Schema Diff

Compare two database schemas and generate ALTER TABLE migration statements for added, removed, and modified columns.

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Input
Output
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About schema diff

Schema Diff is a small tool that does one job while you watch. Nothing is saved, so a reload gives you a clean start.

Load the page once and it works offline from then on. Nothing about the tool needs a connection after that first request.

You will find it under SQL & databases, alongside 27 other tools for the same sort of job.

How to use it

01
Start it
Every control is on the tool itself. Keyboard shortcuts, where there are any, are listed beside it.
02
Watch it run
It updates in the page as you go. Nothing is sent anywhere, so it keeps working with the network off.
03
Close when done
Nothing is stored between visits. Reloading gives you a clean start rather than picking up where you left off.

Examples

Schema Evolution
Compare two table schemas and generate migration SQL
Input
input1: CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(100));
input2: CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(100), email VARCHAR(255));
Output
Type: column_added
Table: users
Column: email
Detail: Column 'email' (VARCHAR(255)) was added to 'users'

Questions

Does Schema Diff work offline?+

Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.

Does it remember anything between visits?+

No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.

Is it accurate?+

Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.

Does it make a sound?+

Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.

Can I use Schema Diff on a phone?+

Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.