The Essential SQL Commands Cheat Sheet for Beginners

Query Commands

SELECT

Basic query building block to retrieve data.

SELECT *

Using * with SELECT returns all columns.

SELECT column

Specify exact columns with their name.

SELECT table.column

Reference a column from a specific table.

FROM

Specify where to find data.

AS

Temporarily alias a table name or column to a new name.

WHERE

Filter results with a condition.

AND

Use multiple conditions with a WHERE clause. Results must match all conditions.

OR

Use multiple conditions with a WHERE clause. Results only need to match one condition.

ORDER BY

Order the results by a column. The database chooses how to order.

ORDER BY column ASC

Order the results by a column in ascending order.

ORDER BY column DESC

Order the results by a column in descending order.

LIMIT

Restrict the number of results returned.

OFFSET

Skip the first OFFSET number of rows. Often used with LIMIT.

SUBQUERY

Run a query to retrieve data for another query.

Aggregate Functions¹

COUNT

Count the number of rows that match the query.

MAX

Return the highest value in a numeric column.

MIN

Return the lowest value in a numeric column.

SUM

Sum the values of a numeric column.

AVG

Calculate the average value for a numeric column.

HAVING

Used with aggregate functions instead of the WHERE clause.

GROUP BY

Used to refine an aggregate result.

Operators

LIKE

Case-sensitive search for a pattern with a wildcard operator (%).

ILIKE

Case-insensitive search for a pattern with a wildcard operator (%).

BETWEEN

Search for a value between two values. Works with dates or numbers.

>

Search for values greater than a condition.

>=

Search for values greater or equal to a condition.

<

Search for values less than a condition.

<=

Search for values less than or equal to a condition.

=

Search for values matching a condition exactly.

<>

Search for values not equal to a condition.

UNION

Combine two unique queries (with the same columns) into one result.

UNION ALL

Combine two queries (with the same columns) into one result. Duplicates allowed.

IN

Shorthand for WHERE. Specifies multiple OR conditions.

NOT IN

Shorthand for WHERE. Specifies multiple OR conditions (inverted) or not equal to.

IS NULL

Check for empty values.

IS NOT NULL

Check for no empty values.

INTERSECT

Return results which match two queries.

MINUS

Return results in one query which are not in another query.¹

Joins

ON

Used to specify the column to compare and match results.

USING

Shorthand for ON, used when the column name is the same in both tables.

LEFT OUTER JOIN

All the results from the left table, with only the matching results from the right table.

LEFT OUTER JOIN (WITH NULL)

(With null) All the results from the left table but not in the right table.

INNER JOIN

All the results that match in both the left and right tables.

FULL OUTER JOIN

All the results from both the left and right tables.

FULL OUTER JOIN (WITH NULL)

(With null) all the results from both the left and right tables excluding results in both tables.

RIGHT OUTER JOIN

All the results from the right table, with only the matching results from the left table.

RIGHT OUTER JOIN (WITH NULL)

(With null) All the results from the right table but not in the left table.

Creating and Editing Tables

CREATE TABLE

Create a new table.

NULL

Allow empty values for this field.

NOT NULL

Don't allow empty values for this field.

DEFAULT

A value to populate the field with if one is not supplied.

AS

Create a new table based on the structure of an existing table. The new table will contain the data from the old table.

ALTER TABLE (ADD COLUMN)

Add a new column to an existing table.

ALTER TABLE (DROP COLUMN)

Remove a column from an existing table.

ALTER TABLE (ALTER COLUMN)

Change the datatype of an existing column.

ALTER TABLE (RENAME COLUMN)

Rename an existing column.

ALTER TABLE (RENAME TABLE)

Rename an existing table.

ALTER TABLE (MODIFY NULL)

Allow null values for a column.

ALTER TABLE (MODIFY NOT NULL)

Prevent null values for a column.

DROP TABLE

Delete a table and all its data.

TRUNCATE TABLE

Delete all the data in a table, but not the table itself.

Constraints

PRIMARY KEY

A value that uniquely identifies a record in a table. A combination of NOT NULL and UNIQUE.

FOREIGN KEY

References a unique value in another table. Often a primary key in the other table.

UNIQUE

Enforce unique values for this column per table.

CHECK

Ensure values meet a specific condition.

INDEX (CREATE)

Optimise tables and greatly speed up queries by adding an index to a column.

INDEX (CREATE UNIQUE)

Create an index that does not allow duplicate values.

INDEX (DROP)

Remove an index.

Creating and Editing Data

INSERT (SINGLE VALUE)

Add a new record to a table.

INSERT (MULTIPLE VALUES)

Add several new records to a table.

INSERT (SELECT)

Add records to a table, but get the values from an existing table.

UPDATE (ALL)

Modify all existing records in a table.

UPDATE (WHERE)

Modify existing records in a table which match a condition.

DELETE (ALL)

Remove all records from a table.

DELETE (WHERE)

Remove records from a table which match a condition.

Creating and Editing Triggers¹

CREATE TRIGGER

Create a trigger.

CREATE TRIGGER (OR MODIFY)

Create a trigger, or update an existing trigger if one is found with the same name.

WHEN (BEFORE)

Run the trigger before the event happens.

WHEN (AFTER)

Run the trigger after the event happens.

EVENT (INSERT)

Run the trigger before or after an insert happens.

EVENT (UPDATE)

Run the trigger before or after an update happens.

EVENT (DELETE)

Run the trigger before or after a delete happens.

ON

Which table to target with this trigger.

TRIGGER_TYPE (FOR EACH ROW)

Execute the trigger for every row changed.

TRIGGER_TYPE (FOR EACH STATEMENT)

Execute the trigger once per SQL statement, regardless of how many rows are altered.

EXECUTE

Keyword to indicate the end of the main trigger definition.

DROP TRIGGER

Delete a trigger.

Creating and Editing Views

CREATE VIEW

Create a new view.

AS

Define where to retrieve the data for a view.

WITH CASCADED CHECK OPTION

Ensure any data modified through a view meets the rules defined by the rule. Apply this to any other views.

WITH LOCAL CHECK OPTION

Ensure any data modified through a view meets the rules defined by the rule. Ignore this for any other views.

CREATE RECURSIVE VIEW

Create a recursive view (one that refers to a recursive common table expression).

CREATE TEMPORARY VIEW

Create a view that exists for the current session only.

DROP VIEW

Delete a view.

Common Table Expressions (CTEs)¹

WITH

Create a new common table expression.

AS

Specify the data to use in the CTE.

, (COMMA)

Chain multiple CTEs.

¹Database engine implementations and support often vary.