Práce s poli (ARRAY)
Funkce pro práci s daty v PostgreSQL
Brian Piccolo
Sr. Director, Digital Strategy
Než začneme
Příklad CREATE TABLE
CREATE TABLE my_first_table (
first_column text,
second_column integer
);
Příklad INSERT
INSERT INTO my_first_table
(first_column, second_column) VALUES ('text value', 12);
ARRAY – speciální datový typ
Vytvoříme jednoduchou tabulku se dvěma sloupci typu pole.
CREATE TABLE grades (
student_id int,
email text[][],
test_scores int[]
);
Příkazy INSERT s poli (ARRAY)
Příklad příkazu INSERT:
INSERT INTO grades
VALUES (1,
'{{"work","[email protected]"},{"other","[email protected]"}}',
'{92,85,96,88}' );
Přístup k prvkům pole (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 |
+--------+--------------------+-------------+
Indexy polí v PostgreSQL začínají jedničkou, nikoli nulou.
Vyhledávání v polích (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 |
+--------+--------------------+-------------+
Funkce a operátory pro 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 |
+---------+---------------------+-------------+
Funkce a operátory pro 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 |
+---------+---------------------+-------------+
Pojďme procvičovat!
Funkce pro práci s daty v PostgreSQL
