What is wrong here? I want to change format of date and then order it (I use MySQL):
SELECT * FROM changes ORDER BY DATE_FORMAT(`when`,'%e %c'), `class`, `hour` ASC
I want to change format of date and then order it
Probably not. You probably want to order by date. It's not clear whether you want to include the formatted date in your SELECT clause, but I'll assume you do.
SELECT *, DATE_FORMAT(`when`,'%e %c') as formatted_date
FROM changes
ORDER BY `when`, `class`, `hour` ASC
You will find that date_format(%e %c) will be converting a numeric field (in this case month and day) into a varchar, but will not be including leading 0s. This is going to cause issues in sorting as %c will convert September to 9 and October to 10, which will mean September will actually appear as a later date (the first character, 9, is greater than 1). This is also the same problem with %e as the 3rd of the month will appear after the 20th etc.
Easiest answer is not converting your dates into a varchar and allowing the sorting to function as a date, or prepending leading 0s to both the day and the month. In your comment you say you wish to sort "by the months and then days" and "my dates are always in the same year". A normal date would be sorted by year/month/day, so assuming the years are the same (which you say), and then you wish to sort by the month and then days, a normal date sort should suffice without any conversion. If this is not the sort order you require, perhaps you need to clarify, or provide some example data with what you want to see.
If for some reason you do want to sort by day and then by month (1 January, 1 February... 2 January, 2 February ...) you could use date_format(%d %m) which is the same as your original code, except will include leading 0s and enable a sort to function correctly.
Related
I want to get the previous month date for specific dates in SQL. For example: 6.21.19 has a previous month date of 5.21.19.
I am just trying to get comps from this.
MONTH( curdate() ) -1
I need to return the previous month date.
Welcome to the board Arie. Judging from your question and responses, you need a range of dates and their prior month relations. The easiest way would be for all of the dates you need to look up to be in a table, then the answers provided so far would work. Since that doesn't appear to be the case, I'm guessing you are creating date ranges on the fly.
So lets assume you need exactly the data shown in your example, there are two parts to this, first you need to get a list of days that you want to look up, then you need to get the day in the prior month. There are lots of ways to get a sequence of days, but for simplicity I'll use a recursive CTE. Once I have the date range, I'll just select the dates and their prior month date as well.
with Date_CTE as (select cast('6/1/2019' as datetime) as repDate
union all
select dateadd(day, 1, repdate) as repDate
from Date_CTE
where repDate < '06/07/2019')
select repDate, dateadd(month, -1, repDate) as PriorDate
from Date_CTE
CTEs are helpful functions and you can get more details on them here, but it's worth noting there are many ways to do this. Hope this gets you pointed in the right direction.
SELECT yourDateColumn, yourDateColumn-interval 1 month as prevMonthDate
SELECT * FROM table WHERE '2016-03-31' > (SELECT MAX(year) from table where bill_id = 'somevalue')
I am using above query to check if 2016-03-31 is greater than all years present in table against bill_id. It is working fine. but is it correct approach to compare dates. dates will always in above format. Is there any need to convert date format for comparison. value 2016-03-31 will change dynamically but it will be always in Y-m-d format
Note : year is column name which contains full date in Y-m-d format like 2016-05-20
You are not comparing dates. You are comparing a string '2016-03-31' with a number, e.g. 2015.
In order to compare, MySQL silently converts the string to number. One would expect this to crash, as '2016-03-31' certainly isn't a number. MySQL, however, reads from left to right and takes from there all that can be considered a number, i.e. '2016'. Well, one could argue that some people put a minus sign at the end of a number, so this should be '2016-', i.e. -2016. Anyway, MySQL stops before the minus sign, gets 2016 and uses this for the comparision.
I don't know if all this is guaranteed to work in the future. I would not rely on this.
What result would you expect anyway? Is the 31st of March 2016 greater than the year 2016? That's a queer question, don't you think?
Try this. But do you really have a column year that stores only year?
SELECT * FROM table WHERE year(STR_TO_DATE('2016-03-31'))
> (SELECT MAX(year) from table where bill_id = 'somevalue')
SELECT * FROM table WHERE YEAR('2016-03-31') > (SELECT MAX(year) from table where bill_id = 'somevalue')
MySQL YEAR() returns the year for a given date or timestamp. The return value is in the range of 1000 to 9999 or 0 for 'zero' date.
So I have to store a particular date of the year, any year. So I will only be needing the date and month part of a date.
I can either store it with any year and just ignore it on the programming side but that feels dirty. Any better way to handle this?
Closest I could find was this one but that includes time component as well and goes on some different tangent.
If you're using MySQL >= 5.7.6, you could use a generated column. A trivial example table would look like this (untested as, ironically, I don't have access to a recent MySQL server right now):
CREATE TABLE myTable (
the_date DATE,
month_date VARCHAR(5) AS CONCAT(MONTH(the_date), '-', DAY(the_date))
);
Of course, change the generated value according to your needs (different separator, padding with zeroes on the month, etc.)
If you're stuck with an older version, you could perform a similar conversion using a view.
What is wrong with just having a DATE column value, in this example called my_date :
SELECT MONTH(my_date) AS myMonth, DAY(my_date) AS myDay, <othercolumns>
FROM table WHERE id = 1
Then you can use your PHP to get your row and output $row['myMonth'], etc.
You can also output the MONTH / DAY values as any format string you like using MySQL DATE_FORMAT .
You can also CONCAT these two values if you need them in a single column.
SELECT CONCAT(MONTH(my_date),' ',DAY(my_date)) as month_day, <othercolumns>
FROM table WHERE id = 1
Warning:
Storing dates as 0000-00-00 is perfectly valid but MySQL year 0000 is not a leap year so you can not store 0000-02-29, this will instead be saved as a default 0000-00-00.
You might as well use a default year value that is leap year safe (such as year 2k) if you're sure you're never going to use the year value. such as (2000-XX-XX).
You could store the Julian Date as an integer, and convert to Georgian Month/Day when you need it. This can keep things quite clean. Keep your eyes peeled for the leap year.
The notion of Julian here is truly, just "Day of year" and converting when needed.
function getDateFromDay($dayOfYear, $year) {
$date = DateTime::createFromFormat('z Y', strval($dayOfYear) . ' ' . strval($year));
return $date;
}
I want to show date column in DESC order where date is entered as VARCHAR and is in order 20-JUN-2007 I have already used ORDER BY RIGHT(vPublishedDate, 4) but it doesn't effect the month and date
Here is one way to do it using STR_TO_DATE (take into account the other answers about converting the column to date, although you may not have control over the database):
SELECT ...
FROM ...
ORDER BY STR_TO_DATE(vPublishedDate,'%d-%M-%Y')
As an example:
SELECT STR_TO_DATE('20-JUN-2007','%d-%M-%Y') as Date;
+------------+
| Date |
+------------+
| 2007-06-20 |
+------------+
Why are you using a VARCHAR to store a DATE? Use a DATE to store a DATE and then, as if by magic, sorting works all on its own.
You really should be storing dates as dates, not character-type fields. Then you wouldn't need to worry about this sort of "SQL gymnastics" (as I like to call it).
Databases are for storing data, not formatting.
By forcing yourself to manipulate sub-columns, you basically prevent the database from performing any useful optimisations.
In order to do what you want with the data you have you have to do something like:
use substring to extract individual sub-column information to get them in the order you want; and
use some sort of lookup to turn a string like "NOV" into 11 (since the month names will sort as DEC, FEB, AUG, APR, JAN, JUL, JUN, MAR, MAY, NOV, OCT, SEP).
And this would be a serious performance killer. Now there may be a function which can turn that particular date format into a proper date but I urge you: don't use it.
Set up or change your database to use an intelligent schema and all these problems will magically disappear.
It's a lot easier to turn a date column into any sort of output format than to do the same with a character column.
Change that VARCHARto a Date type column, if you can.
You can also try this, although this is NOT the RIGHT approach.
Select STR_TO_DATE(your_date_column,'%d/%m/%Y') AS your_new_date from your_table order by your_new_date DESC
Try converting the varchar to date using str_to_date and then you can apply the sorting logic.
I would suggest you to change the type as Date.
Then run a script which converts your dates to the correct DB format.
Sorting would be then be just as simple as sorting ids in MySql
I want to order by date.
e.g.
table_date
February 2011
January 2011
December 2010
I've already tried:
SELECT distinct(table_date) FROM tables ORDER BY table_date DESC
bur it doesn't work.
I get this instead:
January 2011
February 2011
December 2010
Can you help me please?
If you must store the dates in a varchar which as others pointed out is not recommended, you could use:
SELECT table_date FROM tables ORDER BY STR_TO_DATE(table_date, '%M %Y') DESC;
If you want to order by date, store it as a date, not a string. Unless your date string is of the form yyyy-mm-dd, it will not sort as you want it.
Databases are hard enough work as-is, without people making it harder, and you should be striving as much as possible to avoid what I like to call SQL gymnastics.
Store it as a date then, if you must, use date functions to get it in the form February 2011.
It'll be a lot easier going that way than what you're trying to do.
Even if you can't change any of the current columns due to code restrictions, you can always add another column to the database like TABLE_DATE_AS_DATE and put in an insert/update trigger to populate it based on TABLE-DATE.
Then just do:
update table x set table_date = table_date
or something similar, to fire the trigger for all rows.
Then, your query can still get at table_date but use table_date_as_date for ordering. That's a kludge of course but I've had to use tricks like that in the past when it was imperative the code could not change, so we had to resort to DBMS trickery.
Store dates as DATE, not as VARCHAR, that's a huge mistake. Use STR_TO_DATE() to convert your content. When you're done, you can order by dates without any problems.
Date should be stored as date and not VARCHAR.
Suppose you have table_date in the following format (DD-MM-YYYY)
table_date
2011-01-01
2011-02-01
2010-12-01
Now you can perform order by clause in the following way
SELECT * FROM table_order ORDER BY str_to_date(date, "%Y-%M-%D") ASC
I doubt if the output will be in ordered form