Question

I want to create a MySQL table as a copy of another table like this:

CREATE TABLE new_tbl SELECT * FROM orig_tbl;

The twist is that I want, if possible, to add at the time of creation another empty column, that will be populated at a later time.

I know that I can just create it as above and use ALTER TABLE afterwards, but my thinking is that, given a large amount of data, the ALTER is gonna take a long time (please contradict me if this is wrong), that can be saved if what I want is possible.

So, say I want an extra extra_col - varchar(64), what would my original query be?

Thanks.

Answer 1

As documented under CREATE TABLE ... SELECT Syntax:

You can create one table from another by adding a SELECT statement at the end of the CREATE TABLE statement:

CREATE TABLE new_tbl SELECT * FROM orig_tbl;

MySQL creates new columns for all elements in the SELECT.

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Notice that the columns from the SELECT statement are appended to the right side of the table, not overlapped onto it.

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In a table resulting from CREATE TABLE ... SELECT, columns named only in the CREATE TABLE part come first. Columns named in both parts or only in the SELECT part come after that. The data type of SELECT columns can be overridden by also specifying the column in the CREATE TABLE part.

Therefore:

CREATE TABLE new_tbl (
  extra_col VARCHAR(64)
) SELECT * FROM orig_tbl