试图在 Oracle SQL 中将 FULL_NAME 分成 FIRST_NAME 和 LAST_NAME，但它没有显示表本身的任何更改

Question

This code is supposed to separate full name and it does. This code works fine, except for the fact that it does not add the data to the table.

SELECT FULL_NAME
SUBSTR(FULL_NAME, 1, INSTR(FULL_NAME, ' ', 1, 1)-1) as FIRST_NAME,
SUBSTR(FULL_NAME, INSTR(FULL_NAME, ' ', -1)+1) as LAST_NAME
from customers;

This code runs similarly but again, does not populate the table.

ALTER TABLE CUSTOMERS;

SELECT
    substr("A1"."FULL_NAME", 1, instr("A1"."FULL_NAME", ' ', 1, 1) - 1)                 "FIRST_NAME",
    substr("A1"."FULL_NAME", instr("A1"."FULL_NAME", ' ',(- 1)) + 1)                    "LAST_NAME"
FROM
    "XXXX"."CUSTOMERS" "A1";

This is what my query result is, it shows that everything is how it should be.

This is what my table looks like but as you can see, the last two columns do not have any data.

My goal is to be able to drop the FULL_NAME column, but I need these two split first and I am not sure why it is not working. Any help is appreciated.

Answer 1

A SELECT statement only displays data. It does not change it. ALTER TABLE is a DDL command that would actually change the structure of the table (like add a column), but you have not told it what to do; it does not change data. Use UPDATE to change data values:

UPDATE CUSTOMERS SET
    FIRST_NAME = SUBSTR(FULL_NAME, 1, INSTR(FULL_NAME, ' ', 1, 1)-1),
    LAST_NAME = SUBSTR(FULL_NAME, INSTR(FULL_NAME, ' ', -1)+1);
COMMIT;

Answer 2

You can use generated columns:

ALTER TABLE CUSTOMERS
    ADD FIRST_NAME AS substr("FULL_NAME", 1, instr("FULL_NAME", ' ', 1, 1) - 1);

ALTER TABLE CUSTOMERS
    ADD LAST_NAME AS  substr("FULL_NAME", instr("FULL_NAME", ' ',(- 1)) + 1) ;

These are calculated when they are references so the values are always up-to-date. No UPDATE is needed.

Note: I strongly, strongly discourage you from using double quotes for column names. There is no need for them.

Here is a db<>fiddle.