Why date handling matters in PostgreSQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the current date in PostgreSQL.

PostgreSQL

SELECT [1];

Drag options to blanks, or click blank then click option'

ACURRENT_DATE

BSYSDATE

CGETDATE()

DNOW()

Attempts:

3 left

💡 Hint

Common Mistakes

Using NOW() returns date and time, not just the date.

GETDATE() and SYSDATE are not PostgreSQL functions.

In PostgreSQL, CURRENT_DATE returns the current date without time.

2fill in blank

medium

Complete the code to extract the year from a date column named 'order_date'.

PostgreSQL

SELECT EXTRACT([1] FROM order_date) AS year FROM orders;

Drag options to blanks, or click blank then click option'

Amonth

Byear

Cday

Dhour

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'month' or 'day' extracts wrong parts of the date.

Using 'hour' extracts time, not date.

The EXTRACT function with year extracts the year part from a date.

3fill in blank

hard

Fix the error in the code to add 7 days to the current date.

PostgreSQL

SELECT CURRENT_DATE + [1];

Drag options to blanks, or click blank then click option'

A'7 days'

B7

CINTERVAL '7 days'

DDATE '7'

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a plain number to a date causes an error.

Using a string without INTERVAL keyword is invalid.

In PostgreSQL, to add days to a date, you add an INTERVAL value like INTERVAL '7 days'.

4fill in blank

hard

Fill both blanks to convert a text '2024-06-15' to a date and then extract the month.

PostgreSQL

SELECT EXTRACT([1] FROM [2]('2024-06-15')) AS month;

Drag options to blanks, or click blank then click option'

Amonth

Byear

Cday

D::date

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'year' or 'day' instead of 'month' in EXTRACT.

Not casting the text to date before extracting.

Use EXTRACT(month FROM ...) to get the month, and cast to ::date to convert text to date.

5fill in blank

hard

Fill all three blanks to calculate the difference in days between two dates '2024-06-20' and '2024-06-15'.

PostgreSQL

SELECT ([1]('2024-06-20') - [2]('2024-06-15')) [3] '1 day' AS days_diff;

Drag options to blanks, or click blank then click option'

ADATE

C::interval

D::date

Attempts:

3 left

💡 Hint

Common Mistakes

Not casting strings to dates before subtraction.

Using interval cast incorrectly.

Cast the strings to DATE, subtract them, and cast the result to interval type to get the difference in days.

Practice

1. Why is it important to use the DATE or TIMESTAMP types in PostgreSQL when working with dates?

easy

A. They automatically convert dates to strings for display.

B. They store dates as plain text for easy editing.

C. They allow accurate sorting and filtering of data by time.

D. They prevent any date values from being stored.

Solution

1. Step 1: Understand date types purpose

   DATE and TIMESTAMP types store date and time in a format PostgreSQL can understand and compare.

2. Step 2: Recognize benefits for sorting and filtering

   Using these types allows PostgreSQL to sort and filter data accurately by date/time values.

3. Final Answer:

   They allow accurate sorting and filtering of data by time. -> Option C

4. Quick Check:

   Date types enable correct time-based queries [OK]

Hint: Use DATE/TIMESTAMP to sort/filter dates correctly [OK]

Common Mistakes:

• Treating dates as plain text causes wrong sorting
• Assuming dates auto-convert to strings for display
• Ignoring the difference between DATE and TIMESTAMP

2. Which of the following is the correct way to declare a column named created_at that stores date and time in PostgreSQL?

easy

A. created_at TIMESTAMP

B. created_at DATE

C. created_at INT

D. created_at VARCHAR(20)

Solution

1. Step 1: Identify the data type for date and time

   To store both date and time, PostgreSQL uses the TIMESTAMP type.

2. Step 2: Compare options

   VARCHAR stores text, DATE stores only date without time, INT stores numbers, so TIMESTAMP is correct.

3. Final Answer:

   created_at TIMESTAMP -> Option A

4. Quick Check:

   Use TIMESTAMP for date and time columns [OK]

Hint: Use TIMESTAMP for date and time columns [OK]

Common Mistakes:

• Using VARCHAR instead of date/time types
• Using DATE when time is needed
• Using INT for date storage

3. Given the table events(event_name TEXT, event_date DATE), what will this query return?

SELECT event_name FROM events WHERE event_date > '2024-01-01';

medium

A. All events after January 1, 2024

B. All events on or before January 1, 2024

C. All events on January 1, 2024

D. Syntax error due to date format

Solution

1. Step 1: Understand the WHERE clause condition

   The condition event_date > '2024-01-01' filters events with dates strictly after January 1, 2024.

2. Step 2: Interpret the query result

   The query returns event names where event_date is greater than January 1, 2024, excluding that date itself.

3. Final Answer:

   All events after January 1, 2024 -> Option A

4. Quick Check:

   event_date > '2024-01-01' means dates after that day [OK]

Hint: Remember > excludes the date itself [OK]

Common Mistakes:

• Confusing > with >= operator
• Thinking the date format causes errors
• Assuming it includes the date '2024-01-01'

4. You wrote this query to find events on March 15, 2024:

SELECT * FROM events WHERE event_date = '15-03-2024';

But it returns no rows. What is the likely problem?

medium

A. The event_date column is not indexed.

B. The date format '15-03-2024' is not recognized by PostgreSQL.

C. The table name is incorrect.

D. The query needs a TIMESTAMP instead of DATE.

Solution

1. Step 1: Check date format used in query

   PostgreSQL expects dates in 'YYYY-MM-DD' format by default, not 'DD-MM-YYYY'.

2. Step 2: Understand why no rows returned

   Because '15-03-2024' is not recognized as a valid date, the condition matches no rows.

3. Final Answer:

   The date format '15-03-2024' is not recognized by PostgreSQL. -> Option B

4. Quick Check:

   Use 'YYYY-MM-DD' format for dates [OK]

Hint: Use ISO date format YYYY-MM-DD [OK]

Common Mistakes:

• Using DD-MM-YYYY instead of YYYY-MM-DD
• Assuming PostgreSQL auto-converts date formats
• Blaming indexing or table name for no results

5. You want to find all events that happened in the year 2023 using the events(event_date DATE) table. Which query correctly returns these events?

hard

A. SELECT * FROM events WHERE event_date BETWEEN '2023-01-01' AND '2023-12-31';

B. SELECT * FROM events WHERE EXTRACT(YEAR FROM event_date) = 2023;

C. SELECT * FROM events WHERE event_date >= '2023-01-01' AND event_date < '2024-01-01';

D. All of the above

Solution

1. Step 1: Analyze SELECT * FROM events WHERE event_date BETWEEN '2023-01-01' AND '2023-12-31';

   Using BETWEEN with '2023-01-01' and '2023-12-31' includes all dates in 2023.

2. Step 2: Analyze SELECT * FROM events WHERE EXTRACT(YEAR FROM event_date) = 2023;

   EXTRACT(YEAR FROM event_date) = 2023 filters events in 2023 by extracting the year part.

3. Step 3: Analyze SELECT * FROM events WHERE event_date >= '2023-01-01' AND event_date < '2024-01-01';

   Using >= '2023-01-01' and < '2024-01-01' also correctly selects all 2023 dates.

4. Final Answer:

   All of the above -> Option D

5. Quick Check:

   Multiple correct ways to filter by year [OK]

Hint: Use BETWEEN, EXTRACT, or range for year filtering [OK]

Common Mistakes:

• Using incorrect date ranges that exclude some days
• Forgetting to use < '2024-01-01' for inclusive year end
• Assuming only one method works for year filtering