I use ms sql and i need to create a table with a array column of nvarchar. What is the correct query ?
You don't want an array column. You want a separate table (or perhaps a JSON/XML column, but I won't focus on that).
The normal method would be:
create table main (
main_id int identity primary key,
. . .
);
create table element (
element_id int identity primary key,
position int,
value varchar(255),
. . .
);
create table main_elements (
main_element_id int identity primary key,
main_id int references main(main_id),
element_id int references elements(element_id)
);
Related
I am new in Posgresql. I have 5 tables and I am trying to INSERT properties to tables. When I tried to Insert 2nd time, I have this error in 'pgadmin'.
ERROR: insert or update on table "question" violates foreign key constraint "question_id_difficulty_fkey" DETAIL: Key (id_difficulty)=(9) is not present in table "difficulty". SQL state: 23503.
my schema is here
id SERIAL PRIMARY KEY,
name varchar
);
CREATE TABLE question (
id SERIAL PRIMARY KEY,
text varchar,
correct_answer varchar,
incorrect_answer1 varchar,
incorrect_answer2 varchar,
incorrect_answer3 varchar,
id_difficulty SERIAL REFERENCES difficulty(id),
id_category SERIAL REFERENCES category (id),
id_creator SERIAL REFERENCES game (id)
);
CREATE TABLE difficulty (
id SERIAL PRIMARY KEY,
name varchar
);
CREATE TABLE category (
id SERIAL PRIAMRY KEY,
name varchar
);
CREATE TABLE user (
id SERIAL PRIMARY KEY,
name varchar
)
You would need a corresponding entry in the difficulty table with an id of 9, so that a referencing id_difficulty column in the question table.
For example, if your difficulty table contained:
id | name
----+----------------
1 | easy
2 | reasonable
3 | difficult
4 | very difficult
5 | impossible
You could only set id_difficulty for rows in the question table to one of those id values. If you set 6, or 12 or anything other than 1 to 5, it would fail because the values are constrained by the values in the foreign key.
The id_difficulty, id_category and id_creator columns shouldn't be using serial, so these should have their defaults dropped:
ALTER TABLE question ALTER COLUMN id_difficulty DROP DEFAULT;
ALTER TABLE question ALTER COLUMN id_category DROP DEFAULT;
ALTER TABLE question ALTER COLUMN id_creator DROP DEFAULT;
Postgres now recommends using generated always as instead of serial. If you do this, then the types will align much more simply:
CREATE TABLE question (
id int generated always as identity PRIMARY KEY,
text varchar,
correct_answer varchar,
incorrect_answer1 varchar,
incorrect_answer2 varchar,
incorrect_answer3 varchar,
id_difficulty int REFERENCES difficulty(id),
id_category int REFERENCES category (id),
id_creator int REFERENCES game (id)
);
CREATE TABLE difficulty (
id int generated always as identity PRIMARY KEY,
name varchar
);
This makes what is happening much clearer. The data type for a foreign key reference needs to match the data type of the primary key. Postgres knows that serial is really int. But using generated always, it is obvious that they are the same.
In addition, generated always as is more consistent with standard SQL.
Suppose I'm building a website that has users who can create "rooms" and add others to them. How would the rooms table keep track of its members without making a new table per room?
You would have two tables, one for rooms and one for members. They would be connected through foreign key relationships:
create table rooms (
room_id int primary key, -- auto-increment, serial, identity . . .
. . .
);
create table room_users (
room_user_id int primary key, -- auto-increment, serial, identity . . .
room_id int references rooms(room_id),
user_id int references users(user_id)
);
I am trying to make a simple database with an number generator but why do I get the error below?
ERROR: syntax error at or near "AUTO_INCREMENT"
LINE 2: IDNumber int NOT NULL AUTO_INCREMENT,
Code:
CREATE TABLE Finance
(
IDNumber int NOT NULL AUTO_INCREMENT,
FinName varchar(50) NOT NULL,
PRIMARY KEY(IDNumber)
);
The subject of the question mentions pgAdmin 4, so here's how to do it there.
First, add a column to your table, then click the little edit icon:
Then go to Constraints and select the Identity type:
This generates SQL similar to this:
CREATE TABLE public.my_table_name
(
id integer NOT NULL GENERATED ALWAYS AS IDENTITY,
PRIMARY KEY (id)
);
For Postgres you have to use SERIAL
CREATE TABLE Finance
(
IDNumber SERIAL PRIMARY KEY,
FinName varchar(50) NOT NULL
);
IN pgadmin-2.
step 01:
create seq:
and set info:
step 02: go to ID in table and set constraints
if it is sql the syntax is the following
CREATE TABLE Persons (
ID int IDENTITY(1,1) PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
You are using a MySQL syntax which won't work in SQL Server.
CREATE TABLE Finance
(
IDNumber int NOT NULL IDENTITY(1,1) PRIMARY KEY,
FinName varchar(50) NOT NULL
);
The following code should work for SQL Server.
IDENTITY(1,1) is SQL Server's way of saying "auto increment".
The starting value for IDENTITY is 1, and it will increment by 1 for each new record.
So : IDENTITY(startvalue, incrementvalue)
there are two options; one is to use the "datatype" serial or create a sequence and use this sequence as a default value for your integer as follows:
CREATE SEQUENCE your_seq;
CREATE TABLE foo(
id int default nextval('your_seq'::regclass),
other_column TEXT);
INSERT INTO foo(other_column) VALUES ('bar') RETURNING *;
It is important to note that specifying a table as follows:
CREATE TABLE tablename (
colname SERIAL);
is equivalent to:
CREATE SEQUENCE tablename_colname_seq AS integer;
CREATE TABLE tablename (
colname integer NOT NULL DEFAULT nextval('tablename_colname_seq'));
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;
More information about serial can be found here.
I'm trying to create 3 tables, but the table Award cannot be created. Within the brackets (Child, Present) I get an error. What should I do? Table Present and table Child are created but not table Award. I'm not able to create table Award, why?
create table Child
(
ID integer primary key,
name varchar(20) unique not null,
age integer,
kind bit
);
create table Presents
(
ID integer primary key,
name varchar(20) unique,
weight float
);
create table Award
(
ID integer primary key,
childID integer references Barn(ID),
presentID integer references Presenter(ID),
unique(Child, Present),
antal int
);
Child and Present are not columns in Award. I believe you want unique(childID, presentID)
I'm trying to create a hireiarchial table in postgres. I'm using the adjacent list-approach. My question is, how should I reference the ID of the same table when creating the data-model?
create table nodes (
id serial primary key,
parentid WHAT GOES HERE?
name varchar,
);
You can do:
create table nodes (
id serial primary key,
parentid integer references nodes(id),
name varchar
);
These are called "self-referencing tables"