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DateTime variables store important information, such as the date, time, and timezone for when a transaction took place or when a new entry was made in your PostgreSQL tables. Date and time features are not only helpful for finance and e-commerce, but also for data science projects where you are training models or performing feature engineering.
PostgreSQL is an excellent open-source, fully-featured Relational Database Management System (RDBMS) developed by the PostgreSQL Global Development Group. It has been in use for over 20 years and is a multi-paradigm database to support relational, object-relational, JSON, XML, and graph data types.
PostgreSQL has had a reputation for being a reliable, feature-rich, and performance-rich utility from its beginnings. Every release is very carefully controlled, and PostgreSQL beta releases are subject to at least a month’s testing. A number of businesses rely on PostgreSQL as their primary data storage/data warehouse for online, mobile, geospatial, and analytics applications.
PostgreSQL runs on all major operating systems, including Linux, UNIX (AIX, BSD, HP-UX, SGI IRIX, Mac OS X, Solaris, Tru64), and Windows.
Open-Source
: PostgreSQL is an Object-Relational Database Management System (ORDBMS). This allows PostgreSQL to provide both Object-Oriented and Relational Database functionality. It is a free-to-use Open-Source ORDBMS.
Prominent User Base:
PostgreSQL users include prominent names like Apple, Cisco, Etsy, Facebook, Instagram, Red Hat, Skype, Spotify, and Yahoo, to name a few.
Multiversion Concurrency Control
: To manage concurrent requests, PostgreSQL features a multi-version concurrency control which gives each transaction a “snapshot” of the database, allowing changes to be made without affecting other transactions. This largely eliminates the need for read locks, and ensures the database maintains ACID principles.
Reliability and Standards Compliance
: PostgreSQL’s write-ahead logging makes it a fault-tolerant database. Its large base of open source contributors lends it a built-in community support network. PostgreSQL is ACID compliant, and has full support for foreign keys, joins, views, triggers, and stored procedures, in many different languages.
A Supportive Community
: PostgreSQL offers a dedicated community that is always available to you. Private, third-party support services are also available. The community updates the PostgreSQL platform via the PostgreSQL Global Development Group.
Why Work With PostgreSQL Convert DateTime to Date Functions?
DateTime formats are essential to every business. Whether you are a financial analyst, who examines financial transactions, or a supply chain manager who maintains inventory records, DateTime formats help you record and identify every time-related element for your business transactions. This includes dates, hours, minutes, seconds, or even days of the week, months, and years when a transaction took place or when a new record was created in your PostgreSQL database.
Usually, DateTime formats include three data types: DATE, TIME, and TIMESTAMP. These data types are commonly used in relational databases like PostgreSQL, and MySQL and programming languages like Python. Being able to extract the necessary pieces of information, for example, date from these DateTime formats is an important skill that can further improve your understanding of data and help you better in Data Analysis.
In the upcoming sections of the PostgreSQL convert DateTime to date guide, we explore various examples to help you clean your data, perform PostgreSQL format date and extract the required pieces of information from DateTime formats.
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Suppose you have a timestamp column in your PostgreSQL table of customers that contains records of when they successfully completed a transaction on your website. Your timestamp columns may or may not contain timezone information. Let’s assume that your system has recorded DateTime information in the format “YYYY/MM/DD/HH24:MI:ss” and your sales manager wants information about the daily sales made during the month of October.
Using the
DATE()
function in PostgreSQL you can extract date values from your timestamp column. A simple SQL query does the job to yield the date values from “
customer_transactions
” that contain timestamp values.
SELECT DATE(customer_transaction) FROM customers;
PostgreSQL Convert DateTime to Date From a Specific Timestamp
One other way using which you can extract date values from a specific timestamp comes through the use “::” operator followed by the “DATE” keyword.
With this method, you can either perform a specific Postgres convert timestamp to date or convert the current timestamp (using the
now()
function) to date.
For example, let’s assume you have a timestamp ‘2022-07-07 07:37:33’ from which you need to extract the date field. The following SQL query in PostgreSQL helps you do so:
Or, assume that you want to extract today’s date from the current timestamp. The
now()
function in PostgreSQL returns the current date and time with timezone and you can use the following SQL query to perform PostgreSQL convert DateTime to date operation.
PostgreSQL relational database offers a variety of in-built functions like TO_CHAR(), EXTRACT(), and DATE_PART() to help you perform PostgreSQL convert DateTime to date operation. Have a look at those PostgreSQL convert DateTime to date functions in the upcoming sections.
PostgreSQL Format Date Using TO_CHAR() Function
In PostgreSQL relational databases, the
TO_CHAR()
function converts various data types like timestamp, interval, integer, floating-point, or numeric value to a formatted string. It has a simple syntax as given below.
TO_CHAR(expression, format)
The
expression
argument takes in the data types like timestamp, interval, integer, floating-point, or a numeric value that you wish to convert to a string as an input. The
format
argument specifies the format of the resultant string, which can be provided using multiple options as
Format
Description
HH
Hour of the day (01-12)
HH12
Hour of the day in 12-hour format (01-12)
HH24
Hour of the day in 24-hour format (00-23)
MI
Minute of the hour (00–59)
SS
Second of the minute (00–59)
MS
Millisecond (000–999)
US
Microsecond (000000–999999)
AM, am, PM or pm
Meridiem indicator (without periods)
A.M., a.m., P.M. or p.m.
Meridiem indicator (without periods)
YYYY
Calendar year (4 or more digits)
YYY
Calendar year (last 3 digits)
YY
Calendar year (last 2 digits)
Y
Calendar year (last digit)
MONTH
Name of the month in uppercase
Month
Name of the month in capitalized form
month
Name of the month in lowercase
MON
Abbreviated month name in uppercase (first 3 characters)
Mon
Abbreviated month name in capitalized form (first 3 characters)
mon
Abbreviated month name in lowercase (first 3 characters)
MM
Month number (01-12)
DAY
Name of the day in uppercase
Day
Name of the day in capitalized form
DY
Abbreviated day name in uppercase (first 3 characters)
Dy
Abbreviated day name in capitalized form (first 3 characters)
dy
Abbreviated day name in lowercase (first 3 characters)
DDD
Calendar year day (001–366)
DD
Month day (01-31)
D
Weekday (Sunday (1) to Saturday (7))
W
Week number of the month (1–5)
WW
Week number of the year (1-53)
Q
Quarter of the year
RM
Name of the month in uppercase Roman numerals (I–XII; I=January)
TZ
The abbreviated timezone in uppercase (only supported in to_char)
tz
The abbreviated timezone in lowercase (only supported in to_char)
TZH
Time-zone hours
TZM
Time-zone minutes
Along with these formats, PostgreSQL also offers certain
modifiers
for PostgreSQL convert DateTime to date operation. These are:
Modifier
Description
Example
FM prefix
Fill mode (suppress leading zeroes and padding blanks)
FMMonth
TH suffix
List ordinal number suffix in uppercase
DDTH, e.g., 07th
th suffix
List ordinal number suffix in lowercase
DDth, e.g., 07th
FX prefix
Use fixed format global option
FX Month DD Day
TM prefix
Translation mode
TMMonth
SP suffix
Spell mode
DDSP
You can refer to usage notes for PostgreSQL format date using formats or modifiers in the
PostgreSQL documentation
.
Coming back to our problem of Postgres convert timestamp to date, you might, at this point, be wondering how to use these options.
Here’s an example to help you understand. Let’s use the same example of the
customer_transactions
timestamp column which we had taken earlier. When you execute a SQL query like this,
The TO_CHAR() function in PostgreSQL returns a column
transaction_time, by
extracting time and converting it in 12-hour format from the
customer_transaction
timestamp column.
Here’s what the result would look like:
customer_transaction
transaction_time
2022-05-11 22:16:43
10:16:43
2022-05-11 22:18:37
10:18:37
2022-05-12 23:24:40
11:24:40
2022-05-12 20:19:57
08:19:57
Similarly, a SQL query like this will help you extract the date from your
customer_transactions
timestamp column.
This SQL query will extract the date from the current timestamp in the format ‘dd-mm-yyyy’. If you wish to select only the day number, you can use the following SQL query.
You can have multiple date formats of your choice, using the different formats mentioned above in the format table. The final conversion of the current date into the format that you specify in the query will be displayed on the console with the help of the “SELECT” statement as these arguments are finally passed on to the “TO_CHAR” function. Next, in our PostgreSQL convert DateTime to date guide, we discuss the EXTRACT() function.
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In this section of PostgreSQL convert DateTime to Date, we discuss the PostgreSQL function called the
EXTRACT()
function. The EXTRACT() function in PostgreSQL helps in fetching date subfields such as year or hour from DateTime. Sometimes you might just want to extract a specific part of the date, let’s say, the calendar year, month, or day, and in those scenarios, you can use the EXTRACT() function.
PostgreSQL EXTRACT() function has the following syntax:
EXTRACT(field FROM source)
EXTRACT() function takes in two arguments, field and source. The field argument specifies the date part, i.e. month, decade, hour, to extract from the DateTime value. The source argument is a value of type TIMESTAMP or INTERVAL.
Again, PostgreSQL offers a lot of options under the field argument. These are listed below:
Field Value
TIMESTAMP
Interval
CENTURY
Century
Number of centuries
DAY
Day of the month (1-31)
Number of days
DOY
Day of the year (1-366)
N/A
DOW
Day of the week (Sunday (0) to Saturday (6))
N/A
EPOCH
Time in number of seconds since 1970-01-01 00:00:00 UTC
Number of seconds in the interval
HOUR
Hour of the day (0-23)
Number of hours
MICROSECONDS
The seconds field, including fractional parts, multiplied by 1000000
The seconds field, including fractional parts, multiplied by 1000000
MILLENNIUM
The millennium
Number of millennium
MILLISECONDS
The seconds field, including fractional parts, multiplied by 1000
The seconds field, including fractional parts, multiplied by 1000
MINUTE
Minute of the hour (1-59)
Number of minutes
MONTH
Month of the year (1-12)
Number of months, modulo (0-11)
QUARTER
Quarter of the year
Number of quarters
SECOND
Second of the hour (1-59)
Number of seconds
TIMEZONE
Timezone offset from UTC, measured in seconds
N/A
TIMEZONE_HOUR
Hour component of TIMEZONE
N/A
TIMEZONE_MINUTE
Minute component of TIMEZONE
N/A
WEEK
Number of the ISO 8601 week-numbering week of the year
N/A
YEAR
Calendar year
Calendar year
To use the EXTRACT() function for PostgreSQL convert DateTime to date operation, we have listed some examples:
In PostgreSQL format date, to extract a month from a given timestamp,
To extract the year, month, and day from the current timestamp, i.e. using the EXTRACT() function in conjunction with now(),
SELECT
EXTRACT(year FROM now()) as year,
EXTRACT(month FROM now()) as month,
EXTRACT(day FROM now()) as day;
Output:
year | month | day
------+-------+-----
2022 | 6 | 23
(1 row)
In this section of PostgreSQL convert DateTime to Date, we discuss another PostgreSQL function called the DATE_PART(). The DATE_PART() PostgreSQL function is another alternative to the EXTRACT() function, which retrieves date subfields such as year or hour from DateTime. It has similar syntax and takes the same arguments of field and source as specified in the EXTRACT() function.
DATE_PART(field,source)
To illustrate how DATE_PART() function works, here are some examples.
The above-mentioned SQL command extracts ‘year’ from the given timestamp and displays it as the output. To extract the date, month, and year, you can run the following DATE_PART() command.
SELECT DATE_PART('day', TIMESTAMP '2022-05-12 07:37:16') d, DATE_PART('month', TIMESTAMP '2022-05-12 07:37:16') m, DATE_PART('year', TIMESTAMP '2022-05-12 07:37:16') y;
Output:
d | m | y
----+---+------
12 | 5 | 2022
(1 row)
This SQL query runs PostgreSQL DATE_PART() function thrice to get the day (d), month (m), and year (y) from the given timestamp one by one. The DATE_PART() function is inefficient when extracting date parts since you have to run the function thrice within the same query since these three entities cannot be extracted at once.
This guide presented five different ways to perform PostgreSQL convert DateTime to date operation. We learned about the available PostgreSQL functions that can be used to convert a timestamp to date, such as DATE(), TO_CHAR(), EXTRACT(), and DATE_PART(). While some functions, such as TO_CHAR(), can do Postgres convert timestamp to date in less code, other functions, such as DATE_PART(), require extensive writing to perform the job.
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