I am converting a postgres app to an Oracle app. 9. 662522'); date_trunc --------------------- 2022-05-16 12:00:00. SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 1. Syntax DATE_TRUNC(‘[interval]’, time_column) The time_column is the database column that contains the timestamp you'd like to round, and [interval] dictates your desired precision level. To have one row per minute, even when there's no data, you'll want to use generate _ series. The first day of a week (for format element 'week') is defined by the parameter NLS_FIRST_DAY_OF_WEEK (also see ALTER SESSION and ALTER SYSTEM ). If you don't have new users every minute, you're going to have gaps in your data. Postgres has lots of functions for interval and overlap so you can look at data that intersects. It’s possible in Postgres to truncate or round a given timestamp to some given level of precision. All the functions and operators described below that take time or timestamp inputs actually come in two variants: one that takes time with time zone or timestamp with time zone, and one that takes time without time zone or timestamp without time zone. 指定した単位（month）以下の値が切り捨てられ、 年 月という結果. The syntax of the function is as follows: DATE_TRUNC ('precision', expression); where expression is a timestamp or an interval to truncate. I found these two procedures that abstract equivalent logic: CREATE OR REPLACE FUNCTION first_of_week(date) returns date AS $$ SELECT ($1::date-(extract('dow' FROM $1::date)*interval '1 day'))::date; $$ LANGUAGE SQL STABLE STRICT; CREATE OR. where precision is the precision to which you want to truncate the date or time (e. created), 'YYYY-MM-DD')) GROUP BY d. PostgreSQL provides a number of functions that return values related to the current date and time. It's best explained by example: date_trunc('hour',TIMESTAMP '2001-02. Formats timestamp as a string using format. To generate a series of dates this is the optimal way: SELECT t. The date_trunc function truncates a TIMESTAMP or an INTERVAL value based on a specified date part e. 1. g. Syntax: add_months(date, integer). 2017) DAY , DAYOFMONTH. ) This function takes two arguments. 9. Working with DATE, TIMESTAMP, and INTERVAL in PostgreSQL can be confusing. SPLIT_PART. The function always returns a DATE. If you want to get the start of the month of the "timestamp" value, there are easier way to do that: date_trunc ('month', ' { { date. “Year” must be passed. date_trunc () The return type of the date_trunc function is a timestamp. date_trunc (field, source [, time_zone ]) source is a value expression of type timestamp, timestamp with time zone, or interval. for example, in postgresql. (Values of type date and time are cast automatically to timestamp or. SELECT date_trunc. PostgreSQL provides a number of functions that return values related to the current date and time. 1) precision The precision argument specifies fractional seconds precision of the second. This function can also truncate a number. One way to do this is to "truncate" the date to the start of the month, then add 8 days: vardate := date_trunc ('month', vardate)::date + 8; date_trunc returns a timestamp that's why the cast ::date is needed. source is a value expression of type timestamp or interval. 9. PostgreSQLのTIMESTAMP型で値を入れた日時データについて、小数点以下の秒数を「切り捨て」して取得する方法を紹介する。 まずは結論から。 以下のとおり、 date_trunc 関数を使うことで小数点以下を「切り捨て」して取得することができる。In the docs I could only find a way to create a date from a string, e. 3. SELECT date_trunc. Which date function I should use to build such an interval? postgresql postgresql-9. date_trunc() also accepts other values, for instance quarter, year etc. I would suggest not thinking too hard about the problem and just using the first date/time of the month. sql. The GROUP BY clause in Postgres allows us to group the table’s data based on specific column(s), making it easy to analyze and understand relationships and patterns within your data. This uses PostgreSQL’s date_trunc () function, along with some date arithmetic to return the results we want. 9. Based on the parts extracted, create a new datetime. Sorted by: 2. Because that’s the way it’s implemented in Postgres and DB2. date, q1. Isolating hour-of-day and day-of-week with EXTRACT function. This is where PostgreSQL can help us with some date functions. SELECT date_trunc ('hour', date1) AS hour_stump , (extract (minute FROM date1)::int / 5) AS min5_slot , count (*) FROM table1 GROUP BY 1, 2 ORDER BY 1, 2; You could GROUP BY two columns: a timestamp truncated to the hour and a 5-minute-slot. TRUNC(timestamp) Arguments. I am using this script to create and populate a partly localized (for Turkish) date dimension table. One truncates a date to the precision specified (kind of like rounding, in a way) and the other just returns a particular part of a datetime. date_trunc ( field, source [, time_zone ]) source is a value expression of type timestamp, timestamp with time zone, or interval. yosihisa@jp. For example, because the common calendar starts from the year 1, the first decade (decade 1) is 0001-01-01 through 0009-12-31, and the second decade (decade 2) is 0010-01-01 through 0019-12-31. Learn how to round or truncate timestamps in PostgreSQL for effective time-based grouping using the date_trunc function. To store date values, you use the PostgreSQL DATE data type. 32 shows the available functions for date/time value processing, with details appearing in the following subsections. config. This function truncates a date/time value to a specified precision. 2: I've chosen "date_period" to be just one day (and, in some places, formatted the result for ease of display). A weird way to number weeks but might be what the OP is after :) – Andomar. PostgreSQL 13. Use the function date_trunc() instead,. toLocalDateTime () When you use date_trunc ('day', now () at time zone 'Asia/Tehran') (column tehran_local_start_of_today) it indicates the start of today in Tehran local. SELECT ID, Quarter, Value/3 AS "Value", CASE WHEN Quarter = 1 THEN '2020-01-01' WHEN Quarter = 2 THEN '2020-04-01' END AS "Start_Date", CASE WHEN. SyntaxThe goal is to extract a portion out of a timestamp. To return. DATE '2000-01-02'. select * from table where extract (hour from column1) in (8, 9) where cast (column1 as time) >= '8:00' and column1::time < '10:00'. How do I get the quarter end date nicely?The way to count weeks is to truncate the start and end timestamps to the first day of the week, then subtract days. Summary: in this tutorial, we will introduce you to the PostgreSQL DATE_PART() function that allows you to retrieve subfields e. Also, we can calculate time intervals using these functions that will help us. Extracting year from a timestamp: SELECT EXTRACT(YEAR. Syntax: date_trunc. Practical examples would include analyzing company’s quarterly. Any valid year (e. This is used in subquery cal to generate a list of all dates in your data. MONTH: For timestamp values, the number of the month within the year (1–12) ; for interval values the number of months, modulo 12 (0–11). The SELECT statement below extracts the quarter each. These queries work fine in oracle but am in the process of converting it to a postgres query but it complains. Table 9. For formatting functions, refer to Section 9. Delaying Execution. The SELECT statement below extracts the month from the date_renting column of the renting table. 16. of ("Asia/Tehran")). The cast to date ( day::date) does that implicitly. The DATE_TRUNC() function will truncate timestamp or interval data types to return a timestamp or interval at a specified precision. Q&A for work. When working with dates and times in PostgreSQL, having a date calendar table can be incredibly useful. If the contraint should apply to the tservice as type "date" you might as well create the tservice column as type "date" instead. Table 9-28 shows the available functions for date/time value processing, with details appearing in the following subsections. RTRIM. RPAD (‘ABC’, 6, ‘xo’) ‘ABCxox’. Everything to the “right” of the datepart you selected will be “blank” or go back to the beginning (in other words, if you truncate your query at year, then the month, day and time will “reset” to 01-01 00:00). Explained below with examples: Example 1: Fiscal Year system: Apr to Mar From Date: Jan-05-2008 To Date: May-15-2008. Remove the longest string that contains specified characters from the right of the input string. date 、 time 、または timestamp を指定された精度に切り捨てます。. 1. Current Date/Time. The Oracle TRUNC() function returns a DATE value truncated to a specified unit. Functions and Operators. l_date is the column where I would pull the date from. They are both the same. In Postgresql, to truncate or extract the week of the timestamp value, pass the week as a string to the date_trunc function. SELECT q1. quarter: Quarter (1 to 4) second: Seconds (and fractional. DROP TABLE if exists d_date; CREATE TABLE d_date. These functions all follow a common calling convention: the first argument is the value to be. To get week start and end date (as 0 for Monday and 4 for Friday): select cast (date_trunc ('week', current_date) as date) + 0 || '-->' || cast (date_trunc ('week', current_date) as date) + 4; 2015-08-17-->2015-08-21. Is that what you want?Use union all:. If you want just the date in the current time zone, cast to a date. Overall, it’s a great function to use to help you aggregate your data into specific date parts while keeping a date format. source must be a value expression of type timestamp, time, or interval. 6. Use the aggregate FILTER clause in Postgres 9. WW truncates date to the nearest previous day same to the first day of week of the year. EXTRACT, date_part EXTRACT(field FROM source)The extract function retrieves subfields such as year or hour from date/time values. 9. Part of AWS Collective. DATE '2000-01-02'. pto_start_date < (date_trunc ('quarter', now () - INTERVAL '1 month') + INTERVAL. I want to generate date data using postgresql function "generate_series" , however I have only advanced as far as the following: SELECT ( DATE_TRUNC( 'month', ld ) + '1 month'::INTERVAL -. date_trunc ('hour', created) + extract (minute from created)::int / 15 * interval '15' minute. Share. Get the number of remaining days after excluding date ranges in a table. Section 9. 9. 9. Truncates a DATE value. Current Date/Time. 8. You can then manipulate this output (with strftime. This PostgreSQL tutorial explains how to use the PostgreSQL date_part function with syntax and examples. Here is how you can convert an epoch value back to a time stamp: SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 982384720 * INTERVAL '1 second'; hour. you need to qualify the field with the table name. In the above output, it shows the output like a day of the timestamp value but we can find the. 'QUARTER' First day of its quarter. The date_trunc function in redshift is specifically used to truncate the specified precision. Let’s add a year to any date. To return. Take two easy steps to create date_trunc: Break down the datetime into small parts (Year, Month, Day/Hour, Minute, Second) and extract the parts you need. DATE_FROM_UNIX_DATE. 789'); date_trunc 2020-04-01 00:00:00 Truncate the input timestamp to the first day of a year. trunc; Date/Time Functions. 8. The functions in this section use a format string that is compatible with JodaTime’s DateTimeFormat pattern format. age; current_date; current_time; current_timestamp; date_part; extract; localtime;. It puts that value in. SELECT date_trunc('MONTH', dtCol)::date; But getting the last day is not so straight forward. 日付や時刻を指定のところ（精度といいます）で切り捨てるには、 date_trunc関数 を使います。. May I make a request that "Quarter" should be treated as a valid Interval (as a synonym for "3 months"), to be consistent with other date functions that allow it, such as date_trunc() and extract() ? #1. Syntax. The syntax is: date_trunc ('hour', columnName). See below. 2k 3 64 88. One truncates a date to the precision specified (kind of like rounding, in a way) and the other just returns a particular part of a datetime. parse_datetime(string, format) → timestamp with time zone. EXTRACT (part FROM date) We state the type of extraction we want as part and then the source to be extracted date. Improve this answer. I have to convert a postgres query to Sequelize query. Sorted by: 3. PostgreSQL date_part function will allow retrieving subfields from the date and time value, e. timestamp)) from rollup_days as rp; To convert the timestamp back to a bigint, use extract ()Use the date_trunc method to truncate off the day (or whatever else you want, e. This is a timestamp with time zone value which refers in fact to 23:59:59 on sunday, but with 2 hours of difference with UTC time, depends on your locale and settings. The date_trunc function contains the two input parameters, i. (Values of type date and time are cast. Examples. 1) below the day precision (first parameter) the time zone offset of the result is always the same as the second parameters' offset. Interprets an INT64 expression as the number of days since 1970-01-01. However, with Postgres 14, the EXTRACT function now returns a numeric type instead of an 8-byte float. In simple terms,. I have tried using something like: SELECT DATE_TRUNC('quarter', TIMESTAMP '20200430 04:05:06. Current Date/Time. 9. 2017) YEAROFWEEK [1] Year that the extracted week belongs to. DATE_TRUNC truncates the Postgres timestamp to a specified precision. (Values of type date and time are cast automatically to timestamp or interval, respectively. select cast (date_trunc ('month', current_date) as date) 2013-08-01. Table 9. 1 Answer. CREATE. 2. 切り捨ては抽出とは異なります。例： タイムスタンプを四半期まで切り捨てると、入力タイムスタンプの四半期の最初の日の真夜中に対応するタイムスタンプが返されます。 The PostgreSQL DATE_TRUNC function is used to truncate the date and time values to a specific precision (into a whole value), such as 'year', 'month', 'day', 'hour', 'minute', or 'second', in a string format. 11. From the documentation: date_part (): The date_part function is modeled on the traditional Ingres equivalent to the SQL-standard function extract: 2. What I need is to "round down" the month to day one, and I. The quarter of the year (1 - 4) that the date is in SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 1. ). Assuming you are using Postgres, you need quotes around your date constant and can convert to the right types: WHERE job_date >= DATE_TRUNC('month'::text, '2019. Syntax. It takes the date part ‘qtr’ from the timestamp value in the “created_at” column (from the “shopify_orders” table). We had discussed about the Date/Time data types in the chapter Data Types. ) field is an identifier or string that selects what field to. Neither of those expressions will make use of an index on created - you would need to create an expression based index with the expression used. (date_trunc('quarter', day)::date + '3 months - 1 day'::interval)::date AS quarter_ends_on, null AS is_end_of_quarter, null AS days_in_quarter,SELECT date_trunc($1, purchase_date) unit_of_time, SUM(total) FROM orders WHERE purchase_date >= $2 AND purchase_date <= $3 GROUP BY unit_of_time ORDER BY unit_time; [interval, startDate, endDate] The above query works correctly for when I pass in either 'month' or 'day' as the interval variable, but gives incorrect values. Well, In postgres, it seems there's no such function equivalent to LAST_DAY() available in oracle. Table 9-27 illustrates the behaviors of the basic arithmetic operators ( +, *, etc. How can i get. 31 illustrates the behaviors of the basic arithmetic operators ( +, *, etc. 9. PostgreSQL provides a number of functions that return values related to the current date and time. g. RTRIM (‘abcxxzx’, ‘xyz’) ‘abc’. The cast to date ( day::date) does that implicitly. LOCALTIME(precision) Arguments. Hey so im trying to query from a database, using Sequelize (Node. EXTRACT (field FROM source) The extract function retrieves subfields such as year or hour from date/time values. My current work around is to map date_trunc as a function and explicitly call it but it seems odd to have to do that. This can make date/time fields easier to read, as well as help perform cleaner time-based analyses. It shows a similar result, converting the date to a month and year value, which changes the day to the first of that month. column. Stack Exchange Network Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to. dataset. 9. date_trunc () is a system function for truncating a timestamp or interval to a specified unit. day::date FROM generate_series (timestamp '2004-03-07' , timestamp '2004-08-16' , interval '1 day') AS t (day); Additional date_trunc () is not needed. DATE_TRUNC returns a date or timestamp, while DATE_PART returns a subfield from a date or timestamp. SELECT distinct (CASE WHEN {PERIOD} = 'Previous Quarter' AND pto. Postgres has lots of functions for interval and overlap so you can look at data that intersects. Here, I’ll try to show you how existing production PostgreSQL tables can be partitioned, while also presenting you with a few options and their trade-offs. SELECT date, region, revenue FROM sales WHERE date = (SELECT MAX(date) from sales WHERE date between date_trunc('quarter', CURRENT_DATE)::date -. The following illustrates the. GitHub Gist: instantly share code, notes, and snippets. Interprets an INT64 expression as the number of days since 1970-01-01. In PostgreSQL, various inbuilt functions like DATE_PART(), EXTRACT(), and DATE_TRUNC() are used with the GROUP BY clause to group the table’s data by a specific date field. 1. 9. Or simpler, use the column number: group by 1 (if the expression is the first column in the select clause). Introduction to the PostgreSQL date_trunc function. the Use of the DATE_TRUNC () Function in PostgreSQL. The table currently has nearly 5 million rows and this query currently takes 8 seconds to execute. PostgreSQL DATE_PART () function is mainly used to return the part of the date and time; the date_part function in PostgreSQL will subtract the subfield from the date and time value. By implementing the feature above, we are going to learn the following date functions in PostgreSQL: Truncate date with date_trunc; Extract date parts, such as weekday, month and year with date_part. 001 WHEN 'second' THEN 1. To see the objects provided by the extension, run dx+ orafce. SQL Server: Date truncation for custom time periods like year, quarter, month, etc. It’s possible in Postgres to truncate or round a given timestamp to some given level of precision. PostGreSQL : date_trunc() returns timestamp with timezone when used on date. date_trunc函数根据指定的日期部分（例如小时、周或月）截断一个TIMESTAMP或一个INTERVAL值，并以一定精度返回截断的时间戳或间隔值。[email protected]_trunc ('month',current_date) + interval '1 month' - interval '1 day'. Table 9-23 lists them. For formatting functions, refer to Section 9. You can fix a date or remove days from current day. 8. so you can distinct it first in the table then do the count. You can update the type of the column like this: ALTER TABLE your_table ALTER COLUMN tservice TYPE date; and then add the constraint like so:There are various DateTime functions as well as operators availabe in PostgreSQL. DATE_TRUNC (date, < Parameters. It can also truncate the value to a specified. Yes, that is how you use date_trunc. I would suggest not thinking too hard about the problem and just using the first date/time of the month. Postgres has plenty of date-specific functions -- from date_trunc() to age() to + interval-- to support dates. The range of values for date values in PostgreSQL is 4713 BC to 5874897 AD. The quarter of the year (1–4) that the date is in. Table 9. source must be a value expression of type timestamp, time, or. I have an sql query am trying to make to my postgres db. PostgreSQL uses 4 bytes to store a date value. 切り捨ては抽出とは異なります。例： タイムスタンプを四半期まで切り捨てると、入力タイムスタンプの四半期の最初の日の真夜中に対応するタイムスタンプが返されます。The PostgreSQL DATE_TRUNC function is used to truncate the date and time values to a specific precision (into a whole value), such as 'year', 'month', 'day', 'hour', 'minute', or 'second', in a string format. Exercise care with lower. If you do want to use BETWEEN (which will only work properly if date is defined with the data type date) then you can use: select * from my_table where date between date_trunc ('year', current_date - interval '1 year')::date and date_trunc ('year', current_date)::date - 1. Posted on July 24, 2020 by Ian In PostgreSQL, the date_trunc () function truncates a date/time value to a specified precision. Most texts you’ll find online will tell you that partitioning is done by executing x and y, end of story. Adding a month gives you the first of the following month. Add 1 if you prefer 1 - 12. performance. 4. In order to group our orders by month, in PostgreSQL we'll use the date_trunc built-in function. Postgres date_trunc quarter with a custom start month. Given a From Date, To Date and a Fiscal Year system, I want to get all the split-up duration within the given From & To Date based on the Fiscal Year system. Nice. If you want both quarter and year you can use date_trunc: SELECT date_trunc('quarter', published_date) AS quarter This gives the date rounded to the. 9. date_trunc is only defined for timestamp with time zone and timestamp inputs. timestamp. PostgreSQL is a powerful database and includes various functions for managing timestamps and date times. answered Aug 18, 2015 at 10:52. 0) $$ LANGUAGE SQL; Generally rounding up to. and if I run it in Jan 2013, then it should give me 31 Dec 2012. Also, you need to study the week in snowflake. date_trunc. Getting the first day is easy and can be done with date_trunc. Use the date_trunc method to truncate off the day (or whatever else you want, e. It takes a date part (like a decade, year, month, etc. DATE_FROM_UNIX_DATE. 9. Write queries for continuous periods as explicit range condition. 'QUARTER': truncate to the first date of the quarter. to_char and all of the formatting functions let you query time however you want. 2 Answers. The LOCALTIME function takes one optional argument:. field selects to which precision to truncate the time stamp value. This converts the date column my_date to date (cuts the time part) and if you cast it back into timestamp it gets the 0 time. The PostgreSQL LOCALTIME function returns the current time at which the current transaction starts. amount), DATE_TRUNC('quarter', orders. Add a comment. The EXTRACT() function returns a double precision value. 1 Share Follow The DATE_TRUNC () function is used to truncate a date, time, or timestamp to a specified interval, such as the day, week, or month, in PostgreSQL and SQL Server. This function is most widely used for creating time series and aggregating at a granular level. Special calculation is needed for week/quarter. Here is the syntax of the PostgreSQL date_trunc() function: date_trunc (field TEXT, source TIMESTAMP). 2. 2 Answers. Add a comment. The subtraction of timestamps yields an interval. Learn more about Teamsdate_trunc('hour', timestamp '2001-02-16 20:38:40') 2001-02-16 20:00:00: extract. SELECT cast (created_at as date) as created_at, count (created_at) FROM forms group by 1 ORDER BY created_at asc; If you want the date in a particular time zone, date_trunc with that time zone then cast to a date. 662522'); You can also use the date_trunc () function truncate a value of type interval, for. 1994-10-27. g. There is no function you want, but as said in postgresql wiki you can define function for youself: CREATE OR REPLACE FUNCTION round_time_10m (TIMESTAMP WITH TIME ZONE) RETURNS TIMESTAMP WITH TIME ZONE AS $$ SELECT date_trunc ('hour', $1) + INTERVAL '10 min' * ROUND (date_part ('minute', $1) / 10. 0) $$ LANGUAGE sql;The PostgreSQL DATE_TRUNC function is used to truncate the date and time values to a specific precision (into a whole value), such as 'year', 'month', 'day', 'hour', 'minute', or 'second', in a string format. The query below shows sample data of your user adding an other user with a session over two days (to demonstrate the principle) The subquery day_cnt calculates the minimal start date of the sessions and the count_days that is covered with the sessions. 9. values date_trunc ('MONTH', DATE ('2007-02-18')) Result: 2007-02-01 00:00:00. このクエリを実行すると以下の結果が得られる。. That is easy enough to add. Share. You. answered Dec 28, 2011 at 13:33. Stack Overflow. The following query SELECT the_date FROM date_trunc('day', timestamp with time zone '2001-01-1 00:00:00+0100') as the_date results to the_date 2000-12-31 00:00 Is there a way to tell . If you pass a DATE value, the function will cast it to a TIMESTAMP value. Delaying Execution. date_trunc (format, timestamp) [source] ¶ Returns timestamp truncated to the unit specified by the format. , hour, week, or month and. 12,516 ExpertMod8TB. SELECT SUM(orders. Sorted by: 3. select date_trunc('month',current_date)::date; ┌────────────┐ │ date_trunc │. Its Java equivalent is:Using the connect by trick for generating numbers you can extend that to generate dates and times…. Possible Values. Sorted by: 2. edited Aug 18, 2015 at 10:57. atZone (ZoneId. The date_part function is modeled on the traditional Ingres equivalent to the SQL -function extract: The precision values are a subset of the field identifiers that can be used with the EXTRACT() and DATE_PART() functions. ) field selects to which precision to truncate the input value. Right now the cod. 9. The date function used to truncate a date or datetime value to the start of a given unit of duration. Thanks, -Lars On Thu, 20 Jul 2000, Tom Lane wrote: > Lars. I have this problem. 9. Basically, there are two parameters we. PostgreSQL provides a number of functions that return values related to the current date and time. These SQL-standard functions all return values based on the start time of the. The quarter of the year (1 - 4) that the date is in. Current Date/Time. I have a slow query that generates a report of account activity per week over the past year. Example 1: Truncate a DATE value to the beginning of the month. ·. AS day_of_month, datum - DATE_TRUNC('quarter',datum)::DATE +1 AS day_of_quarter, EXTRACT. ) as we did for the EXTRACT code. timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00'. Here is how I make a standard quarterly score average with default quarter. g. This function allows us to extract a date part and group the records by date/time using the GROUP BY clause. By Admin August 9, 2023 August 9,. Table 9. 9. 1 Answer. Common culprits are: > > *) CASE expressions > *) COALESCE > *) casts > *) simple tranformational expressions > *) predicate string concatenation *) time/date functions, ie WHERE date_trunc( 'quarter', some_timestamp ) = '2014-1-1' Though, in this case it's probably much better to teach the parser how to turn that into a range expression. The full-list is available in the Postgres docs. . In the above query within the date_part() function, provided the two values, the unit or the component ‘hour’ and the CURRENT_TIMESTAMP function that returns the current time your system. Rabbit. DATE_TRUNC is very handy for aggregating your data by a particular date_part, like MONTH. The basic syntax of the DATE_TRUNC function is as shown below: DATE_TRUNC(precision, source); where precision is the precision to which you want to. In Postgres, you can use the EXTRACT(), DATE_TRUNC(), and DATE_PART() function to extract the month from a date field and then use the GROUP. Jun 27, 2014. The DATE_TRUNC function is useful when. 1. AT TIME ZONE. Syntax. date_trunc(text, timestamp) timestamp: Truncate to specified precision;. These SQL-standard functions all return values based on the start time of the current transaction:DATE_TRUNC.