I need help in database design.
I have following tables.
Pseudo code:
Table order_status {
id int[pk, increment]
name varchar
}
Table order_status_update {
id int[pk, increment]
order_id int[ref: > order.id]
order_status_id int[ref: > order_status.id]
updated_at datetime
}
Table order_category {
id int[pk, increment]
name varchar
}
Table file {
id int[pk, increment]
order_id int[ref: > order.id]
key varchar
name varchar
path varchar
}
Table order {
id int [pk] // primary key
order_status_id int [ref: > order_status.id]
order_category_id int [ref: > order_category.id]
notes varchar
attributes json // no of attributes is not fixed, hence needed a json column
}
Everything was okay, but now I need an auto-increment id for each type of order_category_id column.
For example, if I have 2 categories electronics and toys , then I would need electronics-1, toy-1, toy-2, electronics-2, electronics-3, toy-3, toy-4, toy-5 values associated with rows of order table. But it's not possible as auto-increment increments based on each new row, not column type.
In other words, for table order instead of
id order_category_id
---------------------
1 1
2 1
3 1
4 2
5 1
6 2
7 1
I need following,
id order_category_id pretty_ids
----------------------------
1 1 toy-1
2 1 toy-2
3 1 toy-3
4 2 electronics-1
5 1 toy-4
6 2 electronics-2
7 1 toy-5
What I tried:
I created separate table for each order category (not an ideal solution but currently I have 6 order categories, so it works for now )
Now, I have table for electronics_order and toys_order. Columns are repetitive, but it works. But now I have another problem, my every relationship with other tables got ruined. Since, both electronics_order and toys_orders can have same id, I cannot use id column to reference order_status_update, order_status, file tables.
I can create another column order_category in each of these tables, but will it be the right way? I am not experienced in database design, so I would like to know how others do it.
I also have a side question.
Do I need tables for order_category and order_status just to store names? Because these values will not change much and I can store them in code and save in columns of order table.
I know separate tables are good for flexibility, but I had to query database 2 times to fetch order_status and order_category by name before inserting new row to order table. And later it will be multiple join for querying order table.
--
If it helps, I am using flask-sqlalchemy in backend and postgresql as database server.
In order to track the increment id which is based on the order_category, we can keep track of this value on another table. Let us call this table: order_category_sequence. To show my solution, I just created simplified version of order table with order_category.
CREATE TABLE order_category (
id SERIAL PRIMARY KEY,
name VARCHAR(100) NULL
);
CREATE TABLE order_category_sequence (
id SERIAL PRIMARY KEY,
order_category_id int NOT NULL,
current_key int not null
);
Alter Table order_category_sequence Add Constraint "fk_order_category_id" FOREIGN KEY (order_category_id) REFERENCES order_category (id);
Alter Table order_category_sequence Add Constraint "uc_order_category_id" UNIQUE (order_category_id);
CREATE TABLE "order" (
id SERIAL PRIMARY KEY,
order_category_id int NOT NULL,
pretty_id VARCHAR(100) null
);
Alter Table "order" Add Constraint "fk_order_category_id" FOREIGN KEY (order_category_id) REFERENCES order_category (id);
The order_category_id column in order_category_sequence table refers the order_category. The current_key column holds the last value in order.
When a new order row is added, we can use a trigger to read the last value from order_category_sequence and update pretty_id. The following trigger definition can be used to achieve this.
--function called everytime a new order is added
CREATE OR REPLACE FUNCTION on_order_created()
RETURNS trigger AS
$BODY$
DECLARE
current_pretty_id varchar(100);
BEGIN
-- increment last value of the corresponding order_category_id in the sequence table
Update order_category_sequence
set current_key = (current_key + 1)
where order_category_id = NEW.order_category_id;
--prepare the pretty_id
Select
oc.name || '-' || s.current_key AS current_pretty_id
FROM order_category_sequence AS s
JOIN order_category AS oc on s.order_category_id = oc.id
WHERE s.order_category_id = NEW.order_category_id
INTO current_pretty_id;
--update order table
Update "order"
set pretty_id = current_pretty_id
where id = NEW.id;
RETURN NEW;
END;
$BODY$ LANGUAGE plpgsql;
CREATE TRIGGER order_created
AFTER INSERT
ON "order"
FOR EACH ROW
EXECUTE PROCEDURE on_order_created();
If we want to synchronize the two table, order_category and order_category_sequence, we can use another trigger to have a row in the latter table every time a new order category is added.
//function called everytime a new order_category is added
CREATE OR REPLACE FUNCTION on_order_category_created()
RETURNS trigger AS
$BODY$
BEGIN
--insert a new row for the newly inserted order_category
Insert into order_category_sequence(order_category_id, current_key)
values (NEW.id, 0);
RETURN NEW;
END;
$BODY$ LANGUAGE plpgsql;
CREATE TRIGGER order_category_created
AFTER INSERT
ON order_category
FOR EACH ROW
EXECUTE PROCEDURE on_order_category_created();
Testing query and result:
Insert into order_category(name)
values ('electronics'),('toys');
Insert into "order"(order_category_id)
values (1),(2),(2);
select * from "order";
Regarding your side question, I prefer to store the lookup values like order_status and order_category in separate tables. Doing this allows to have the above flexibility and it is easy when we have changes.
To answer your side question: yes, you should keep tables with names in them, for a number of reasons. First of all, such tables are small and generally kept in memory by the database, so there is negligible performance benefit to not using the tables. Second, you want to be able to use external tools to query the database and generate reports, and you want these kind of labels available to those tools. Third, you want to minimize the coupling of your software to the actual data so that they can evolve independently. Adding a new category should not require modifying your software.
Now, to the main question, there is no built-in facility for the kind of auto-increment you want. You have to build it yourself.
I suggest you keep the sequence number for each category as a column in the category table. Then you can update it and use the updated sequence number in the order table, like this (which is specific to PostgreSQL):
-- set up the tables
create table orders (
id SERIAL PRIMARY KEY,
order_category_id int,
pretty_id VARCHAR
);
create unique index order_category_pretty_id_idx
on orders (pretty_id);
create table order_category (
id SERIAL PRIMARY KEY,
name varchar NOT NULL,
seq int NOT NULL default 0
);
-- create the categories
insert into order_category
(name) VALUES
('toy'), ('electronics');
-- create orders, specifying the category ID and generating the pretty ID
WITH
new_category_id (id) AS (VALUES (1)), -- 1 here is the category ID for the new order
pretty AS (
UPDATE order_category
SET seq = seq + 1
WHERE id = (SELECT id FROM new_category_id)
RETURNING *
)
INSERT into orders (order_category_id, pretty_id)
SELECT new_category_id.id, concat(pretty.name, '-', pretty.seq)
FROM new_category_id, pretty;
You just plug in your category ID where I have 1 in the example and it will create the new pretty_id for that category. The first category will be toy-1, the next toy-2, etc.
| id | order_category_id | pretty_id |
| --- | ----------------- | ------------- |
| 1 | 1 | toy-1 |
| 2 | 1 | toy-2 |
| 3 | 2 | electronics-1 |
| 4 | 1 | toy-3 |
| 5 | 2 | electronics-2 |
In order to do toys-1 toys-2 toys-3 you should repeat the logic of order_status update, There is no difference between track some status by time or by count.
Just in the order_status update it is simpler you just put now() into updated_at for lets say order_category_track you would take last value + 1 or have different sequences respectively category (would not recommend to do like this because it binds database objects with data in the DB).
I would change a schema to:
In this schema might be in inconsistent state. But in my opinion in your application there are three different entities "order","order_status","order category track" which live their own lives.
And still it is almost impossible to achieve consistent state for this task with out locks for example. This task is complicated by condition that next rows depends on previous what contradicts with SQL.
I would suggest to split category into 2-level hierarchy: category (toy, electronic) and subcategory (toy-1, toy-2, electronic-1, etc.):
So you can use column order_subcategory.full_name contain compiled "toy-1" value, or you can create view to make this field on the fly:
select oc.name || "-" || os.number
from order_category as oc
join order_subcategory as os on oc.id = os.category_id
https://dbdiagram.io/d/5dd6a132edf08a25543e34f8
Regarding your questions "Do I need tables for order_category and order_status just to store names?":
It is best practice to store this kind of data as a separate dictionary table. It gives you consistency and reliability. Querying those tables is very fast and easy for RDBMS, so feel free to use it.
I'll focus on only 3 tables you showed: order, order_status and order_category.
Creating a new table for a new record is not the right way. As your explanation, I think you trying to use order and order_category tables as many to many relationship. If it's so, the thing you need is a pivot table like this:
I currently add order_status column in order table,
you can add this column one of these tables as your need.
side question:
for order_status, if order status is fixed,( like only ACTIVE,INACTIVE and it won't be more values in the future) it would be better to use a column with ENUM type.
The easy answer would be to answer directly to your question. But I do not think it is a good thing in this case. So I will do otherwise.
I think that maybe the whole conception is wrong.
First things first : clarification of your business needs and assertions.
One order can have multiple categories
One category can concern multiple orders
One order can only have one status at a time but multiple through time
One status can be used by multiple orders
One order correspond to a file (probably a billing proof)
One file concerns only one order
Second : Advices
There is a little amount of reserved key words that you must not use in production environment. (https://www.postgresql.org/docs/current/sql-keywords-appendix.html). So for example I replace the word 'order' by 'command'.
Remaining questions that mandatory needs an answer before production : why the attributes attribute in your 'order' table? There is a risk of non respect of normal forms here. (https://www.geeksforgeeks.org/normal-forms-in-dbms/)
Third : conception solution
This normally is enough to give you a good start. But I wanna have fun a little more :) So...
Fourth : interrogation on needed performance
estimation of load per day/month in order (ten million rows per month?)
Fifth : physical solution proposition
Archiving in another tablespace (trigger when cancel or terminated => archived)
Indexes in another tablespace (your dba will thank you for that)
Possible partitionning of order table (https://pgxn.org/dist/pg_partman/doc/pg_partman.html, https://www.postgresql.org/docs/current/ddl-partitioning.html)
Hardware and option choosings (high availibility? disaster management? if it is: the elaboration needs further study but few)
Data transposition (is it really needed? if it is: the elaboration needs further study but few)
The finaaaaaal code-down ! (with the good music)
-- as a postgres user
CREATE DATABASE command_system;
CREATE SCHEMA in_prgoress_command;
CREATE SCHEMA archived_command;
--DROP SCHEMA public;
-- create tablespaces on other location than below
CREATE TABLESPACE command_indexes_tbs location 'c:/Data/indexes';
CREATE TABLESPACE archived_command_tbs location 'c:/Data/archive';
CREATE TABLESPACE in_progress_command_tbs location 'c:/Data/command';
CREATE TABLE in_prgoress_command.command
(
id bigint /*or bigserial if you use a INSERT RETURNING clause*/ primary key
, notes varchar(500)
, fileULink varchar (500)
)
TABLESPACE in_progress_command_tbs;
CREATE TABLE archived_command.command
(
id bigint /*or bigserial if you use a INSERT RETURNING clause*/ primary key
, notes varchar(500)
, fileULink varchar (500)
)
TABLESPACE archived_command_tbs;
CREATE TABLE in_prgoress_command.category
(
id int primary key
, designation varchar(45) NOT NULL
)
TABLESPACE in_progress_command_tbs;
INSERT INTO in_prgoress_command.category
VALUES (1,'Toy'), (2,'Electronic'), (3,'Leather'); --non-exaustive list
CREATE TABLE in_prgoress_command.status
(
id int primary key
, designation varchar (45) NOT NULL
)
TABLESPACE in_progress_command_tbs;
INSERT INTO in_prgoress_command.status
VALUES (1,'Shipping'), (2,'Cancel'), (3,'Terminated'), (4,'Payed'), (5,'Initialised'); --non-exaustive list
CREATE TABLE in_prgoress_command.command_category
(
id bigserial primary key
, idCategory int
, idCommand bigint
)
TABLESPACE in_progress_command_tbs;
ALTER TABLE in_prgoress_command.command_category
ADD CONSTRAINT fk_command_category_category FOREIGN KEY (idCategory) REFERENCES in_prgoress_command.category(id);
ALTER TABLE in_prgoress_command.command_category
ADD CONSTRAINT fk_command_category_command FOREIGN KEY (idCommand) REFERENCES in_prgoress_command.command(id);
CREATE INDEX idx_command_category_category ON in_prgoress_command.command_category USING BTREE (idCategory) TABLESPACE command_indexes_tbs;
CREATE INDEX idx_command_category_command ON in_prgoress_command.command_category USING BTREE (idCommand) TABLESPACE command_indexes_tbs;
CREATE TABLE archived_command.command_category
(
id bigserial primary key
, idCategory int
, idCommand bigint
)
TABLESPACE archived_command_tbs;
ALTER TABLE archived_command.command_category
ADD CONSTRAINT fk_command_category_category FOREIGN KEY (idCategory) REFERENCES in_prgoress_command.category(id);
ALTER TABLE archived_command.command_category
ADD CONSTRAINT fk_command_category_command FOREIGN KEY (idCommand) REFERENCES archived_command.command(id);
CREATE INDEX idx_command_category_category ON archived_command.command_category USING BTREE (idCategory) TABLESPACE command_indexes_tbs;
CREATE INDEX idx_command_category_command ON archived_command.command_category USING BTREE (idCommand) TABLESPACE command_indexes_tbs;
CREATE TABLE in_prgoress_command.command_status
(
id bigserial primary key
, idStatus int
, idCommand bigint
, change_timestamp timestamp --anticipate if you can the time-zone problematic
)
TABLESPACE in_progress_command_tbs;
ALTER TABLE in_prgoress_command.command_status
ADD CONSTRAINT fk_command_status_status FOREIGN KEY (idStatus) REFERENCES in_prgoress_command.status(id);
ALTER TABLE in_prgoress_command.command_status
ADD CONSTRAINT fk_command_status_command FOREIGN KEY (idCommand) REFERENCES in_prgoress_command.command(id);
CREATE INDEX idx_command_status_status ON in_prgoress_command.command_status USING BTREE (idStatus) TABLESPACE command_indexes_tbs;
CREATE INDEX idx_command_status_command ON in_prgoress_command.command_status USING BTREE (idCommand) TABLESPACE command_indexes_tbs;
CREATE UNIQUE INDEX idxu_command_state ON in_prgoress_command.command_status USING BTREE (change_timestamp, idStatus, idCommand) TABLESPACE command_indexes_tbs;
CREATE OR REPLACE FUNCTION sp_trg_archiving_command ()
RETURNS TRIGGER
language plpgsql
as $function$
DECLARE
BEGIN
-- Copy the data
INSERT INTO archived_command.command
SELECT *
FROM in_prgoress_command.command
WHERE new.idCommand = idCommand;
INSERT INTO archived_command.command_status (idStatus, idCommand, change_timestamp)
SELECT idStatus, idCommand, change_timestamp
FROM in_prgoress_command.command_status
WHERE idCommand = new.idCommand;
INSERT INTO archived_command.command_category (idCategory, idCommand)
SELECT idCategory, idCommand
FROM in_prgoress_command.command_category
WHERE idCommand = new.idCommand;
-- Delete the data
DELETE FROM in_prgoress_command.command_status
WHERE idCommand = new.idCommand;
DELETE FROM in_prgoress_command.command_category
WHERE idCommand = new.idCommand;
DELETE FROM in_prgoress_command.command
WHERE idCommand = new.idCommand;
END;
$function$;
DROP TRIGGER IF EXISTS t_trg_archiving_command ON in_prgoress_command.command_status;
CREATE TRIGGER t_trg_archiving_command
AFTER INSERT
ON in_prgoress_command.command_status
FOR EACH ROW
WHEN (new.idstatus = 2 or new.idStatus = 3)
EXECUTE PROCEDURE sp_trg_archiving_command();
CREATE TABLE archived_command.command_status
(
id bigserial primary key
, idStatus int
, idCommand bigint
, change_timestamp timestamp --anticipate if you can the time-zone problematic
)
TABLESPACE archived_command_tbs;
ALTER TABLE archived_command.command_status
ADD CONSTRAINT fk_command_command_status FOREIGN KEY (idStatus) REFERENCES in_prgoress_command.category(id);
ALTER TABLE archived_command.command_status
ADD CONSTRAINT fk_command_command_status FOREIGN KEY (idCommand) REFERENCES archived_command.command(id);
CREATE INDEX idx_command_status_status ON archived_command.command_status USING BTREE (idStatus) TABLESPACE command_indexes_tbs;
CREATE INDEX idx_command_status_command ON archived_command.command_status USING BTREE (idCommand) TABLESPACE command_indexes_tbs;
CREATE UNIQUE INDEX idxu_command_state ON archived_command.command_status USING BTREE (change_timestamp, idStatus, idCommand) TABLESPACE command_indexes_tbs;
Conclusion:
In many cases, when you are worried by the disposition of your keys it is because they are not in the good place. Same goes for cars ones! :D
Do not take any solution as prophetic solution : benchmark it.
So, Here is the condition.
I have a User_tbl whose code is as follow
CREATE TABLE Users_tbl (
id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT,
user_type INT
);
user_type is either 0,1 or 2 .. If it is 0 then it is player , 1 is for coach and 2 is for audience.
Now, I want to create a new table which has lists of coach inside it . Whose schema will be
CREATE TABLE coach_tbl(
coach_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT
)
and what I need is that, when the entry which is placed in Users_tbl has user_type =1 then it should Trigger one other query which will create an entry in coach_tbl and fill the columns. It should happen dynamically .
The following TRIGGER would accomplish what you want :-
CREATE TRIGGER setup_coach
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coach_tbl (username, password) VALUES(new.username,new.password);
END
;
The following was used for testing the above :-
DROP TABLE IF EXISTS Users_tbl;
CREATE TABLE IF NOT EXISTS Users_tbl (
id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT,
user_type INT
);
DROP TABLE IF EXISTS coach_tbl;
CREATE TABLE IF NOT EXISTS coach_tbl(
coach_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT
);
CREATE TRIGGER setup_coach
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coach_tbl (username, password) VALUES(new.username,new.password);
END
;
INSERT INTO Users_tbl (username, password,user_type)
VALUES
('Fred','fred1234',0),
('Bert','bert1234',1),
('Harold','harold1234',0),
('Alan','alan1234',1);
The result being :-
Supplementary (aka Why not the above)
Storing the exact same values. i.e. duplicating them, is contrary to normalisation and could lead to issues. e.g. if (using the above) "Bert"'s name or "password" changed you'd have to change it in two places. As it stands there is no need to duplicate this data as it would be easily available
For example, if you wanted to list the coaches you could use :-
SELECT username FROM coach_tbl;
Using the following, though, returns exactly the same but without the additional table :-
SELECT username FROM Users_tbl WHERE user_type = 1;
Supposing you had coach specific information say for example the number of times coaching then you could have an additional table such as :-
CREATE TABLE IF NOT EXISTS coaching_information
(
user_id_reference INTEGER REFERENCES Users_tbl(id),
number_of_times_coaching INTEGER DEFAULT 0
)
;
Along with a TRIGGER to automatically add default coaching information :-
CREATE TRIGGER autoadd_coaching_information_entry
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coaching_information
(user_id_reference)
VALUES (new.id)
;
END
;
Note! no need to set the number_of_times_coaching column as it will default to 0.
Assuming that all TABLES have been emptied then using (again):-
INSERT INTO Users_tbl (username, password,user_type)
VALUES
('Fred','fred1234',0),
('Bert','bert1234',1),
('Harold','harold1234',0),
('Alan','alan1234',1);
results in :-
2 refers to Bert, 4 to Alan
You could then list all coaches who have not coached (chosen for laziness of not having to update coaching inforamtion) :-
SELECT 'Coach '||username||' is up for a coaching experience.' AS coaching_needed
FROM coaching_information
JOIN Users_tbl ON Users_tbl.id = coaching_information.user_id_reference
WHERE coaching_information.number_of_times_coaching < 1
The result would be :-
Say Bert changed name to Charles e.g. using UPDATE Users_tbl SET username = 'Charles' WHERE username = 'Bert';
Then just with the 1 change the results from the above query would be :-
The full SQL used for testing the above was :-
DROP TABLE IF EXISTS coach_tbl;
DROP TABLE IF EXISTS Users_tbl;
CREATE TABLE IF NOT EXISTS Users_tbl (
id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT,
user_type INT
);
DROP TRIGGER IF EXISTS setup_coach; -- get rid of defunct TRIGGER
CREATE TABLE IF NOT EXISTS coaching_information
(
user_id_reference INTEGER REFERENCES Users_tbl(id) ON DELETE CASCADE,
-- Note ON DELETE CASCADE will automatically delete a coach should
-- the coach's User_tbl entry be deleted i.e. the deletion is propoagted
-- to the children of the parent.
-- (could also use ON UPDATE CASCADE but unlikely to change the underlying id)
number_of_times_coaching INTEGER DEFAULT 0
)
;
DROP TRIGGER IF EXISTS autoadd_coaching_information_entry;
CREATE TRIGGER autoadd_coaching_information_entry
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coaching_information
(user_id_reference)
VALUES (new.id)
;
END
;
INSERT INTO Users_tbl (username, password,user_type)
VALUES
('Fred','fred1234',0),
('Bert','bert1234',1),
('Harold','harold1234',0),
('Alan','alan1234',1)
;
--
-- Note! oncommmenting this will change Bert's name to Charles
--UPDATE Users_tbl SET username = 'Charles' WHERE username = 'Bert';
--
SELECT 'Coach '||username||' is up for a coaching experience.' AS coaching_needed
FROM coaching_information
JOIN Users_tbl ON Users_tbl.id = coaching_information.user_id_reference
WHERE coaching_information.number_of_times_coaching < 1
I am beginner in sql.I am using sqlplus to run the sql query .I used simple query but it shows an error like "MISSING RIGHT PARENTHESIS".My objective is to create the autoincrement primary key .Can anyone solve the error?Thanks in advance...
create table student(rollno int identity(1,1) primary key,
name varchar(20),marks int);
For Oracle, the rollno column could be defined as NUMBER(0010) and primary key.
Then you would need to add an ON INSERT trigger to populate rollno from a SEQUENCE. There are many samples of triggers and sequences on this site.
In oracle 12 you can use a identity column to automatically fill your ID
CREATE TABLE students
(
"ID" NUMBER GENERATED BY DEFAULT AS IDENTITY MINVALUE 1 MAXVALUE 9999999999
INCREMENT BY 1 START WITH 1 ,
"NAME" VARCHAR2(20),
"MARKS" NUMBER(2,0),
CONSTRAINT PK_STUDENTS PRIMARY KEY (ID) ENABLE
);
/
This creates a table without any triggers needed and automatically fills the id column (of not specified with a value) with the next number up to 99999...
If you're using oracle 11 and below, you need a trigger on insert and assign a value (custom_sequence.nextval) to the id column.
CREATE TABLE students
(
"ID" NUMBER(5,0) not null,
"NAME" VARCHAR2(20),
"MARKS" NUMBER(2,0),
CONSTRAINT PK_STUDENTS PRIMARY KEY (ID) ENABLE
);
/
CREATE SEQUENCE SEQ_STUDENTS INCREMENT BY 1 START WITH 1;
/
TRIGGER TC_students
before insert on students
for each row
begin
if (:new.id is null) then
select SEQ_students.nextval into :new.id from dual;
end if;
end;
/
And please use VARCHAR2.
I want to be able to label the database with a single value, i.e its name, from within the database instead of my application, since it will always be one ID per database. For example, something like this:
DATABASE_A.sql
-- Database Name Table
CREATE TABLE database (
name VARCHAR(10) NOT NULL UNIQUE,
);
CREATE TABLE item (
id SERIAL PRIMARY KEY,
name VARCHAR(10) NOT NULL UNIQUE,
);
Insert Into database (name) values ('A');
DATABASE_B.sql
-- Database Name Table
CREATE TABLE database (
name VARCHAR(10) NOT NULL UNIQUE,
);
CREATE TABLE item (
id SERIAL PRIMARY KEY,
name VARCHAR(10) NOT NULL UNIQUE,
);
Insert Into database (name) values ('B');
This is because when they are combined and stored on a SOLR search server their ID is a combination of their database name and their item ID, such as this:
SOLR ITEM ID's
A1
A2
A3
B1
Is it ok to have a single table to define the prefix so that when I do the look up from my SQL website to SOLR I can just do the following query:
database (name) + item (id) = SolrID
I'd be more inclined to build a procedure in each database that contained the database ID, for example:
CREATE OR REPLACE FUNCTION solrid(IN local_id INTEGER, OUT result TEXT) AS $$
DECLARE
database_id TEXT := 'A';
BEGIN
result := database_id || local_id::TEXT;
END;
$$ LANGUAGE PLPGSQL;
Then you could write your select statement like:
SELECT solrid(id), name FROM item;
which seems to be a cleaner solution.
I would like to achieve an identity or auto-incrementing value in a column ala SQL Server:
CREATE TABLE RollingStock
(
Id NUMBER IDENTITY(1,1),
Name Varchar2(80) NOT NULL
);
How can this be done?
As Orbman says, the standard way to do it is with a sequence. What most people also do is couple this with an insert trigger. So, when a row is inserted without an ID, the trigger fires to fill out the ID for you from the sequence.
CREATE SEQUENCE SEQ_ROLLINGSTOCK_ID START WITH 1 INCREMENT BY 1 NOCYCLE;
CREATE OR REPLACE TRIGGER BI_ROLLINGSTOCK
BEFORE INSERT ON ROLLINGSTOCK
REFERENCING OLD AS OLD NEW AS NEW
FOR EACH ROW
WHEN (NEW.ID IS NULL)
BEGIN
select SEQ_ROLLINGSTOCK_ID.NEXTVAL
INTO :NEW.ID from dual;
END;
This is one of the few cases where it makes sense to use a trigger in Oracle.
If you really don't care what the primary key holds, you can use a RAW type for the primary key column which holds a system-generated guid in binary form.
CREATE TABLE RollingStock
(
ID RAW(16) DEFAULT SYS_GUID() PRIMARY KEY,
NAME VARCHAR2(80 CHAR) NOT NULL
);