP TABLE temporary_table

Simplified/condensed code:

CREATE TEMPORARY TABLE temporary_table AS SELECT * FROM original_table WHERE <conditions>;

UPDATE temporary_table SET <auto_inc_field>=NULL, <fieldx>=<valuex>, <fieldy>=<valuey>, ...;

INSERT INTO original_table SELECT * FROM temporary_table;

As creation of the temporary table uses the TEMPORARY keyword it will be dropped automatically when the session finishes (as @ar34z suggested).

Let's say your table has two other columns: foo and bar

INSERT INTO Table (foo, bar, Event_ID)
SELECT foo, bar, "155"
  FROM Table
 WHERE Event_ID = "120"

If you have loads of columns in your table and don't want to type out each one you can do it using a temporary table, like;

SELECT *
INTO #Temp
FROM Table WHERE Event_ID = "120"
GO

UPDATE #TEMP
SET Column = "Changed"
GO

INSERT INTO Table
SELECT *
FROM #Temp

Hey how about to copy all fields, change one of them to the same value + something else.

INSERT INTO Table (foo, bar, Event_ID)
SELECT foo, bar, Event_ID+"155"
  FROM Table
 WHERE Event_ID = "120"

??????????