是否可以从 select 查询创建一个临时表并同时添加一组额外的列？

Question

I want to create a temporary table in one line using 3 columns + content from a existing table called affiliateproduct and at the same time add 2 columns title and content to the temporary table. Both need to be of type VARCHAR, however i cannot define these 2 columns explicitly in the same query. As a workaround i did the following:

       CREATE TEMPORARY TABLE affiliate_product_results ENGINE = MEMORY SELECT ap.id,
           ap.affiliateImageUrl, ap.rank, "" AS title, "" AS content FROM affiliateproduct ap; 

This results in a table that includes the 3 columns from affiliateproduct with corresponding types, but title and content both get the type char(0) assigned. That is not the type that i want. (It should be varchar(255) instead). Is there a way to get this to work with the correct type assignment? (I know i could probably assign a value of " " or something and then it would become a varchar(n spaces) but thats rather hacky.

Is there a way or am i forced to do an extra column insert query after the temporary table creation.

Thank you.

EDIT: I found a way to do it but its hacky. It goes like this:

       CREATE TEMPORARY TABLE affiliate_product_results ENGINE = MEMORY SELECT ap.id,
           ap.affiliateImageUrl, ap.rank, ap.affiliateImageUrl AS title, ap.affiliateImageUrl AS content FROM affiliateproduct ap; 

Now title and content get the same columntype as affiliateimageUrl (varchar255)

Answer 1

You can get a VARCHAR column using SPACE with TRIM :

CREATE TEMPORARY TABLE affiliate_product_results ENGINE = MEMORY 
SELECT ap.id, ap.affiliateImageUrl, ap.rank, 
  TRIM(SPACE(255)) AS title, 
  TRIM(SPACE(255)) AS content
FROM affiliateproduct

In case you want to initialize the new VARCHAR columns with NULL :

CREATE TEMPORARY TABLE affiliate_product_results ENGINE = MEMORY 
SELECT ap.id, ap.affiliateImageUrl, ap.rank, 
  IF(TRIM(SPACE(255)) = '', NULL, TRIM(SPACE(255))) AS title, 
  IF(TRIM(SPACE(255)) = '', NULL, TRIM(SPACE(255))) AS content
FROM affiliateproduct

You can adjust the size of the VARCHAR column with the parameter on SPACE .

demo on dbfiddle.uk