Date and time functions

Introduction to Redshift

Jason Myers

Principal Architect

Getting current date and time

SYSDATE date and time at transaction start

-- Get current date and time
SELECT SYSDATE;

timestamp
============================
2024-01-27 20:05:55.976353

GETDATE() date and time at statement start, requires parenthesis

-- Get current date and time
SELECT GETDATE();

timestamp
============================
2024-01-27 20:06:55.976353

Date and time function behavior

Watch out for leader node-only functions!

DATEDIFF over AGE
GETDATE/SYSDATE over leader-specific functions:
- CURRENT_TIME
- CURRENT_TIMESTAMP
- ISFINITE
- LOCALTIME
- LOCALTIMESTAMP
- NOW

Truncating dates and times

TRUNC returns a date from a timestamp

-- Get current date based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
SELECT TRUNC(SYSDATE);

2024-01-27

DATE_TRUNC('datepart', timestamp) truncates to a datepart like hour or day

-- Truncate to hour based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
SELECT DATE_TRUNC('minute', SYSDATE);

2024-01-27 20:05:55

¹ https://docs.aws.amazon.com/redshift/latest/dg/r_Dateparts_for_datetime_functions.html

Getting parts of dates and timestamps

DATE_PART(datepart, date or timestamp)
- extracts the requested part from a date or timestamp

-- Get current month based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
SELECT DATE_PART(month, SYSDATE);

Can return more than month, day, year
- Examples: dayofweek, quarter, timezone

-- Get current day of week based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
SELECT DATE_PART(dayofweek, SYSDATE);

Comparing dates and times

DATE_CMP(date_1, date_2) relative comparison
- Returns -1 if date_1 is earlier
- Returns 0 if dates are equal
- Returns 1 if date_1 is later
Type specific functions
- DATE_CMP_TIMESTAMP
- DATE_CMP_TIMESTAMPTZ
- TIMESTAMP_CMP
- TIMESTAMP_CMP_TIMESTAMPTZ
- TIMESTAMPTZ_CMP

-- Compare 5 dates from a table based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
  SELECT date_col, 
         TRUNC(SYSDATE) AS current_date,
         DATE_CMP(date_col, SYSDATE)
    FROM combined_history_projections
ORDER BY date_col
   LIMIT 3;

 date_col  |  current_date | date_cmp
===========|===============|==========
2024-01-26 | 2024-01-27    |       -1
2024-01-27 | 2024-01-27    |        0
2024-01-28 | 2024-01-27    |        1

Calculating differences

DATEDIFF(datepart, value_1, value_2)
Supports date, time, timetz, or timestamp in either position
- Must contain the datepart
Returns
- a negative value if value_2 is earlier
- Returns 0 if dates are equal
- a positive value if value_2 is later

Using DATEDIFF

-- Days till end of first quarter based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
SELECT DATEDIFF(day,TRUNC(SYSDATE),'2024-03-31') AS days_diff;

days_diff
===========
64

Incrementing dates and times

DATEADD(datepart, quantity, value)
Supports date, time, timetz, or timestamp
Quantity can be negative to subtract

-- Add week to a date based on 
-- SYSDATE of 2024-01-27 20:05:55.976353
SELECT TRUNC(SYSDATE) AS todays_date,
       TRUNC(DATEADD(week, 1, SYSDATE)) AS next_weeks_date;

todays_date | next_weeks_date
============|==================
2024-01-27  | 2024-02-03

Incrementing dates and times... gotchas

Leap years by month return end of month

-- Add year by months to a date
SELECT DATEADD(month, 12, '2024-02-29');

2025-02-28 00:00:00

Leap years by year return next day

-- Add year by year to a date
SELECT DATEADD(year, 1, '2024-02-29');

2025-03-01 00:00:00

Let's practice!

Introduction to Redshift