Sql: BETWEEN vs <= and >=

The nitty-gritty

While BETWEEN and >= together with <= might seem interchangeable at first, there are nuances to consider. For instance, dealing with dates can be a potential minefield.

Dealing with time

When using BETWEEN with dates, it includes up to the last fraction of the end date's time part. This might lead to unexpected results unless handled judiciously:

-- Impractical use with time 
SELECT * FROM events WHERE event_date BETWEEN '2021-01-01' AND '2021-12-31';  -- Whoops! Midnight Cinderella?

-- More precise time control
SELECT * FROM events WHERE event_date >= '2021-01-01' AND event_date < '2022-01-01';  --Buh-bye 2021, Hello 2022!
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This shows the advantage of using half-open ranges (>= and <) to effectively handle time parts in date ranges.

Order in the court

Incorrect ordering in <= and >= can result in unexpected outcomes. Ensuring the range markers are logically set prevents such anomalies.

Clarity vs precision

While BETWEEN is a reader's delight for brevity, >= and <= offers precision, albeit verbosely. The choice largely hinges on readability preference and context.

Check your docs

Behaviour of the BETWEEN keyword might have variations across RDBMS platforms. Consult your database's documentation to navigate platform-specific variations adroitly.

Surprises and gotchas

Certain edge cases might produce different results with BETWEEN and >= and <=. Knowledge of these comes quite handy.

Inclusive vs. exclusive

BETWEEN is always inclusive. If you need to exclude the upper limit:

-- BETWEEN being inclusive
SELECT * FROM sales WHERE amount BETWEEN 100 AND 500;

-- Exclusive with >= and <
SELECT * FROM sales WHERE amount >= 100 AND amount < 500;    -- 500 kicked out!
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Fractions of time

Time fractions in timestamps can mess up things with BETWEEN. Stick with half-open ranges to stay clear:

-- Problem with BETWEEN and timestamps
SELECT * FROM logs WHERE created_at BETWEEN '2021-01-01' AND '2021-01-02';

-- Safer alternative
SELECT * FROM logs WHERE created_at >= '2021-01-01' AND created_at < '2021-01-03';   -- Time's on my side
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Mistakes to watch out for

When crafting SQL queries, keep an eye out for typical mistakes that can distort your results or degrade performance.

Not optimizing for indexes

While BETWEEN can be index-friendly, it's not guaranteed that it's treated same as >= AND <= by database optimizers resulting in performance hiccups otherwise.

Ignoring conventions

Follow your team's coding conventions. It aids maintainability and keeps your code from sticking out like a sore thumb.

Not handling NULLs

BETWEEN and >= AND <= ignore NULL values. Explicitly handle NULLs, if your logic demands it:

-- Handling a NULL, brilliantly!
SELECT * FROM table WHERE (column BETWEEN 10 AND 20) OR column IS NULL;    -- NULL-pointer exception, not today!
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Losing precision on casting

Using BETWEEN with casted columns might rob away time details i.e. CAST(column AS DATE). Always consider data type and precision.