Arbeta med ARRAYs
Funktioner för datamanipulering i PostgreSQL
Brian Piccolo
Sr. Director, Digital Strategy
Innan vi börjar
CREATE TABLE-exempel
CREATE TABLE my_first_table (
first_column text,
second_column integer
);
INSERT-exempel
INSERT INTO my_first_table
(first_column, second_column) VALUES ('text value', 12);
ARRAY – en särskild typ
Vi skapar en enkel tabell med två arraykolumner.
CREATE TABLE grades (
student_id int,
email text[][],
test_scores int[]
);
INSERT-satser med ARRAYs
Exempel på INSERT-sats:
INSERT INTO grades
VALUES (1,
'{{"work","[email protected]"},{"other","[email protected]"}}',
'{92,85,96,88}' );
Komma åt ARRAYs
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 |
+--------+--------------------+-------------+
Observera att arrayindex i PostgreSQL börjar på ett, inte noll.
Söka i ARRAYs
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-funktioner och operatorer
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-funktioner och operatorer
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 |
+---------+---------------------+-------------+
Nu kör vi en övning!
Funktioner för datamanipulering i PostgreSQL
