Converting MM/DD/YYYY HH:MM:SS AM/PM to ISO 8601 in SQLite

Parsing Non-Standard Date-Time Formats With AM/PM Notation

Structural Analysis of DateTime Conversion Requirements

The core challenge involves transforming date-time values from a custom string format containing mixed-case AM/PM notation into ISO 8601-compliant timestamps. The source data exhibits several problematic characteristics:

Month-first date format: Strings use MM/DD/YYYY ordering instead of SQLite’s preferred YYYY-MM-DD
12-hour time notation: Hours range from 1-12 with AM/PM suffixes rather than 00-23
Variable-length components: Single-digit months/days/hours lack leading zeros
Composite delimiter usage: Commas separate date and time portions while slashes and colons divide components
Case-sensitive period markers: AM/PM designators appear in uppercase but must be case-insensitively handled

These characteristics prevent direct use of SQLite’s built-in date/time functions, requiring multi-stage parsing operations. The transformation must account for edge cases including:

12:00:00 AM → 00:00:00 (midnight rollover)
12:00:00 PM → 12:00:00 (noon preservation)
Hour values between 1-11 PM requiring +12 conversion
Mixed 12-hour/24-hour format detection
Invalid datetime prevention through range validation

Critical Failure Points in DateTime Conversion Logic

Common pitfalls when handling this conversion include:

1. AM/PM Hour Calculation Errors

Adding 12 hours to all PM times converts 12:45 PM → 24:45 (invalid)
Failing to subtract 12 hours from 12:XX AM creates 12:XX instead of 00:XX
Incorrect handling of 24-hour format times with superfluous PM markers

2. Component Extraction Flaws

Using fixed-position substring operations on variable-length dates:
- "4/7/2022" vs "12/11/2022" creates misaligned splits
Improper delimiter handling causing month/day transposition
Losing milliseconds/fractions when not present in source

3. Type Casting Issues

String-to-integer conversion failures from leftover delimiters
JSON array indexing errors due to incorrect element positions
Implicit text/numeric conversions causing comparison faults

4. Timezone Assumptions

Assuming UTC without offset markers (Z suffix)
Local timezone contamination during conversion
Daylight saving time boundary miscalculations

5. Leap Year/Date Validation Gaps

Allowing February 29 in non-leap years
Permitting month values >12 or day values >31
Ignoring 30-day month overflow

Comprehensive Conversion Methodology With Edge Case Handling

Phase 1: Input Normalization
Standardize the input format before parsing:

-- Convert to uppercase and remove spaces around commas
UPDATE teacher_temp 
SET jointime = UPPER(REPLACE(jointime, ', ', ','));

-- Handle 24-hour times with erroneous PM markers
UPDATE teacher_temp
SET jointime = REPLACE(jointime, ':PM', '') 
WHERE jointime LIKE '%:[0-9][0-9]:[0-9][0-9]PM';

Phase 2: Component Extraction
Use recursive CTE for robust parsing:

WITH RECURSIVE split(datetime, component, rest) AS (
  SELECT 
    jointime,
    '',
    REPLACE(REPLACE(REPLACE(jointime, '/', ' '), ':', ' '), ',', ' ') || ' '
  FROM teacher_temp
  UNION ALL
  SELECT 
    datetime,
    substr(rest, 1, instr(rest, ' ')-1),
    substr(rest, instr(rest, ' ')+1)
  FROM split 
  WHERE rest != ''
)
SELECT * FROM split WHERE component != '';

Phase 3: Structured Data Assembly
Map components to datetime parts using window functions:

CREATE TABLE datetime_parts AS
SELECT 
  datetime,
  MAX(CASE WHEN pos=1 THEN component END) AS month,
  MAX(CASE WHEN pos=2 THEN component END) AS day,
  MAX(CASE WHEN pos=3 THEN component END) AS year,
  MAX(CASE WHEN pos=4 THEN component END) AS hour,
  MAX(CASE WHEN pos=5 THEN component END) AS minute,
  MAX(CASE WHEN pos=6 THEN component END) AS second,
  MAX(CASE WHEN pos=7 THEN component END) AS period
FROM (
  SELECT *, ROW_NUMBER() OVER (PARTITION BY datetime) AS pos
  FROM split
) GROUP BY datetime;

Phase 4: 24-Hour Time Conversion
Implement military time conversion rules:

UPDATE datetime_parts
SET hour = 
  CASE 
    WHEN period = 'PM' AND hour < 12 THEN hour + 12
    WHEN period = 'AM' AND hour = 12 THEN 0
    ELSE hour
  END;

Phase 5: ISO 8601 Format Construction
Assemble validated components with error checking:

INSERT INTO teacher(jointime_iso)
SELECT 
  CASE WHEN
    year BETWEEN 1900 AND 2100 AND
    month BETWEEN 1 AND 12 AND
    day BETWEEN 1 AND 
      CASE month
        WHEN 2 THEN 
          CASE 
            WHEN (year % 4 = 0 AND year % 100 != 0) OR year % 400 = 0 THEN 29
            ELSE 28
          END
        WHEN 4 THEN 30
        WHEN 6 THEN 30
        WHEN 9 THEN 30
        WHEN 11 THEN 30
        ELSE 31
      END AND
    hour BETWEEN 0 AND 23 AND
    minute BETWEEN 0 AND 59 AND
    second BETWEEN 0 AND 59
  THEN
    printf('%04d-%02d-%02dT%02d:%02d:%02dZ',
      year, month, day, hour, minute, second)
  ELSE
    NULL
  END
FROM datetime_parts;

Phase 6: Validation and Error Reporting
Identify conversion failures:

-- Find invalid source records
SELECT t.* 
FROM teacher_temp t
LEFT JOIN teacher ON t.rowid = teacher.rowid
WHERE teacher.jointime_iso IS NULL;

-- Detailed error diagnostics
SELECT 
  datetime,
  CASE
    WHEN year NOT BETWEEN 1900 AND 2100 THEN 'Invalid year'
    WHEN month NOT BETWEEN 1 AND 12 THEN 'Invalid month' 
    WHEN day > 
      CASE month
        /* ... same day check logic ... */
      END THEN 'Invalid day for month'
    /* ... other component checks ... */
  END AS error
FROM datetime_parts
WHERE printf(...) IS NULL;

Alternative Approach Using JSON Functions
For environments supporting JSON1 extension:

INSERT INTO teacher(jointime_iso)
SELECT 
  strftime('%Y-%m-%dT%H:%M:%SZ',
    printf('%s-%02d-%02d %02d:%02d:%02d',
      json_extract(jparts, '$[2]'),
      json_extract(jparts, '$[0]'),
      json_extract(jparts, '$[1]'),
      CASE 
        WHEN json_extract(jparts, '$[6]') = 12 AND 
             json_extract(jparts, '$[3]') >= 12 THEN json_extract(jparts, '$[3]')
        WHEN json_extract(jparts, '$[6]') = 0 AND 
             json_extract(jparts, '$[3]') = 12 THEN 0
        ELSE json_extract(jparts, '$[3]') + json_extract(jparts, '$[6]')
      END,
      json_extract(jparts, '$[4]'),
      json_extract(jparts, '$[5]')
    )
  )
FROM (
  SELECT 
    jointime,
    json_insert(
      json_insert(
        json_replace(
          json_replace(
            json_replace(
              json('[]'),
              '$[0]', substr(jointime, 1, instr(jointime, '/')-1),
              '$[1]', substr(
                substr(jointime, instr(jointime, '/')+1),
                1, 
                instr(substr(jointime, instr(jointime, '/')+1), '/')-1
              ),
              '$[2]', substr(
                jointime,
                instr(jointime, '/') + 
                instr(substr(jointime, instr(jointime, '/')+1), '/') + 1,
                4
              )
            ),
            '$[3]', substr(
              substr(jointime, instr(jointime, ',')+2),
              1,
              instr(substr(jointime, instr(jointime, ',')+2), ':')-1
            )
          ),
          '$[4]', substr(
            substr(jointime, instr(jointime, ',')+2),
            instr(substr(jointime, instr(jointime, ',')+2), ':')+1,
            2
          ),
          '$[5]', substr(
            substr(jointime, instr(jointime, ',')+2),
            instr(substr(jointime, instr(jointime, ',')+2), ' ')+1,
            2
          )
        ),
        '$[6]', CASE 
          WHEN jointime LIKE '%PM' THEN 12 
          ELSE 0 
        END
      )
    ) AS jparts
  FROM teacher_temp
);

Performance Optimization Techniques

Precomputed Component Extraction

CREATE TABLE temp.conversion_cache AS
SELECT 
  rowid,
  substr(...) AS month,
  substr(...) AS day,
  /* ... other components ... */
FROM teacher_temp;
CREATE INDEX idx_temp_conversion ON conversion_cache(rowid);

Batch Processing With Window Functions

INSERT INTO teacher(jointime_iso)
SELECT iso FROM (
  SELECT rowid,
    CASE WHEN valid THEN printf(...) END AS iso,
    ROW_NUMBER() OVER (ORDER BY rowid) AS batch
  FROM conversion_cache
) WHERE batch BETWEEN ?1 AND ?2;

Parallel Processing Using ATTACH

ATTACH DATABASE 'source.db' AS src;
ATTACH DATABASE 'temp.db' AS tmp;
INSERT INTO tmp.conversion_cache 
SELECT * FROM src.teacher_temp;

Data Validation Framework
Implement constraint checking:

-- Create validation table
CREATE TABLE conversion_errors (
  rowid INTEGER PRIMARY KEY,
  original_text TEXT,
  error_code INT,
  error_message TEXT
);

-- Populate error tracking
INSERT INTO conversion_errors
SELECT 
  t.rowid,
  t.jointime,
  CASE
    WHEN dp.month IS NULL THEN 101
    WHEN dp.day IS NULL THEN 102
    /* ... other error codes ... */
  END,
  CASE
    WHEN dp.month IS NULL THEN 'Missing month component'
    /* ... other messages ... */
  END
FROM teacher_temp t
LEFT JOIN datetime_parts dp ON t.rowid = dp.rowid
WHERE dp.rowid IS NULL;

Alternative Timezone Handling
For UTC conversion with offset awareness:

UPDATE datetime_parts
SET tz_offset = 
  CASE 
    WHEN datetime LIKE '%+%' THEN substr(datetime, instr(datetime, '+'))
    WHEN datetime LIKE '%-%' THEN substr(datetime, instr(datetime, '-'))
    ELSE '+00:00'
  END;

INSERT INTO teacher(jointime_iso)
SELECT 
  strftime('%Y-%m-%dT%H:%M:%S', 
    printf('%04d-%02d-%02d %02d:%02d:%02d',
      year, month, day, hour, minute, second
    ),
    tz_offset
  )
FROM datetime_parts;

Legacy System Compatibility Layer
For SQLite versions <3.38 without JSON1:

CREATE TEMP TRIGGER convert_dates AFTER INSERT ON teacher_temp
BEGIN
  INSERT INTO teacher(jointime_iso)
  VALUES (
    CASE 
      WHEN (NEW.jointime LIKE '%PM' AND CAST(substr(...) AS INT) < 12)
        THEN CAST(substr(...) AS INT) + 12
      /* ... other conversion logic ... */
    END
  );
END;

Continuous Integration Testing Framework
Sample test cases:

INSERT INTO test_cases (input, expected) VALUES
  ('4/17/2022, 5:03:31 PM', '2022-04-17T17:03:31Z'),
  ('12/31/2023, 11:59:59 PM', '2023-12-31T23:59:59Z'),
  ('2/29/2024, 12:00:00 AM', '2024-02-29T00:00:00Z'), -- Leap day
  ('13/01/2025, 08:00:00 AM', NULL), -- Invalid month
  ('00/15/2026, 10:00:00 AM', NULL); -- Invalid month

SELECT 
  input,
  expected,
  (SELECT jointime_iso FROM teacher WHERE rowid = t.rowid) AS actual,
  CASE 
    WHEN (SELECT jointime_iso FROM teacher WHERE rowid = t.rowid) = expected 
    THEN 'PASS' 
    ELSE 'FAIL' 
  END AS result
FROM test_cases t;

Migration Strategy For Large Datasets

Chunked Processing

BEGIN TRANSACTION;
INSERT INTO teacher(jointime_iso)
SELECT conversion_logic FROM teacher_temp
WHERE rowid BETWEEN 1 AND 100000;
COMMIT;

Progress Tracking

CREATE TABLE conversion_progress (
  chunk_start INT,
  chunk_end INT,
  processed_at DATETIME
);

Resume Capability

SELECT MAX(chunk_end) FROM conversion_progress;

Rollback Procedure

DELETE FROM teacher WHERE rowid IN (
  SELECT rowid FROM teacher_temp
);

Final Production-Grade Solution
Combining all components:

PRAGMA journal_mode = WAL;
PRAGMA synchronous = NORMAL;

CREATE TEMP TABLE temp.conversion_context (
  rowid INTEGER PRIMARY KEY,
  month INT,
  day INT,
  year INT,
  hour INT,
  minute INT,
  second INT,
  period TEXT
);

WITH normalized AS (
  SELECT 
    rowid,
    UPPER(REPLACE(jointime, ', ', ',')) AS jointime
  FROM teacher_temp
),
components AS (
  SELECT
    rowid,
    CAST(substr(jointime, 1, instr(jointime, '/')-1) AS INT) AS month,
    CAST(substr(
      substr(jointime, instr(jointime, '/')+1),
      1,
      instr(substr(jointime, instr(jointime, '/')+1), '/')-1
    ) AS INT) AS day,
    CAST(substr(
      jointime,
      instr(jointime, '/') + 
      instr(substr(jointime, instr(jointime, '/')+1), '/') + 1,
      4
    ) AS INT) AS year,
    CAST(substr(
      substr(jointime, instr(jointime, ',')+2),
      1,
      instr(substr(jointime, instr(jointime, ',')+2), ':')-1
    ) AS INT) AS hour,
    CAST(substr(
      substr(jointime, instr(jointime, ',')+2),
      instr(substr(jointime, instr(jointime, ',')+2), ':')+1,
      2
    ) AS INT) AS minute,
    CAST(substr(
      substr(jointime, instr(jointime, ',')+2),
      instr(substr(jointime, instr(jointime, ',')+2), ' ')+1,
      2
    ) AS INT) AS second,
    CASE 
      WHEN jointime LIKE '%PM' THEN 'PM'
      ELSE 'AM'
    END AS period
  FROM normalized
)
INSERT INTO temp.conversion_context
SELECT * FROM components;

UPDATE temp.conversion_context
SET hour = 
  CASE 
    WHEN period = 'PM' AND hour < 12 THEN hour + 12
    WHEN period = 'AM' AND hour = 12 THEN 0
    ELSE hour
  END;

INSERT INTO teacher(jointime_iso)
SELECT 
  printf('%04d-%02d-%02dT%02d:%02d:%02dZ',
    year,
    month,
    day,
    hour,
    minute,
    second)
FROM temp.conversion_context
WHERE 
  year BETWEEN 1900 AND 2100 AND
  month BETWEEN 1 AND 12 AND
  day BETWEEN 1 AND 
    CASE month
      WHEN 2 THEN 
        CASE 
          WHEN (year % 4 = 0 AND year % 100 != 0) OR year % 400 = 0 THEN 29
          ELSE 28
        END
      WHEN 4 THEN 30
      WHEN 6 THEN 30
      WHEN 9 THEN 30
      WHEN 11 THEN 30
      ELSE 31
    END AND
  hour BETWEEN 0 AND 23 AND
  minute BETWEEN 0 AND 59 AND
  second BETWEEN 0 AND 59;

This comprehensive approach ensures robust conversion of non-standard datetime formats while maintaining data integrity, performance efficiency, and error traceability throughout the transformation process.

Converting MM/DD/YYYY HH:MM:SS AM/PM to ISO 8601 in SQLite

Parsing Non-Standard Date-Time Formats With AM/PM Notation

Structural Analysis of DateTime Conversion Requirements

Critical Failure Points in DateTime Conversion Logic

Comprehensive Conversion Methodology With Edge Case Handling

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Parsing Non-Standard Date-Time Formats With AM/PM Notation

Structural Analysis of DateTime Conversion Requirements

Critical Failure Points in DateTime Conversion Logic

Comprehensive Conversion Methodology With Edge Case Handling

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