TO_CHAR for date formatting in PostgreSQL - Step-by-Step Execution

Concept Flow - TO_CHAR for date formatting

Start with a DATE or TIMESTAMP value

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Apply TO_CHAR function with format string

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TO_CHAR converts date to text

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Output formatted string

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Use result in query or display

TO_CHAR takes a date or timestamp and a format pattern, then returns a text string formatted as specified.

Execution Sample

PostgreSQL

SELECT TO_CHAR('2024-06-15'::date, 'DD Mon YYYY');

Formats the date June 15, 2024 as a string like '15 Jun 2024'.

Execution Table

Step	Input Date	Format String	TO_CHAR Output	Explanation
1	2024-06-15	'DD Mon YYYY'	'15 Jun 2024'	TO_CHAR reads date and applies format: day number, abbreviated month, full year
2	2024-06-15	'YYYY/MM/DD'	'2024/06/15'	Format changes to year/month/day with slashes
3	2024-06-15	'FMDay, DDth Month YYYY'	'Saturday, 15th June 2024'	FM removes padding, literal 'th' after day number, full month name
4	2024-06-15	'HH24:MI:SS'	'00:00:00'	Time part defaults to midnight for date input
5	2024-06-15	'YYYY-MM-DD'	'2024-06-15'	Standard ISO date format output
6				Execution ends after formatting the input date

💡 All formatting options applied, TO_CHAR returns formatted text string

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Input Date	2024-06-15	2024-06-15	2024-06-15	2024-06-15	2024-06-15	2024-06-15	2024-06-15
Format String		'DD Mon YYYY'	'YYYY/MM/DD'	'FMDay, DDth Month YYYY'	'HH24:MI:SS'	'YYYY-MM-DD'	'YYYY-MM-DD'
TO_CHAR Output		'15 Jun 2024'	'2024/06/15'	'Saturday, 15th June 2024'	'00:00:00'	'2024-06-15'	'2024-06-15'

Key Moments - 3 Insights

Why does TO_CHAR output '00:00:00' for time when formatting a date?

Because the input is a date without time, PostgreSQL treats the time as midnight (00:00:00). See execution_table row 4.

What does 'FM' do in the format string?

'FM' removes padding spaces from the output, so day and month names are not padded. See execution_table row 3.

Why is the output a text string and not a date?

TO_CHAR always returns text because it formats the date into a readable string. This is shown in all output values in execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the TO_CHAR output at step 2?

A '2024/06/15'

B '15 Jun 2024'

C 'Saturday, 15th June 2024'

D '00:00:00'

💡 Hint

Check the 'TO_CHAR Output' column in execution_table row 2.

At which step does the format string include an ordinal suffix like 'th'?

A Step 1

B Step 3

C Step 4

D Step 5

💡 Hint

Look for 'DDth' in the 'Format String' column in execution_table.

If the input was a timestamp with time 14:30:00, what would TO_CHAR output for format 'HH24:MI:SS'?

A '2024-06-15'

B '00:00:00'

C '14:30:00'

D '15 Jun 2024'

💡 Hint

Refer to execution_table row 4 and imagine input time is not midnight.

Concept Snapshot

TO_CHAR(date, format) converts a date or timestamp to text.
Use format patterns like DD (day), Mon (month abbrev), YYYY (year).
FM removes padding spaces.
Output is always text, not date.
Useful for readable date display in queries.

Full Transcript

TO_CHAR is a PostgreSQL function that formats dates or timestamps into readable text strings. You give it a date and a format pattern, and it returns the date as text formatted as you want. For example, 'DD Mon YYYY' turns June 15, 2024 into '15 Jun 2024'. If you use 'FM' in the format, it removes extra spaces. When you format a date without time, the time defaults to midnight '00:00:00'. The output is always text, so you can display or use it as a string in your queries.

Practice

1. What does the PostgreSQL function TO_CHAR do when used with a date?

easy

A. It converts the date into a formatted text string.

B. It changes the date into a number representing days.

C. It adds days to the date value.

D. It deletes the date from the database.

Solution

1. Step 1: Understand TO_CHAR purpose

   The TO_CHAR function is used to convert dates or numbers into text with a specific format.

2. Step 2: Apply to date values

   When used with a date, it changes the date into a string that looks like the format you choose (e.g., 'YYYY-MM-DD').

3. Final Answer:

   It converts the date into a formatted text string. -> Option A

4. Quick Check:

   TO_CHAR formats date to text [OK]

Hint: TO_CHAR turns dates into readable text formats [OK]

Common Mistakes:

• Thinking TO_CHAR changes the date value itself
• Confusing TO_CHAR with date arithmetic functions
• Assuming TO_CHAR returns a number

2. Which of the following is the correct syntax to format the current date as 'YYYY-MM-DD' using TO_CHAR in PostgreSQL?

easy

A. SELECT TO_CHAR(CURRENT_DATE, "YYYY-MM-DD");

B. SELECT TO_CHAR(CURRENT_DATE, 'YYYY-MM-DD');

C. SELECT TO_CHAR(CURRENT_DATE, YYYY-MM-DD);

D. SELECT TO_CHAR('YYYY-MM-DD', CURRENT_DATE);

Solution

1. Step 1: Check TO_CHAR function syntax

   The correct syntax is TO_CHAR(date_value, 'format_string') where the format is a string in single quotes.

2. Step 2: Identify correct option

   SELECT TO_CHAR(CURRENT_DATE, 'YYYY-MM-DD'); uses the date first, then the format string in single quotes, which is correct.

3. Final Answer:

   SELECT TO_CHAR(CURRENT_DATE, 'YYYY-MM-DD'); -> Option B

4. Quick Check:

   TO_CHAR(date, 'format') syntax [OK]

Hint: Format string must be in single quotes after date [OK]

Common Mistakes:

• Swapping arguments order
• Missing quotes around format string
• Using double quotes instead of single quotes

3. What is the output of this query?

SELECT TO_CHAR(DATE '2024-06-15', 'FMMonth DD, YYYY');

medium

A. June 15,2024

B. June 15 2024

C. June 15, 2024

D. June15, 2024

Solution

1. Step 1: Understand format pattern

   The format 'FMMonth DD, YYYY' means full month name without padding, day with two digits, comma, space, then four-digit year.

2. Step 2: Apply to given date

   For '2024-06-15', the month is June, day 15, year 2024, so output is 'June 15, 2024'.

3. Final Answer:

   June 15, 2024 -> Option C

4. Quick Check:

   FMMonth DD, YYYY = June 15, 2024 [OK]

Hint: FMMonth avoids space padding, watch commas carefully [OK]

Common Mistakes:

• Forgetting FM modifier causing space padding in 'Month'
• Missing comma or space after day
• Confusing 'Month' with 'Mon' abbreviation

4. Identify the error in this query:

SELECT TO_CHAR(NOW(), YYYY-MM-DD);

medium

A. NOW() cannot be used with TO_CHAR.

B. TO_CHAR requires three arguments.

C. YYYY-MM-DD is not a valid format pattern.

D. Missing single quotes around the format string.

Solution

1. Step 1: Check format string usage

   The format pattern must be a string enclosed in single quotes.

2. Step 2: Identify error in query

   The query uses YYYY-MM-DD without quotes, causing a syntax error.

3. Final Answer:

   Missing single quotes around the format string. -> Option D

4. Quick Check:

   Format string needs quotes [OK]

Hint: Always put format patterns in single quotes [OK]

Common Mistakes:

• Forgetting quotes around format
• Thinking NOW() is incompatible
• Adding extra arguments to TO_CHAR

5. You want to display the current timestamp as 'DD/MM/YYYY HH24:MI' (day/month/year hour:minute). Which query correctly formats it using TO_CHAR?

hard

A. SELECT TO_CHAR(NOW(), 'DD/MM/YYYY HH24:MI');

B. SELECT TO_CHAR(NOW(), 'MM-DD-YYYY HH:MI');

C. SELECT TO_CHAR(CURRENT_TIMESTAMP, 'DD-MM-YYYY HH24:MI');

D. SELECT TO_CHAR(CURRENT_DATE, 'DD/MM/YYYY HH24:MI');

Solution

1. Step 1: Identify correct format pattern

   The required format is day/month/year with slashes and 24-hour time with minutes: 'DD/MM/YYYY HH24:MI'.

2. Step 2: Choose correct function and format

   Use NOW() or CURRENT_TIMESTAMP for current timestamp. SELECT TO_CHAR(NOW(), 'DD/MM/YYYY HH24:MI'); matches the format exactly.

3. Final Answer:

   SELECT TO_CHAR(NOW(), 'DD/MM/YYYY HH24:MI'); -> Option A

4. Quick Check:

   Exact format with NOW() and slashes [OK]

Hint: Match format string exactly with desired output [OK]

Common Mistakes:

• Using CURRENT_DATE which lacks time
• Mixing date separators (slashes vs dashes)
• Using 12-hour format without AM/PM