Why does this SQLite query select all dates, even those outside of the criteria?

Designing date-compatible queries

SQLite carries out comparisons by treating dates as text, real, or integer data. Therefore, to achieve accurate results, maintain consistency between the date format used in your database and the queries. The gold standard: ISO-8601 ('YYYY-MM-DD') format.

To convert dates into the desired format, employ strftime function:

-- Transforming Cinderella 👗👠 
SELECT * FROM your_table 
WHERE strftime('%Y-%m-%d', your_date_column) BETWEEN '2023-01-01' AND '2023-01-31';


Precision in filtering ranges is achieved by converting dates to the correct format using 'date()' or 'julianday()' functions if your dates appear in diverse formats or as text.

Tackling diverse date formats

When the YYYY-MM-DD format is not in vogue in your database, tune-up your query to match the stored format instead.

Deploy substr for surgical alterations:

-- 🗡️ All hail the mighty substr, the surgeon of strings!
SELECT * FROM your_table 
WHERE substr(your_date_column, 7, 4) || '-' || 
      substr(your_date_column, 1, 2) || '-' || 
      substr(your_date_column, 4, 2) BETWEEN '2023-01-01' AND '2023-01-31';


This code reassembles a MM-DD-YYYY date into a compliant YYYY-MM-DD format, ensuring accurate comparison.

Harnessing date functions for improved accuracy

SQLite's date functions can offer soup-up accuracy and flexibility.

Deploy julianday() for precise ranges:

-- It's like dating, but in Julian! 😉
SELECT * FROM your_table 
WHERE julianday(your_date_column) BETWEEN julianday('2023-01-01') AND julianday('2023-01-31');


Julian day numbers equalize all dates, streamlining date range comparisons.

Now utilising now for current dates:

-- It's always ⏰ for now!
SELECT * FROM your_table 
WHERE your_date_column >= date('now', '-7 days');


The date('now') function gets you a regex on the current date/time—handy for dynamic date comparisons.

Common pitfalls and averts

Incorrect filtering could arise from separate date part checks, intermingling date types, or neglecting time zone offsets when they matter.

Remedies:

• Avoid dichotomizing date parts (e.g., year, month, day) for comparison unless needed.
• Stay vigilant with time zones; SQLite's time-zone-naïve.
• Consider a UTC timestamp to steer clear of time zone chaos.

Выisualisation

Let's illustrate the issue with the SQLite query not optimally filtering dates:

Calendar View: 📅
Selected Dates Criteria: [10, 11, 12] (July)

But the query returns:

🗓️ Dates Retrieved: [5, 6, 10, 11, 12, 18, 19]

Like a misbehaving bouncer:

📅┌─────┐ 🚪 Bouncer, you had ONE job!
  │ 5, 6│
  │10,11│ 👌 The chosen ones!
  │12,18│ 
  │ 19 │ 
└─────┘

Undesirable entries into our dataset depict unexpected party crashers.

Leverage SQLite for strategic querying

Tweaking date queries boosts efficiency and precision:

• Opt for indexes on date columns to turbocharge searches.
• Pre-compute frequent date ranges to minimize table scans & go fast.
• Test run queries with multiple date formats in dev to pre-emptively nix any troublemakers.
• Review your data import routines to pull off uniformity in database dates.

Following these strategies makes your SQLite queries bullet-proof.