使用sqlite3和python更新表中现有列的值

Question

I am trying to add a column from a table2 to my existing table1.

table1 looks like this (this is a 2 columns example but in reality I have more than 100):

id | item | price
-------------
 1 | book | 20  
 2 | copy | 30   
 3 | pen  | 10 

and table2 like this:

id | item 
----------
 1 | book 
 2 | copy 
 3 | pen  

I would like to get this:

id | item | price | item 
---------------------
 1 | book | 20    | book  
 2 | copy | 30    | copy   
 3 | pen  | 10    | pen  

However, I'm getting the following, all the same first row value:

id | item | price | item 
---------------------
 1 | book | 20    | book  
 2 | copy | 30    | book   
 3 | pen  | 10    | book  

What I am doing wrong in my code?

con = sqlite3.connect(":memory:")
cur = con.cursor()

cur.execute("ALTER TABLE table1 ADD COLUMN item text")
cur.execute("UPDATE table1 SET item = (SELECT item FROM table2 WHERE table2.id = id)")

Thanks!

Answer 1

You need a correlated subquery:

UPDATE table1
    SET item = (SELECT t2.item FROM table2 t2 WHERE t2.id = table1.id);

I am surprised that your version is not returning an error. The WHERE condition is interpreted as WHERE table2.id = table2.id , which means that all rows should be returned.