Python PostgreSQL psycopg2将列连接到新列

Question

I can concateante two columns using the following code:

engine = create_engine(f'postgresql+psycopg2://user:password@host/db')
result = engine.execute('SELECT concat(col_1, col_2) AS uid FROM db_table;')

and I can alter the table to create a new column:

engine.execute('ALTER TABLE db_table 
ADD COLUMN concat_1_2 VARCHAR NOT NULL;')

But how can I insert the result query into the table in an efficient way (very large number of rows)?

Answer 1

if you need only an insert you could use an insert select

insert into db_table (concat_1_2 )
SELECT concat(col_1, col_2) 
FROM db_table

otherwise just use an update

UPDATE db_table
SET  concat_1_2 = concat(col_1, col_2) 

Answer 2

If you want to replace columns col_1 and col_2 with new one col_1_2 , you can alter the table in this way:

alter table db_table alter col_1 type varchar using concat(col_1, col_2);
alter table db_table rename col_1 to col_1_2;
alter table db_table drop col_2;