Select one or more columns of data from a table:
SELECT column_name_1, column_name_2 FROM table_name;
Select all of the columns in a table:
SELECT * FROM table_name;
Get only unique lines in a query:
SELECT DISTINCT column_name FROM table_name;
Perform calculations in a query:
SELECT column_name_1, ROUND(column_name_2 / 1000.0) FROM table_name;
Select only the data meeting certain criteria:
SELECT * FROM table_name WHERE column_name = 'Hello World';
Combine conditions:
SELECT * FROM table_name WHERE (column_name_1 >= 1000) AND (column_name_2 = 'A' OR column_name_2 = 'B');
Sort results using ASC
for ascending order or DESC
for descending order:
SELECT * FROM table_name ORDER BY column_name_1 ASC, column_name_2 DESC;
Use NULL
to represent missing data.
NULL
is neither true nor false.
Operations involving NULL
produce NULL
, e.g., 1+NULL
, 2>NULL
, and 3=NULL
are all NULL
.
Test whether a value is null:
SELECT * FROM table_name WHERE column_name IS NULL;
Test whether a value is not null:
SELECT * FROM table_name WHERE column_name IS NOT NULL;
Combine data into groups and calculate combined values in groups:
SELECT column_name_1, SUM(column_name_2), COUNT(*) FROM table_name GROUP BY column_name_1;
Join data from two tables:
SELECT * FROM table_name_1 JOIN table_name_2 ON table_name_1.column_name = table_name_2.column_name;
SQL commands must be combined in the following order:
SELECT
, FROM
, JOIN
, ON
, WHERE
, GROUP BY
, ORDER BY
.
Create tables by specifying column names and types. Include primary and foreign key relationships and other constraints.
CREATE TABLE survey(
taken INTEGER NOT NULL,
person TEXT,
quant REAL NOT NULL,
PRIMARY KEY(taken, quant),
FOREIGN KEY(person) REFERENCES person(ident)
);
Put multiple queries in a transaction to ensure they are ACID (atomic, consistent, isolated, and durable):
BEGIN TRANSACTION;
DELETE FROM table_name_1 WHERE condition;
INSERT INTO table_name_2 values(...);
END TRANSACTION;
Execute queries in a general-purpose programming language by:
Python example:
import sqlite3
connection = sqlite3.connect("database_name")
cursor = connection.cursor()
cursor.execute("...query...")
for r in cursor.fetchall():
...process result r...
cursor.close()
connection.close()