SQL Cheat Sheet

SQL Cheat Sheet

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Basic query

SELECT column_names
FROM table_name;

• selects only the specified columns from a table.

SELECT *
FROM table_name;

• select all of the columns in a table.

SELECT DINSTINCT column_name
FROM table_name;

• selects only the unique values from a table.

SELECT column_names
FROM table_name
WHERE column_name operator value;

• selects only the data that meets certain criteria.
• you can use operators =,<,>, etc
• you can also combine tests using AND, OR in the WHERE clause.

SELECT column_names
FROM table_name
WHERE column_name IN (value1, value2, value3);

• selects only the data where column_name equals to value1, value2, and so on.

SELECT column_names
FROM table_name
ORDER BY column_name ASC;

• selects only the specified columns from a table, sort the results by a column in ASC (ascending) or DESC (descending) order.

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Aggregation

SELECT aggregate_function(column_name)
FROM table_name;

• Aggregate results by grouping records based on value and calculating combined values in groups.
• E.g. SELECT COUNT(*) FROM table_name will display the total number of records.
• You can use aggregate functions COUNT, SUM, MAX, MIN, AVG.

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;

• GROUP BY tells SQL what field or fields we want to use to aggregate the data. If we want to group by multiple fields, we give GROUP BY a comma separated list.

SELECT column_name, aggregate_function(column_name)
FROM table_name
GROUP BY column_name
HAVING aggregate_function(column_name) operator value;

• The HAVING keyword works exactly like the WHERE keyword, but uses aggregate functions instead of database fields.

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Joins and aliases

SELECT column_names
FROM table_name1
JOIN table_name2
ON table_name1.column_name = table_name2.column_name;

• Combine data from two tables where the values of column_name in the two tables are the same.
• Instead of ON, you can use the USING keyword as a shorthand. E.g. USING (coolumn_name).

SELECT alias1.column_name1, alias1.column_name2, alias2.column_name3
FROM table_name1 AS alias1
JOIN table_name2 AS alias2
ON alias1.column_name = alias2.column_name;

• we can use aliases to assign new names to things in the query.
• we can use as to rename column names too. E.g. SELECT journal_title AS journal.

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Saving queries

CREATE VIEW viewname AS
SELECT column_names
FROM table_name;

• create a stored query or virtual table in database for repeated queries

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Commenting

-- Select all columns
SELECT *
-- From the table_name
FROM table_name

• we can create comments in SQL queries to help us/others understand the query better

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Operators

Arithmetic operators + - * /

Comparison operators = < > <= >= <>

Logical operators ALL AND ANY BETWEEN EXISTS IN LIKE NOT OR SOME