59 lines
1.3 KiB
Markdown
59 lines
1.3 KiB
Markdown
---
|
|
tags: [databases, SQL, SQLite]
|
|
created: Wednesday, November 13, 2024
|
|
---
|
|
|
|
# SQLite
|
|
|
|
## Enabling foreign key constraints
|
|
|
|
Foreign key constraints are not enabled by default - it is very permissive. You
|
|
must manually turn them on, as part of the connection process:
|
|
|
|
```py
|
|
connection = sqlite3.connect("my_database.db")
|
|
connection.execute("PRAGMA foreign_keys = ON")
|
|
```
|
|
|
|
## INSERT OR IGNORE INTO
|
|
|
|
If table has a `UNIQUE` constraint on a field, insert if it is unique otherwise
|
|
skip without throwing a constraint error.
|
|
|
|
```sql
|
|
INSERT OR IGNORE INTO table_name (value) VALUES (:value)
|
|
```
|
|
|
|
## exec and fetchall
|
|
|
|
For `CREATE`, `INSERT`, `UPDATE`, `DELETE` operations it is sufficient to simply
|
|
use `execute` to carry out the operations:
|
|
|
|
```py
|
|
cursor = connection.cursor()
|
|
cursor.execute(sql)
|
|
```
|
|
|
|
For `SELECT` operations, you must add a return statement that uses `fetchall`:
|
|
|
|
```py
|
|
sql = "SELECT * FROM table"
|
|
cursor = connection.cursor()
|
|
cursor.execute(sql)
|
|
return cursor.fetchall()
|
|
```
|
|
|
|
## SELECT response data type
|
|
|
|
A `SELECT` operation returns a [list](Lists_in_Python.md) of
|
|
[tuples](Tuples_in_Python.md) where each entry in the tuple is a returned field.
|
|
|
|
For example:
|
|
|
|
```py
|
|
entries_sql = "SELECT title, size FROM entries"
|
|
|
|
entries_response = cursor.execute(entries_sql)
|
|
print(cursor.fetchall())
|
|
# [('Lorem ipsum', 127), ('Dolar sit', 4231)]
|
|
```
|