How to test an SQL Update statement before running it?

Harness transaction power

Employ SQL transactions as your safety net. You can COMMIT to save any changes made during this transaction. However, if something panics your program, just ROLLBACK:

BEGIN;
-- Unleashing your powerful UPDATE
UPDATE table SET col = 'updated_value' WHERE filter;

-- Let's peek at the consequences of our actions
SELECT * FROM table WHERE condition;

-- Is it a bird, is it a plane...?
-- No, my UPDATE is correct:
COMMIT;
-- Houston, we have a problem:
ROLLBACK;


Our test run now mirrors a lab experiment: contained, controlled, and committed only if successful.

Toolbelt of testing techniques

Pen-testing with WHERE 1=0

Reveal your UPDATE's true nature without making any real changes by playing sherlock:

SELECT * FROM table WHERE 1=0;
-- Testing...
UPDATE table SET col = 'value' WHERE 1=0;


Backup and boogie

Clone your table to avert a data catastrophe (or worse, embarrassment):

-- Our table's even got a stunt double now!
CREATE TABLE table_backup AS SELECT * FROM table;


Update 'Under the Hood'

Cross-examine your soon-to-be-update's impact within the safe parameters of an uncommitted transaction:

-- How things stand pre-UPDATE
SELECT * FROM table WHERE condition;

-- The anticipated after-effects within our sacred transaction
SELECT * FROM table WHERE condition;


Mastering your transaction's journey

Control thy commit

Flip the autocommit switch off for a hand-held transaction journey:

SET autocommit = 0; -- Autocommit? Not on my watch!
-- All operations here are under your mighty control
COMMIT; -- Thanks pal, save the changes 
ROLLBACK; -- I've changed my mind, toss it


Travel Light

Keep it small, keep it simple. Just like minimal luggage for a smoother trip, less data equals less waiting and risk:

-- This transaction is on a diet
BEGIN;
-- Update just a wee bit of data
COMMIT;


Wrappers to the rescue

Invoke language wrappers, your sidekicks in controlling transaction execution right from your cozy code corner.

Double-check derby

Since we're all paranoid here, run an extra SELECT post-ROLLBACK to ensure no errant mutation in your data:

-- After performing its reversal magic, let's peek
SELECT * FROM table WHERE condition;


Visualization

Imagine your UPDATE as picking out a new wardrobe 🧥 for your data.

Current Wardrobe: [Item1 - Old-fashioned, Item2 - Decent, Item3 - Tattered]
New Fashion Goal: "Make Item3 stylish"

BEFORE:

Fitting Trial: [🔍🧥]

• It's a virtual fitting room! 😂

AFTER:

Final Makeover: [👗🧥]

• Transform your data into a fashion icon. Ooh-la-la!

Wrap it up in a fancy package with no unfortunate surprises. Dress up your data with confidence!

Complete your safety checklist

Plan, preview, and preen

Inspect the query execution plan to predict the collateral, like counting drinks before a wild party!

When FALSE is your friend

Craft safe Update statements with "WHERE FALSE", a fail-safe that feels like a parachute:

UPDATE table SET col = 'value' WHERE FALSE; -- Aha! No rows updated
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Comment control

Use line comments -- to fine-tune your SQL's execution or to prank your colleagues:

-- UPDATE table 
-- SET col1 = 'value1', -- Hello, World!
--     col2 = 'value2'  -- It's me, the harmless SQL comment 😈
-- WHERE condition;


Inspect after-effects

Post-update or post-rollback, probe your data for integrity because trust is earned, not given.