I have several things which I want to discuss with you guys.
Since, they were just simple questions, so no dataset here.
Suppose I have a datetime type column which called started_date, the value in it was like:
yyyy-mm-dd hh:mm:ss. So, if I want to select some IDs which were larger than one specified day (let's say June/01/2017), can I just using
select ID, started_date
from table1
where started_date>"2017-06-01";
Does this work?
I tried some samples, and it worked indeed in the mysql. However, someone told me that I cannot compare the datetime column with string values without converting their format. And it confused me. Because I thought the value "2017-06-01" here was date type value, so it does not need convert. Or am I thinking wrong?
Another thing was about the double quote and single quote, I understand that the single quote was used for string values. However, in this case, when I used double quote to quote "2017-06-01", it works. So, does it mean the double quote can quote date values?
I am just asking, so any response is welcome.
Thanks.
Your query is fine. You are using a safe date/time format for the string. In other words, if you have to store the value as a string, then use that format.
I would write the code as:
where started_date >= '2017-06-01'
I see no reason to exclude midnight on 2017-06-01 (although you might have a reason). Second, single quotes are the standard delimiter for strings.
That said, you can store the value as a string.
As a best practice, I stay away from comparing time-stamps to date-stamps. In this case you can be explicit and truncate the start date. And yes, use single quotes instead.
where SUBSTR(started_date, 1, 10) > '2017-06-01'
To make sure it works you could just convert the date time to a string first and compare the two strings:
to_char(started_date,'YYYY-MM-DD') >= '2017-06-01'
The Strings will compare just fine in that format.
Related
I'm using a varchar field to store a time notation (format: 00:00).
How'd I sort results on this field, so that eg 08:00 comes before 10:00?
Thanks for your support.
Ideally you should be storing the data as TIME but you can always CAST the date time literals on-demand:
ORDER BY CAST(thetime AS TIME)
Use TIME_FORMAT function in your ORDER BY clause
assuming your column is named thetime and is always expressed as 24-hours format hours:minutes (23:43)
ORDER BY TIME_FORMAT(thetime, '%H:%i');
You don't have an issue. '08:00' is less than '10:00'.
You don't have the problem because you have zero-padded the string. This works for up to '99:59'. If you need three-digit hours, then you need to store an addition 0 for the hour: '008:00'' and'010:00'`.
Of course, you can also use a TIME data type. That would generally make sense, but it is limited in its range and it stores sub-minute parts for the time (so under some circumstances, it might not be a perfect fit for your needs).
We have a field in a query that should be left-padded with zeroes if it is too short, and we accomplish this using the Format() function. However, there are some values that produce bizarre results.
Format("14425112-8","00000000-00")
Returns the value "00019330-78"
For most inputs, the string gets formatted as expected, 8 digits, hyphen, two digits. But in a few rare cases, the value is modified. Is this repeatable for anyone else? Does anyone have an explanation?
Thanks for your help.
This is an example of access trying to be too helpful. It looks like it is interpreting these values as dates, but since you didn't use any date indicators in the format e.g: (dd,mm,yyyy), it converted 1-1 to a date, and then tried to display it in decimal form:
debug.print Format("1-1","000000-00")
returns 000427-36 which is the decimal value 42736 which, if you convert to a date, becomes 1/1/2017. This is what access interpreted "1-1" as.
it seems that access has reserved the - character as symbolizing a date format, despite what their website says. This function is only useful for formatting actual dates, or numeric values, such as prices. If you are set on using the format function, you will have to change you separator to a decimal point, which apparently is the only character that will get you what you want with the leading and trailing zeros.
Otherwise, you may have to build your own function for this.
You cannot format a string like a number this way. Try this:
PaddedNumber = Right(String(8, "0") & "14425112-8", 10)
I am doing a series of updates on some tables after I import them from tab-separated values. The data comes with dates in a format I do not like. I bring them in as strings, manipulate them so that they are in the same format as MySQL dates and then convert the column. Or sometimes not, but I want them to be like MySQL dates even if they are strings.
They start out like '1/4/2013 12:00:00 AM' or '11/4/2012 2:37:45 PM'.
I turn these into '2013-01-04' (usually, since times are present even when the original schema clearly specifies dates only) and '2012-11-04 14:37:45'.
I am using rlike. And this does not use indexes? Wow. That sucks.
But already, for each column, I have to use 4 updates to handle the different cases ('1/7', '2/13', '11/2', '12/24'). If I did these using like, it might take 16 different updates for each column....
And, if I am seeing it right, I cannot even get positional parameters out of the rlike expression, yes? You know, the part of the expression wrapped in parentheses that becomes $1 or $2....
So, it seems as though it is going to be quicker to pre-process the tsv file with perl. Really? Wow. Again, this sucks.
Any other suggestions? I cannot have this taking 3 hours every time I need to pull in the data.
Recall the classic 1997 quote from Jamie Zawinski:
Some people, when confronted with a problem, think "I know, I'll use regular expressions."
Now they have two problems.
Have you tried using STR_TO_DATE()? This is exactly for parsing nonstandard date/time strings into canonical datetime values.
If you try parsing with STR_TO_DATE() and the string doesn't match the expected format, the function returns NULL.
So you could try parsing in different formats, and return the first one that gives a non-null result.
UPDATE mytable
SET datecolumn = COALESCE(
STR_TO_DATE(stringcolumn, '%m/%d'),
STR_TO_DATE(stringcolumn, '%d/%m/%Y'),
...etc.
);
I can't tell what your different cases are. It might or might not be possible to cover all cases in one pass.
Another alternative is as you say, preprocess the raw data with Perl before you load it into MySQL. But even then, don't fight with regular expressions, use Date::Parse instead.
The main problem is, that I have stored in database datetime , not the date (what I need). Ok never mind.
I have thousands of reports stored each day.
I need to LEFT by 10 my datetime_view (to cut the time) and everything's fine. Except this. I'm trying to figure out why do I have to put in the condition + one day from the future? Otherwise it won't search what I want.
SELECT
LEFT(datetime_view,10),
count(type)
FROM reports
WHERE
type IN (1,2,5)
AND
datetime_view>='2012-10-28'
AND
datetime_view<='2012-11-04'
group by LEFT(datetime_view,10);
You can see I must search from the future. Why??
It gives me an output from 28.10 to 3.11 ....
don't use string operations on date/time values. MySQL has a huge set of functions for date/time manipulation. Try
GROUP BY DATE(datetime_view)
instead, which will extract only the date portion of the datetime field. Your string operation is not y10k compliant. Using the date() function is.
As for your plus one day, consider how the comparisons are done: A plain date value, when used in date/time comparisons, has an implicit 00:00:00 time value attached to it, e.g. all dates have a time of "midnight".
i think it's better to use DATE(datetime_view) to cut the time instead of LEFT(datetime_view,10), also on the where condition:
DATE(datetime_view) <= '2012-11-03'
I am fetching the current date & time using NOW() in mysql. I want to convert the date value into a varchar and concat it with another string. How do I do it?
Use DATE_FORMAT()
SELECT
DATE_FORMAT(NOW(), '%d %m %Y') AS your_date;
This is super old, but I figured I'd add my 2c. DATE_FORMAT does indeed return a string, but I was looking for the CAST function, in the situation that I already had a datetime string in the database and needed to pattern match against it:
http://dev.mysql.com/doc/refman/5.0/en/cast-functions.html
In this case, you'd use:
CAST(date_value AS char)
This answers a slightly different question, but the question title seems ambiguous enough that this might help someone searching.
Try this:
concat(left(datefield,10),left(timefield,8))
10 char on date field based on full date yyyy-MM-dd.
8 char on time field based on full time hh:mm:ss.
It depends on the format you want it. normally you can use script above and you can concat another field or string as you want it.
Because actually date and time field tread as string if you read it. But of course you will got error while update or insert it.