jsdb

SQL operations written in Javascript for educational purposes.

Cool a new database! Is this a great database to use in production?

No. Don't use this for anything except learning about how SQL processes a query.

What operations are supported?

Basic implementations of the following:

SELECT
FROM
CROSS JOIN
INNER JOIN
LEFT JOIN
RIGHT JOIN
WHERE
GROUP BY
Aggregate functions: ARRAY_AGG, MAX, MIN, COUNT
DISTINCT
ORDER BY
OFFSET
LIMIT

How do I use this database?

The purpose of this database is education so the best way to "use" it is to go through the code and understand how the various operations are implemented.

If you are a Javascript programmer I suspect you will find that it is much simpler than you think. Give it a look!

OK, smart-alec, but how do I use it?

The thing to understand is that all operations in this database (and conceptually in a real database also) take tables as input and produce tables as output. So you take a table and provide it to an operation, getting a modified table back in return. To apply multiple operations, supply that modified database to the next operation.

For example, the query:

SELECT DISTINCT status, charity_group.name, COUNT(*) AS count FROM employee
    JOIN employee_charity_group ON employee_charity_group.a = employee.id
    JOIN charity_group ON charity_group.id = employee_charity_group.b
    WHERE employee.salary > 150000
    GROUP BY status, charity_group.name

Is done like this:

// First joins
let result = INNER_JOIN( employee, employee_charity_group,
  (c) => c["employee_charity_group.A"] === c["employee.id"]
);
result = INNER_JOIN( result, charity_group,
  (c) => c["employee_charity_group.B"] === c["charity_group.id"]
);

// then WHERE
result = WHERE(result, (row) => row['employee.salary'] > 150000);

// then Group By and aggregate
result = GROUP_BY(result, ['employee.status', 'charity_group.name']);
result = COUNT(result, 'charity_group.name');

// then SELECT
result = SELECT(result, ['employee.status', 'charity_group.name','COUNT(charity_group.name)'],{'COUNT(charity_group.name)': 'count'})
result = DISTINCT(result, ['employee.status', 'charity_group.name', 'count'])
table(result);

References

A good primer on SQL operation execution order: