In SQL, is UPDATE always faster than DELETE+INSERT?
In the SQL world, asking whether **UPDATE** or **DELETE+INSERT** is faster is akin to asking whether π’ or π will win the race. In most cases, **UPDATE** plays the role of the steady turtle, dealing with minor changes efficiently and swiftly, since it modifies data in place. However, in scenarios involving substantial row modifications, **DELETE+INSERT** races ahead like the hare, leveraging its agility to deal with how databases handle updates on the fly.
Consider:
- **UPDATE**: Similar to editing an existing document, making it efficient for minor tweaks, but not a fun weekend.
- **DELETE+INSERT**: Is like recreating a document for major overhauls - more effort but hey, who doesn't love a fresh start!
```sql
-- I'm in no hurry. Let's just UPDATE
UPDATE table_name SET column = new_value WHERE condition; -- Turtle Power!
-- New year, new me? Let's DELETE & INSERT!
DELETE FROM table_name WHERE condition;
INSERT INTO table_name (columns...) VALUES (values...); -- Fresh Start Activated!
Just remember, your mileage may vary, so measure those SQL miles with real data and database workload for the best pit stop choice.
Considering the choice: UPDATE vs DELETE+INSERT
Delete and Insert with large tables - think twice!
As tables grow, the cost of DELETE and INSERT also grow, like your responsibilities as an adult. This can make UPDATE (quick in-and-out) more favorable than DELETE+INSERT (whole process).
Mass updates - rebuild or retouch?
If you're dealing with numerous rows requiring changes, you might be better off rebuilding the table with Create Table As Select (CTAS), much like renovating a house when too many repairs are needed. It's a fresh start!
Primary Keys and your data's integrity
With UPDATE, primary key values remain stable, like your best friend always being there for you. On the other hand, DELETE+INSERT changes them, which might not be the best for maintaining relationships (pun intended!)
Replicated databases - An Update affair
In replicated databases, UPDATE statements are typically less gossipy and cause fewer dramas, compared to DELETE+INSERT pairs. So, keep it simple!
Challenges and solutions in UPDATE vs DELETE+INSERT scenarios
Handling unique keys and row spaces
Updating unique keys or rows without enough space can be like arranging furniture in a tiny apartment - it slows down the UPDATE operation. A strategic furniture (schema) placement can save the day!
The balanced approach
The INSERT INTO ... ON DUPLICATE KEY UPDATE command may be the sweet spot over traditional UPDATE or DELETE+INSERT. This command is like an all-you-can-eat SQL buffet, offering both efficiency and all-encompassing impact.
Looking under the SQL hood
It pays to understand how your database's engine runs, just like with your car. How it handles UNDO logging and index rebuilding can greatly impact your database's performance and hence the UPDATE or DELETE+INSERT decision.
History matters
For preserving historical data or maintaining audit trails, UPDATE operations are cleaner, leaving a traceable path (like breadcrumbs), unlike DELETE+INSERT, that freshens everything up (including history).
Performance testing
Always test before you commit, be it in life or SQL operations. Use performance testing tools like JMeter to simulate your real workload. Doing so may reveal that UPDATE operations are roughly 3 times faster than DELETE+INSERT. Who would've thought?
Watch out for fragmentation
When deciding between UPDATE and DELETE+INSERT, consider whether table fragmentation might affect your decision. Choose wisely, or you may end up with a messy room (aka fragmented table) that's hard to tidy up.
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