Data changes, so the best query plan changes with it. SQL was built to handle this data-dependent environment. Is one column composed of mostly one or two valu

Data changes, so the best query plan changes with it. SQL was built to handle this data-dependent environment. Is one column composed of mostly one or two values? Then an index lookup on that column is not very optimal, and the database can use something else. There is more than one type of join (INNER, LEFT OUTER, etc), and more than one join algorithm (neesed loop, merge, hash, etc). All these change based on the data. Even the join order can have a huge impact on query time, and needs to adapt based on the number of rows you'll pull from each table. A lot of SQL queries are built from templates, or built by ORMs. Optimisations are critical to turn these templates queries into something efficient. SQL can also be very expressive, a "NOT EXISTS (SELECT 1 FROM thing WHERE foobar)" could be more readable than doing a join and where clause. Though interestingly, you get a much more declarative query style with nosql databases and key-value stores. So there are alternatives out there.