How are auto_increment keys handled in INSERT (SELECT * FROM...)

You can insert into an auto-increment column and specify a value. This is fine; it simply overrides the auto-increment generator.

If you try to insert a value of NULL or 0 or DEFAULT, or if you omit the auto-increment column from the columns in your INSERT statement, this activates the auto-increment generator.

So, it's fine to INSERT INTO table1 SELECT * FROM table2 (by the way, you don't need the parentheses). This means that the id values in table2 will be copied verbatim, and table1 will not generate new values.

If you want table1 to generate new values, you can't do SELECT *. Either you use null or 0 for the id column:

INSERT INTO table1 SELECT 0, col1, col2, col3, ... FROM table2;

Or else you omit the column from both the INSERT statement's column list and the SELECT statement's select-list:

-- No id in either case:
INSERT INTO table1 (col1, col2, col3) SELECT col1, col2, col3, ... FROM table2;

Before you ask, there is no syntax in SQL for "select * except for one column". You have to spell out the full list of column names you want to insert.

The id from the select will be the same value inserted into the table. This will result in an error if you're trying to duplicate existing rows.

Bill Karwin: Before you ask, there is no syntax in SQL for "select * except for one column".

This can be achieved with some creativity:

SET @sql = CONCAT('INSERT INTO <table> SELECT null, 
    ', (SELECT GROUP_CONCAT(COLUMN_NAME) 
    FROM information_schema.columns 
    WHERE table_schema = '<database>' 
    AND table_name = '<table>' 
    AND column_name NOT IN ('id')), ' 
from <table> WHERE id = <id>');  

PREPARE stmt1 FROM @sql;
EXECUTE stmt1;

This will result in the new row getting an auto incremented id instead of the id from the selected row.