Praca z typem ARRAY
Funkcje do manipulowania danymi w PostgreSQL
Brian Piccolo
Sr. Director, Digital Strategy
Zanim zaczniemy
Przykład CREATE TABLE
CREATE TABLE my_first_table (
first_column text,
second_column integer
);
Przykład INSERT
INSERT INTO my_first_table
(first_column, second_column) VALUES ('text value', 12);
ARRAY – typ specjalny
Utwórzmy prostą tabelę z dwiema kolumnami tablicowymi.
CREATE TABLE grades (
student_id int,
email text[][],
test_scores int[]
);
Instrukcja INSERT z typem ARRAY
Przykładowa instrukcja INSERT:
INSERT INTO grades
VALUES (1,
'{{"work","[email protected]"},{"other","[email protected]"}}',
'{92,85,96,88}' );
Dostęp do elementów ARRAY
SELECT
email[1][1] AS type,
email[1][2] AS address,
test_scores[1],
FROM grades;
+--------+--------------------+-------------+
| type | address | test_scores |
|--------|--------------------|-------------|
| work | [email protected] | 92 |
| work | [email protected] | 76 |
+--------+--------------------+-------------+
Indeksy tablic w PostgreSQL zaczynają się od jedynki, nie od zera.
Przeszukiwanie tablic ARRAY
SELECT
email[1][1] as type,
email[1][2] as address,
test_scores[1]
FROM grades
WHERE email[1][1] = 'work';
+--------+--------------------+-------------+
| type | address | test_scores |
|--------|--------------------|-------------|
| work | [email protected] | 92 |
| work | [email protected] | 76 |
+--------+--------------------+-------------+
Funkcje i operatory ARRAY
SELECT
email[2][1] as type,
email[2][2] as address,
test_scores[1]
FROM grades
WHERE 'other' = ANY (email);
+---------+---------------------+-------------+
| type | address | test_scores |
|---------|-----------------------------------|
| other | [email protected] | 92 |
| null | null | 76 |
+---------+---------------------+-------------+
Funkcje i operatory ARRAY
SELECT
email[2][1] as type,
email[2][2] as address,
test_scores[1]
FROM grades
WHERE email @> ARRAY['other'];
+---------+---------------------+-------------+
| type | address | test_scores |
|---------|-----------------------------------|
| other | [email protected] | 92 |
| null | null | 76 |
+---------+---------------------+-------------+
Czas na ćwiczenia!
Funkcje do manipulowania danymi w PostgreSQL
