EXTRACT function for date parts in PostgreSQL

Introduction

The EXTRACT function helps you get specific parts like year, month, or day from a date or time. It makes it easy to work with dates by focusing on just the part you need.

You want to find the year someone was born from their birthdate.

You need to get the month from a sales date to group sales by month.

You want to know the day of the week for a meeting date.

You want to calculate the hour from a timestamp to analyze busy hours.

You want to extract the quarter from a date to report quarterly results.

Syntax

PostgreSQL

EXTRACT(field FROM source)

field can be year, month, day, hour, minute, second, quarter, dow (day of week), etc.

source is a date, time, or timestamp value.

Examples

Gets the year part (2024) from the date.

PostgreSQL

SELECT EXTRACT(year FROM DATE '2024-06-15');

Gets the month part (6) from the timestamp.

PostgreSQL

SELECT EXTRACT(month FROM TIMESTAMP '2024-06-15 14:30:00');

Gets the day part (15) from the date.

PostgreSQL

SELECT EXTRACT(day FROM DATE '2024-06-15');

Gets the hour part (14) from the timestamp.

PostgreSQL

SELECT EXTRACT(hour FROM TIMESTAMP '2024-06-15 14:30:00');

Sample Program

This query extracts the year, month, day, and day of the week from the date '2024-06-15'.

PostgreSQL

SELECT
  EXTRACT(year FROM DATE '2024-06-15') AS year_part,
  EXTRACT(month FROM DATE '2024-06-15') AS month_part,
  EXTRACT(day FROM DATE '2024-06-15') AS day_part,
  EXTRACT(dow FROM DATE '2024-06-15') AS day_of_week_part
;

Important Notes

The day of week (dow) returns 0 for Sunday, 1 for Monday, and so on.

EXTRACT returns a number, so you can use it in calculations or comparisons.

You can use EXTRACT with timestamps to get time parts like hour, minute, and second.

Summary

EXTRACT helps get specific parts from dates or times easily.

Use it to focus on year, month, day, hour, and more.

It returns numbers you can use in your queries.

Practice

1. What does the EXTRACT function do in PostgreSQL when used with a date or timestamp?

easy

A. It adds days to the date.

B. It changes the date format to a string.

C. It retrieves a specific part like year, month, or day from the date or timestamp.

D. It deletes the time part from the timestamp.

Solution

1. Step 1: Understand the purpose of EXTRACT

   The EXTRACT function is designed to pull out specific parts such as year, month, day, hour, etc., from a date or timestamp value.

2. Step 2: Compare with other options

   Options B, C, and D describe different operations like formatting, adding days, or truncating time, which EXTRACT does not do.

3. Final Answer:

   It retrieves a specific part like year, month, or day from the date or timestamp. -> Option C

4. Quick Check:

   EXTRACT returns date parts = A [OK]

Hint: EXTRACT pulls out parts like year or month from dates [OK]

Common Mistakes:

• Thinking EXTRACT changes date format
• Confusing EXTRACT with date arithmetic
• Assuming EXTRACT removes time part

2. Which of the following is the correct syntax to extract the month from a timestamp column named created_at?

easy

A. EXTRACT(created_at, MONTH);

B. EXTRACT(MONTH FROM created_at);

C. EXTRACT('MONTH', created_at);

D. EXTRACT MONTH created_at;

Solution

1. Step 1: Recall correct EXTRACT syntax

   The correct syntax is EXTRACT(part FROM source), so to get month: EXTRACT(MONTH FROM created_at);

2. Step 2: Identify incorrect syntax forms

   Options A, B, and D use wrong argument order, quotes around part name, missing FROM keyword, or wrong punctuation.

3. Final Answer:

   EXTRACT(MONTH FROM created_at); -> Option B

4. Quick Check:

   EXTRACT(part FROM source) = C [OK]

Hint: Use EXTRACT(part FROM source) syntax exactly [OK]

Common Mistakes:

• Omitting FROM keyword
• Using quotes around part name
• Swapping argument order

3. Given the query:

SELECT EXTRACT(DAY FROM TIMESTAMP '2024-06-15 10:30:00');

What will be the output?

medium

A. 10

B. 6

C. 2024

D. 15

Solution

1. Step 1: Identify the part extracted

   The query extracts the DAY part from the timestamp '2024-06-15 10:30:00'. The day is 15.

2. Step 2: Confirm output value

   Other options represent month (6), year (2024), and hour (10), which are not extracted here.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   EXTRACT(DAY) = 15 [OK]

Hint: Match EXTRACT part with date component value [OK]

Common Mistakes:

• Confusing day with month or year
• Expecting full date output
• Ignoring time part in timestamp

4. What is wrong with this query?

SELECT EXTRACT('YEAR' FROM CURRENT_DATE);

medium

A. The part name YEAR should not be in quotes.

B. CURRENT_DATE cannot be used with EXTRACT.

C. Missing parentheses around CURRENT_DATE.

D. EXTRACT requires two arguments separated by a comma.

Solution

1. Step 1: Check syntax for EXTRACT part

   The part name like YEAR should be unquoted. Quotes cause syntax error.

2. Step 2: Verify other parts of query

   CURRENT_DATE is valid input, no parentheses needed, and EXTRACT uses FROM keyword, not comma.

3. Final Answer:

   The part name YEAR should not be in quotes. -> Option A

4. Quick Check:

   Part names unquoted in EXTRACT [OK]

Hint: Do not put quotes around date parts in EXTRACT [OK]

Common Mistakes:

• Using quotes around part names
• Adding commas instead of FROM
• Thinking CURRENT_DATE needs parentheses

5. You want to find all records from a table orders where the order was placed in the first quarter (January to March) of any year. Which query correctly uses EXTRACT to filter these records?

hard

A. SELECT * FROM orders WHERE EXTRACT(QUARTER FROM order_date) = 1;

B. SELECT * FROM orders WHERE EXTRACT('MONTH' FROM order_date) < 4;

C. SELECT * FROM orders WHERE EXTRACT(MONTH, order_date) IN (1, 2, 3);

D. SELECT * FROM orders WHERE EXTRACT(MONTH order_date) BETWEEN 1 AND 3;

Solution

1. Step 1: Understand quarter extraction

   PostgreSQL supports EXTRACT(QUARTER FROM date) which returns 1 for Jan-Mar, 2 for Apr-Jun, etc.

2. Step 2: Evaluate each option

   Options A (missing FROM), B (quotes around MONTH), and C (comma instead of FROM) have syntax errors. SELECT * FROM orders WHERE EXTRACT(QUARTER FROM order_date) = 1; correctly uses EXTRACT(QUARTER FROM order_date) = 1.

3. Final Answer:

   SELECT * FROM orders WHERE EXTRACT(QUARTER FROM order_date) = 1; -> Option A

4. Quick Check:

   Use EXTRACT(QUARTER) = 1 for first quarter [OK]

Hint: Use EXTRACT(QUARTER) = 1 for first quarter filtering [OK]

Common Mistakes:

• Missing FROM keyword
• Using quotes around part names
• Using comma instead of FROM
• Not knowing EXTRACT supports QUARTER