如何在 SQLite3 命令行中将字符串拆分为新列？

Question

I am constructing a simple table in SQLite3 using the following.sql script:

drop table if exists projects;

CREATE TABLE projects(
  "project_number" TEXT,
  "project_manager" TEXT
);

insert into projects ("project_manager", "project_number")
values ("Bob", "11204568-001");
insert into projects ("project_manager", "project_number")
values ("Bill", "11204568-002");
insert into projects ("project_manager", "project_number")
values ("Jack", "11204568-003");
insert into projects ("project_manager", "project_number")
values ("Jill", "11204000");
insert into projects ("project_manager", "project_number")
values ("Fred", "11204569");
insert into projects ("project_manager", "project_number")
values ("Nancy", "11204569-003");

I then add a column to this table called main_project_number using the alter table statement:

alter table projects add column "main_project_number" integer;

I would then like to populate this new column with only the prefix of the the project_number_column , such that I get a result like this:

project_number        project_manager  main_project_number
--------------------  ---------------  -------------------
11204568-001          Bob              11204568
11204568-002          Bill             11204568
11204568-003          Jack             11204568
11204000              Jill             11204000
11204569              Fred             11204569
11204569-003          Nancy            11204569

So I tried an update statement with some sqlite string functions as defined here :

update projects set main_project_number = (select substr("project_number", 0, instr("project_number", "-")) from projects);

This produced the following result, however, which is not what I want...:

project_number        project_manager  main_project_number
--------------------  ---------------  -------------------
11204568-001          Bob              11204568
11204568-002          Bill             11204568
11204568-003          Jack             11204568
11204000              Jill             11204568
11204569              Fred             11204568
11204569-003          Nancy            11204568

What am I doing wrong here?

Answer 1

Update should refer to specific row:

update projects 
set main_project_number = 
    CASE WHEN instr("project_number", "-") > 0 
         THEN substr("project_number", 0, instr("project_number", "-"))
         ELSE "project_number"
    END

db<>fiddle demo

---

If you are using SQLite 3.31.0 and above I suggest to use generated columns to avoid running update.

ALTER TABLE projects
ADD COLUMN main_project_number TEXT GENERATED ALWAYS AS
  (CASE WHEN instr("project_number", "-") > 0 
             THEN substr("project_number", 0, instr("project_number", "-"))
             ELSE "project_number"
        END) VIRTUAL;

Answer 2

If the column project_number does not have leading 0 s you can do it like this:

update projects 
set main_project_number =  project_number + 0;

See the demo .