Using MySQL, I have the following SQL Table definition:
CREATE TABLE books (
author INT,
book INT,
name VARCHAR(128),
PRIMARY KEY(author, book)
);
What I want is that I have an Id for author that I set manually and an Id for book that is incremented for each author id. Therefore I created a trigger like so:
CREATE TRIGGER trBooks
BEFORE INSERT ON books
FOR EACH ROW SET NEW.book = (
SELECT COALESCE(MAX(book), -1) + 1 FROM books
WHERE author = NEW.author
);
This works fine for me. But now I need to know the book id that was set for my inserted entry that I inserted in Java. Something like the Insert with Output as in MSSQL or a Statement.executeQuery("INSERT ..."). The solution has to be thread safe, so a separate INSERT and SELECT is no good solution, since there might have been another INSERT in the meantime.
Thanks for your help!
Your data model just doesn't make sense. You have two entities, "books" and "authors". These should each be represented as a table. Because a book can have multiple authors and an author can write multiple books, you want a junction table.
This looks like this:
CREATE TABLE Books (
BookId INT auto_increment primary key,
Title VARCHAR(255)
);
CREATE TABLE Authors (
AuthorId INT auto_increment primary key,
Name VARCHAR(255)
);
CREATE TABLE BookAuthors (
BookAuthorId INT auto_increment primary key,
AuthorId INT,
BookId INT,
CONSTRAINT fk_BookAuthor_BookId FOREIGN KEY (BookId) REFERENCES Books(BookId),
CONSTRAINT fk_BookAuthor_AuthorId FOREIGN KEY (BookId) REFERENCES Authors(AuthorId),
UNIQUE (AuthorId, BookId)
);
As for your question about inserts. You don't need a trigger to set auto-incremented ids. You can use LAST_INSERT_ID() to fetch the most recent inserted value.
Related
If I have two tables with a simple many-to-one relationship:
CREATE TABLE parent (
id BIGINT PRIMARY KEY,
name VARCHAR(255)
)
CREATE TABLE child (
id BIGINT PRIMARY KEY,
name VARCHAR(255),
parent_id BIGINT FOREIGN KEY REFERENCES parent (id)
)
How can I query on the child table and convert the rows corresponding to the parent table to a Java Record easily with Jooq?
var a = dslContext.select(
PARENT.ID,
PARENT.NAME,
DSL.field(DSL.row(
PARENT.child().ID,
PARENT.child().NAME)
.convert(???)) // How can I convert sub-entities like this?
.fetch(Records.mapping(ChildDTO::new)); // This works fine for the top-level
It seems like something along those lines ^ should work, but I haven't been able to find it. Am I on the right track, or is there another approach I should be taking?
I think there's just a problem of reversed relationships here, where child and parent were confused. This should work?
dslContext
.select(
CHILD.ID,
CHILD.NAME,
row(CHILD.parent().ID, CHILD.parent().NAME).mapping(ParentDTO::new))
.from(CHILD)
.fetch(Records.mapping(ChildDTO::new))
THis example is using Row2.mapping(Function2), which is just convenience for an ad-hoc converter placed on the Row2 expression, which is a SelectField<Record2<T1, T2>> (there's no need to wrap it in DSL.field(...), explicitly)
I have a project, where bot_users play in game_tables. So I have a join table. I also store the buy_in (points available to the player at the table) in that join table. My SQL:
CREATE TABLE bot_users (
user_id bigint PRIMARY KEY,
free_points bigint CHECK (free_points >= 0),
frozen_points bigint CHECK (frozen_points >= 0)
);
CREATE TABLE game_tables (
channel_id bigint PRIMARY KEY,
owner bigint REFERENCES bot_users(user_id),
in_game boolean NOT NULL
);
CREATE TABLE game_tables_participants (
game_table_id bigint REFERENCES game_tables(channel_id),
participant_id bigint REFERENCES bot_users(user_id),
buy_in bigint NOT NULL,
PRIMARY KEY (game_table_id, participant_id)
);
My question now is: how do I represent that buy_in metadata in entities in Java? If buy_in didn't exist, I would simply have a ParticipantRef of which I would have a Set in the GameTable entity, and then have methods that work on IDs there. But I want to have buy_in available in the code too, so should I create a ParticipantRef-like entity that contains the buy_in? If yes, then how would persisting it work?
Your proposed solution is pretty much the way to do this. Instead of having a ParticipantRef with just the userId of the BotUsers it also gets a buyIn attribute.
Since you have an object references from GameTable via a Set to the ParticipantRef it will be considered part of the GameTable-Aggregate and get persisted whenever you persist a GameTable instance.
I am creating a program which is a Car Management app in Java using Swing in Netbeans, and as the database I am using Mysql, which will do all the CRUD operation. I have created a database with 3 different tables.
DATABASE SCHEMA
CREATE TABLE car_make(
make_id INT NOT NULL AUTO_INCREMENT
make VARCHAR(50)
PRIMARY KEY(make_id)
)
CREATE TABLE car_model(
model_id INT NOT NULL AUTO_INCREMENT
model VARCHAR(50)
fk_make_id INT
PRIMARY KEY(model_id)
FOREIGN KEY(fk_make_id) REFERENCES car_make(make_id)
)
CREATE TABLE car_attributes(
car_attr_id INT NOT NULL AUTO_INCREMENT
fk_make_id INT
fk_model_id INT
year INT
body_type VARCHAR(50)
mileage INT
price DECIMAL(6,2)
PRIMARY KEY(car_attr_id )
FOREIGN KEY(fk_make_id) REFERENCES car_make(make_id)
FOREIGN KEY(fk_model_id) REFERENCES car_model(model_id )
);
The car_make table is already populated with all the car makes which I inserted manually and their ID's were auto generated. And the car_model table is also populated with different models for each make.
I have also created the user interface in netbeans using Java Swing, where the user selects the make of the car which will automatically generate the corresponding model, the year, mileage and so on and insert all that data into the car_attribute tables. My question is, what is the query to insert the car make and model into the car_attribute table as foreign keys. For example if the user chooses as Make-BMW and Model-5 Series, I want to insert both of those IDS into the third table.
this scenario came up when you want to add new car, so the GUI show you the CAR_MAKEs
when you choose, it will show you CAR_MODELs, then you need to STORE the ID of fetched data (car_makes OR car_models) in arrayList and use it in the query when the USER submit
Just pseudo code
int carMakesSelectedIndex = comboCarMakes.getSelectedIndex();
int carModelsSelectedIndex = comboCarModels.getSelectedIndex();
PreparedStatement stmt=con.prepareStatement("insert into car_attributes values(?,?,?,?,?,?,?,?,?,?)");
stmt.setInt(1,carAttribute);
stmt.setInt(2,carMakesIdList.get( carMakesSelectedIndex ) );
stmt.setInt(3,carMakesIdList.get( carModelsSelectedIndex ) );
stmt.setString(4,carYear );
// the same with other attribute
I am using Hibernate Envers to audit some entities. I manually created the associated audit tables. However, I am having trouble determining what an audit table's primary key should be. For example, consider a fictional table designed to store customers:
CREATE TABLE CUSTOMER
(
CUSTOMER_ID INTEGER,
CUSTOMER_NAME VARCHAR(100),
PRIMARY KEY (CUSTOMER_ID)
)
And you create the audit table:
CREATE TABLE CUSTOMER_REVISION
(
REVISION_ID INTEGER,
REVISION_TYPE_ID INTEGER,
CUSTOMER_ID INTEGER,
CUSTOMER_NAME VARCHAR(100),
PRIMARY KEY (???)
)
Here were the options I considered:
Primary key: REVISION_ID
This cannot be the primary key because multiple entities of the same class may be modified during the same revision.
Primary key: (REVISION_ID, CUSTOMER_ID)
This seems more likely, but I'm not sure if Envers will insert multiple records per customer per revision.
Primary key: (REVISION_ID, REVISION_TYPE_ID, CUSTOMER_ID)
This seems like overkill, but it may be possible that Envers will insert different types of records (add, modify or delete) per customer per revision.
Primary key: A new column
Perhaps the primary key must simply be another column containing a synthetic primary key.
What is the true primary key of an audit table managed by Hibernate Envers?
Judging by the examples in the documentation, it appears that the primary key in my example would be (REVISION_ID, CUSTOMER_ID). Here is the example in the documentation:
create table Address (
id integer generated by default as identity (start with 1),
flatNumber integer,
houseNumber integer,
streetName varchar(255),
primary key (id)
);
create table Address_AUD (
id integer not null,
REV integer not null,
flatNumber integer,
houseNumber integer,
streetName varchar(255),
REVTYPE tinyint,
***primary key (id, REV)***
);
The primary key of audit table is the combination of original id(id) and revision number(rev) of the audit table.
As the official documentation there can be at most one historic entry for a given entity instance at a given revision, which simply means unique combination of above two column.
i have two tables where in the first one i have 14 millions and in the second one i have 1.5 million of data.
So i wonder how could i transfer this data to another table to be normalized ?
And how do i convert some type to another, for example: i have a field called 'year' but its type is varchar, but i want it an integer instead, how do i do that ?
I thought about do this using JDBC in a loop while from java, but i think this is not effeciently.
// 1.5 million of data
CREATE TABLE dbo.directorsmovies
(
movieid INT NULL,
directorid INT NULL,
dname VARCHAR (500) NULL,
addition VARCHAR (1000) NULL
)
//14 million of data
CREATE TABLE dbo.movies
(
movieid VARCHAR (20) NULL,
title VARCHAR (400) NULL,
mvyear VARCHAR (100) NULL,
actorid VARCHAR (20) NULL,
actorname VARCHAR (250) NULL,
sex CHAR (1) NULL,
as_character VARCHAR (1500) NULL,
languages VARCHAR (1500) NULL,
genres VARCHAR (100) NULL
)
And this is my new tables:
DROP TABLE actor
CREATE TABLE actor (
id INT PRIMARY KEY IDENTITY,
name VARCHAR(200) NOT NULL,
sex VARCHAR(1) NOT NULL
)
DROP TABLE actor_character
CREATE TABLE actor_character(
id INT PRIMARY KEY IDENTITY,
character VARCHAR(100)
)
DROP TABLE director
CREATE TABLE director(
id INT PRIMARY KEY IDENTITY,
name VARCHAR(200) NOT NULL,
addition VARCHAR(150)
)
DROP TABLE movie
CREATE TABLE movie(
id INT PRIMARY KEY IDENTITY,
title VARCHAR(200) NOT NULL,
year INT
)
DROP TABLE language
CREATE TABLE language(
id INT PRIMARY KEY IDENTITY,
language VARCHAR (100) NOT NULL
)
DROP TABLE genre
CREATE TABLE genre(
id INT PRIMARY KEY IDENTITY,
genre VARCHAR(100) NOT NULL
)
DROP TABLE director_movie
CREATE TABLE director_movie(
idDirector INT,
idMovie INT,
CONSTRAINT fk_director_movie_1 FOREIGN KEY (idDirector) REFERENCES director(id),
CONSTRAINT fk_director_movie_2 FOREIGN KEY (idMovie) REFERENCES movie(id),
CONSTRAINT pk_director_movie PRIMARY KEY(idDirector,idMovie)
)
DROP TABLE genre_movie
CREATE TABLE genre_movie(
idGenre INT,
idMovie INT,
CONSTRAINT fk_genre_movie_1 FOREIGN KEY (idMovie) REFERENCES movie(id),
CONSTRAINT fk_genre_movie_2 FOREIGN KEY (idGenre) REFERENCES genre(id),
CONSTRAINT pk_genre_movie PRIMARY KEY (idMovie, idGenre)
)
DROP TABLE language_movie
CREATE TABLE language_movie(
idLanguage INT,
idMovie INT,
CONSTRAINT fk_language_movie_1 FOREIGN KEY (idLanguage) REFERENCES language(id),
CONSTRAINT fk_language_movie_2 FOREIGN KEY (idMovie) REFERENCES movie(id),
CONSTRAINT pk_language_movie PRIMARY KEY (idLanguage, idMovie)
)
DROP TABLE movie_actor
CREATE TABLE movie_actor(
idMovie INT,
idActor INT,
CONSTRAINT fk_movie_actor_1 FOREIGN KEY (idMovie) REFERENCES movie(id),
CONSTRAINT fk_movie_actor_2 FOREIGN KEY (idActor) REFERENCES actor(id),
CONSTRAINT pk_movie_actor PRIMARY KEY (idMovie,idActor)
)
UPDATE:
I'm using SQL Server 2008.
Sorry guys i forgot to mention that are different databases :
The not normalized is call disciplinedb and the my normalized call imdb.
Best regards,
Valter Henrique.
If both tables are in the same database, then the most efficient transfer is to do it all within the database, preferably by sending a SQL statement to be executed there.
Any movement of data from the d/b server to somewhere else and then back to the d/b server is to be avoided unless there is a reason it can only be transformed off-server. If the destination is different server, then this is much less of an issue.
Though my tables were dwarfs compared to yours, I got over this kind of problem once with stored procedures. For MySQL, below is a simplified (and untested) essence of my script, but something similar should work with all major SQL bases.
First you should just add a new integer year column (int_year in example) and then iterate over all rows using the procedure below:
DROP PROCEDURE IF EXISTS move_data;
CREATE PROCEDURE move_data()
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE orig_id INT DEFAULT 0;
DECLARE orig_year VARCHAR DEFAULT "";
DECLARE cur1 CURSOR FOR SELECT id, year FROM table1;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
OPEN cur1;
PREPARE stmt FROM "UPDATE table1 SET int_year = ? WHERE id = ?";
read_loop: LOOP
FETCH cur1 INTO orig_id, orig_year;
IF done THEN
LEAVE read_loop;
END IF;
SET #year= orig_year;
SET #id = orig_id;
EXECUTE stmt USING #orig_year, #id;
END LOOP;
CLOSE cur1;
END;
And to start the procedure, just CALL move_data().
The above SQL has two major ideas to speed it up:
Use CURSORS to iterate over a large table
Use PREPARED statement to quickly execute pre-known commands
PS. for my case this speeded things up from ages to seconds, though in your case it can still take a considerable amount of time. So it would be probably best to execute from command line, not some web interface (e.g. PhpMyAdmin).
I just recently did this for ~150 Gb of data. I used a pair of merge statements for each table. The first merge statement said "if it's not in the destination table, copy it there" and the second said "if it's in the destination table, delete it from the source". I put both in a while loop and only did 10000 rows in each operation at a time. Keeping it on the server (and not transferring it through a client) is going to be a huge boon for performance. Give it a shot!