List top ten each month in sql postgresql
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Dates in a database aren’t stored as strings, but we input and fetch data from it as if it were a string with the following format for the information: Show where the letters stand for Year, Month, Day, Hour, Minutes and Seconds. Let’s say for example that we want to record that we got a new user on April 10, 2023 at exactly 10:39. To represent that exact date and time we would use the format: 7 TODO: this format is also supported: January 8 04:05:06 1999 PST To get some familiarity try creating and SELECTing a few TIMESTAMPS below. I was born on May 1st, 1983 at exactly 4:00am. Can you fetch that timestamp? We’re just going to jump in here. We need to use a different table as none of the previous ones we’ve been using have had date fields in them. Another table available to us in chinook is employees. Let’s get familiar with what columns are in this table by looking at the first few rows. Note that there are several columns so you may have to scroll right to see all of the data: Each employee has two TIMESTAMP columns, one for their birth_date and one for their hire_date. You can use all of the ORDERing, GROUPing and other functions we learned for other columns on DATE columns as well. Try getting a list of the 4 youngest employees in the company. Formatting Dates to stringsOften you don’t want to show the full raw TIMESTAMP, but rather a nicely formatted, potentially truncated version. For example, let’s say we want to get a list of the employees names and the year that they were hired. To do so we’ll need to parse the hired_date to just pull out the year. We can do so with the TO_CHAR function which works as follows where [date type] is a column or value of any of the above listed date/time data types, and [pattern] is a string indicating how to format the output date. The main symbols you’ll want to use to create your format patterns are here PATTERNDESCRIPTIONEXAMPLEOUTPUTHH DESCRIPTION Hour (01-12) EXAMPLE 8 OUTPUT 04 HH24 DESCRIPTION Hour (01-24) EXAMPLE 9 OUTPUT 16 MI DESCRIPTION Minute EXAMPLE 0 OUTPUT 15 SS DESCRIPTION Seconds EXAMPLE 1 OUTPUT 23 am DESCRIPTION displays whether time is am or pm EXAMPLE 2 OUTPUT am YY DESCRIPTION last 2 digits of the Year EXAMPLE 3 OUTPUT 23 YYYY DESCRIPTION 4 digits of the Year EXAMPLE 4 OUTPUT 2023 MM DESCRIPTION Month # of the year EXAMPLE 5 OUTPUT 04 Month DESCRIPTION written Month of the year capitalized EXAMPLE 6 OUTPUT April Mon DESCRIPTION abbreviated of Month of year EXAMPLE 7 OUTPUT Apr DD DESCRIPTION Day # of the month EXAMPLE 8 OUTPUT 10 Day DESCRIPTION written Day of the week EXAMPLE 9 OUTPUT Monday Dy DESCRIPTION abbreviated Day of the week EXAMPLE 0 OUTPUT Mon WW DESCRIPTION Week # of the year EXAMPLE 1 OUTPUT 15 Q DESCRIPTION Quarter of the year EXAMPLE 2 OUTPUT 2 TZ DESCRIPTION TimeZone EXAMPLE 3 OUTPUT UTC The above patterns can be string together to get the format you eventually want. Some common outputs are: and and You don’t have to memorize these (it’s hard to!). It’s just good to get familiar with how it works and then reference back to it when you need it in the future. Number formattingThere are a couple of extra tools you can use on patterns that output numbers. FORMATTERDESCRIPTIONEXAMPLEOUTPUTFM DESCRIPTION Fill Mode will remove any 0’sat the front of a 2 digit number. EXAMPLE 4 OUTPUT 5 th DESCRIPTION adds the ordinal suffixeslike st, nd or th to the end of a number EXAMPLE 4 OUTPUT 05th And of course you can combine the two to get String FormattingFor string outputs, most of the patterns above support different casing output based on the case you use for the pattern. Some examples using different casings of “Day”: And you can see the following common date format in UPPERCASE, Capitalized and lowercase formats: Note that the case for numeric values doesn’t change. Still use DD for the day # of the month and YYYY for year. We’re going to move on in the tutorial but if you’d like more details checkout the full list of PostgreSQL date formatting functions. Current DATE and TIME FunctionsPostgreSQL supports a number of special values, or functions to help bet the current DATE, TIMESTAMP or TIME. The most used ones are and they are used by just putting them in the query 0 GROUPing BY DATEIn analytic queries, it’s very common to group things by dates. For example you may want to see new users by year, month, week or day. To do so, you’ll want to use the TO_CHAR function to convert the dates into a truncated string before you GROUP BY it. You don’t want to simply GROUP BY the raw date as those are accurate down to the millisecond so grouping by the unaltered date would be like making GROUPs for each millisecond. The following examples are using the hire_date field from the employees table and show a lot of common formats you can use for these groups. These are what we use at Chartio for our date group formatting standards. GROUP PERIODEXAMPLE SQLEXAMPLE OUTPUTSECOND EXAMPLE SQL 6 EXAMPLE OUTPUT 2018-03-04T00:00:00 Minute EXAMPLE SQL 7 EXAMPLE OUTPUT 2018-08-14T00:00 Hour EXAMPLE SQL 8 EXAMPLE OUTPUT 2018-01-02T00 Day EXAMPLE SQL 9 EXAMPLE OUTPUT 2003-10-17 Week EXAMPLE SQL 0 EXAMPLE OUTPUT 2002-W33 Month EXAMPLE SQL 1 EXAMPLE OUTPUT 2002-05 Quarter EXAMPLE SQL 2 EXAMPLE OUTPUT 2003-Q2 Year EXAMPLE SQL 3 EXAMPLE OUTPUT Y2012 Hour of Day EXAMPLE SQL 4 EXAMPLE OUTPUT 14 Day of Week EXAMPLE SQL 5 EXAMPLE OUTPUT Thursday Day of Month EXAMPLE SQL 6 EXAMPLE OUTPUT 17 Day of Year EXAMPLE SQL 7 EXAMPLE OUTPUT 125 Month of Year EXAMPLE SQL 8 EXAMPLE OUTPUT October Feel free to try out any of the above formats on the query below: 1 There are only 8 employees in our database so we’re not dealing with too many groups there. You can get a little more granular with the invoices table and it’s invoice_date column with 250 rows. 2 The above query returns the number of invoices created per year. Can you modify it to get a SUM of the total amount invoiced by month? How to get top 10 values in PostgreSQL?Postgres does have a way to select the top N rows from an SQL query, but the syntax does not use the top keyword. Instead, the limit keyword must be used. PostgreSQL also gives the ability to limit the number of rows with an offset from the first row. That can be achieved using the limit N offset Y syntax. How to get data for each month in SQL?You usually want to take into account both the year and the month of the date, i.e. you want to group events in January 2022 separately from events in January 2021. To group data by month in SQL Server, use the DATEPART() function. It extracts the given part (year, month, etc.) from the date. How to get data of specific month in PostgreSQL?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 BY clause to group the results by month. This blog will show you how to group the table's data by month in Postgres. How to count records by month in PostgreSQL?Similarly, to group data by month, you can use the DATE_TRUNC function with 'month' as the first argument. For example: SELECT DATE_TRUNC('month', date) AS month, SUM(quantity) FROM sales GROUP BY month; This query will return a list of months along with the total quantity sold each month. |
