ソフトウェアエンジニアの技術ブログ：Software engineer tech blog

create table person (
	id int,
	first_name varchar(50),
	last_name varchar(50),
	gender varchar(7),
	birth_day date
);

testdb=# \d person
Table “public.person”
Column | Type | Collation | Nullable | Default
————+———————–+———–+———-+———
id | integer | | |
first_name | character varying(50) | | |
last_name | character varying(50) | | |
gender | character varying(7) | | |
birth_day | date | | |

### テーブルに制約をつける

create table person (
	id BIGSERIAL not null primary key,
	first_name varchar(50) not null,
	last_name varchar(50) not null,
	gender varchar(7) not null,
	birth_day date not null,
	email varchar(150)
);

bigserial 整数を自動決定
primary key キーとして扱う
not null 空白を許可しない

### テーブルにデータを挿入

insert into person (
	first_name,
	last_name,
	gender,
	birth_day
) values ('Anne', 'Smith', 'Femail', DATE '1988-01-09');

insert into person (
	first_name,
	last_name,
	gender,
	birth_day,
	email
) values ('Jake', 'Jone', 'Male', DATE '1990-01-10', 'jake@gmail.com');

testdb=# select * from person;
id | first_name | last_name | gender | birth_day | email
—-+————+———–+——–+————+—————-
1 | Anne | Smith | Femail | 1988-01-09 |
2 | Jake | Jone | Male | 1990-01-10 | jake@gmail.com
(2 rows)

データの自動生成
https://mockaroo.com/

create table person (
	id BIGSERIAL not null primary key,
	first_name varchar(50) not null,
	last_name varchar(50) not null,
	gender varchar(7) not null,
	email varchar(150),
	date_of_birth date not null,
	country varchar(50) not null
);

$ \i /home/vagrant/dev/app/person.sql
$ select * from person;

create table person (
	id BIGSERIAL not null primary key,
	first_name varchar(50) not null,
	last_name varchar(50) not null,
	gender varchar(7) not null,
	email varchar(150),
	date_of_birth date not null,
	country varchar(50) not null,
	car_id BIGINT REFERENCES car (id),
	unique(car_id)
);

create table car (
	id BIGSERIAL not null primary key,
	make varchar(50) not null,
	model varchar(50) not null,
	price varchar(50) not null
);

BIGINT REFERENCESで関連づけるのか。なるほど、勉強になるね。

テーブルを作成
$ CREATE TABLE test(image bytea);

bytea型はバイナリデータを保存。1Gまで可能
https://www.postgresql.jp/document/9.6/html/datatype-binary.html

画像データの登録

$dsn = "pgsql:dbname=testdb host=localhost port=5432";
$user = "user1";
$password = "password";

try {
	$dbh = new PDO($dsn, $user, $password);
	print('connection success<br>');

	$stmt = $dbh->prepare("insert into test (image) values (:image)");

	$fp = fopen("images.jpeg", "rb");
	$stmt->bindParam(':image', $fp, PDO::PARAM_LOB);
	$stmt->execute();

} catch(PDOException $e){
	print("Error:".$e->getMessage());
	die();
}

画像の表示

$dsn = "pgsql:dbname=testdb host=localhost port=5432";
$user = "user1";
$password = "password";

try {
	$dbh = new PDO($dsn, $user, $password);

	$stmt = $dbh->prepare("select image from test");
	$stmt->execute();
	$stmt->bindColumn("image", $image, PDO::PARAM_LOB);
	$stmt->fetch();
	header("Content-Type: image/jpeg");
	fpassthru($image);

	unset($db);
} catch(PDOException $e){
	print("Error:".$e->getMessage());
	die();
}

なるほど、DBに画像保存も可能なのね。
データサイズが気になるが、軽量な画像であれば良さそう

PostgreSQLは削除フラグがついて見えなくなっているだけのため、削除データを定期的にきれいにする必要があり、この処理をVACUUMという。

$ psql –version
psql (PostgreSQL) 14.2 (Ubuntu 14.2-1.pgdg20.04+1)
$ sudo -u postgres psql
psql (14.2 (Ubuntu 14.2-1.pgdg20.04+1))
Type “help” for help.

postgres=# \l
postgres=# \c testdb;
testdb=# \d department;
testdb=# select * from department;

testdb=# delete from department where department_code = ‘c’;
testdb=# vacuum verbose department;
INFO: vacuuming “public.department”
INFO: scanned index “pk_department” to remove 1 row versions
DETAIL: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s
INFO: table “department”: removed 1 dead item identifiers in 1 pages
DETAIL: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s
INFO: index “pk_department” now contains 5 row versions in 2 pages
DETAIL: 1 index row versions were removed.
0 index pages were newly deleted.
0 index pages are currently deleted, of which 0 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO: table “department”: found 1 removable, 5 nonremovable row versions in 1 out of 1 pages
DETAIL: 0 dead row versions cannot be removed yet, oldest xmin: 747
Skipped 0 pages due to buffer pins, 0 frozen pages.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
VACUUM

vacuum ${table_name} でテーブルをvacuumできる。
なるほど。

autovacuumの設定はpostgres.confで設定されている。