Werken met ARRAY’s
Functies voor het manipuleren van data in PostgreSQL
Brian Piccolo
Sr. Director, Digital Strategy
Voor we beginnen
CREATE TABLE-voorbeeld
CREATE TABLE my_first_table (
first_column text,
second_column integer
);
INSERT-voorbeeld
INSERT INTO my_first_table
(first_column, second_column) VALUES ('text value', 12);
ARRAY: een speciaal type
Laten we een eenvoudige tabel maken met twee arraykolommen.
CREATE TABLE grades (
student_id int,
email text[][],
test_scores int[]
);
INSERT-statements met ARRAY’s
Voorbeeld van een INSERT-statement:
INSERT INTO grades
VALUES (1,
'{{"work","[email protected]"},{"other","[email protected]"}}',
'{92,85,96,88}' );
Toegang tot ARRAY’s
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 |
+--------+--------------------+-------------+
Let op: PostgreSQL-arrayindexen beginnen bij één, niet bij nul.
ARRAY’s doorzoeken
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 |
+--------+--------------------+-------------+
ARRAY-functies en -operators
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 |
+---------+---------------------+-------------+
ARRAY-functies en -operators
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 |
+---------+---------------------+-------------+
Laten we oefenen!
Functies voor het manipuleren van data in PostgreSQL
