如何在SQL中将两列连接成一个新列？

Question

I have a problem while merging two columns into a new one. I just want to concatenate the columns IBAN and Currency_code into CheckSum. And when I make a SELECT * it appears.

DROP TABLE IF EXISTS transaccio;
CREATE TABLE transaccio (
   IBAN varchar(255),
   Currency_code varchar (255),
   CheckSum varchar(255)
);

I have raised two options, but none of them works.

Option one:

INSERT INTO transaccio(CheckSum) SELECT (CONCAT(IBAN, Currency_code)) FROM transaccio;

Option two: (it says that don't know from where get the IBAN and Currency_code)

INSERT INTO transaccio(CheckSum) VALUES (CONCAT(IBAN, Currency_code));

Answer 1

You need to use Update query instead of Insert :

UPDATE transaccio 
SET CheckSum = CONCAT(IBAN, Currency_code);

However it seems to be a Generated Column problem. Depending on your MySQL version, you could use Generated Columns instead.

PostgreSQL does not support Generated Columns / Virtual Columns natively yet . You may refer this answer: https://dba.stackexchange.com/a/183265/27070 to emulate them in PostgreSQL

Answer 2

You will need the UPDATE statement:

UPDATE transaccio
SET CheckSum = CONCAT(IBAN, Currency_code);