This is getting NULL, why?
select unix_timestamp(addtime(date(now()), time(from_unixtime(1426705199))))
For some reason, it is running correctly, however it only outputs NULL
I often find, when confronted with an error, that the manual can be a useful resource:
ADDTIME() adds expr2 to expr1 and returns the result. expr1 is a time or datetime expression, and expr2 is a time expression.
You are using a date value for expr1. Try casting it back to datetime expression:
select unix_timestamp(addtime(
timestamp(date(now()))
, time(from_unixtime(1426705199))))
This should work?
SELECT UNIX_TIMESTAMP(NOW())
If you want to get it from your own field then use this..
SELECT UNIX_TIMESTAMP(yourField);
Related
I have the following query:
SELECT
NULLIF(MAX(t.date),'2019-01-15') AS ended
FROM
totals t
This query correctly outputs a date:
> 2019-01-01
But if I reference this query inside of a subquery like so:
SELECT * FROM
(SELECT
NULLIF(MAX(t.date),'2019-01-15') AS ended
FROM
totals t) AS a
This version incorrectly produces a truncated result:
> 201
Can someone help me to understand this behavior and how best to work around it?
Additional Notes:
I am running MySQL version: "5.7.25 MySQL Community Server"
For anyone wanting to test this out, here is an example of a simple test table that is affected by this problem:
CREATE TABLE `totals` (
`date` date NOT NULL,
`value` decimal(10,0) DEFAULT NULL,
PRIMARY KEY (`date`)
);
INSERT INTO `totals` VALUES ('2018-01-01',2000000),('2019-01-01',3000000);
The issue here appears to be a subtle converting/casting issue happening within NULLIF. First, here is a version of your query which does in fact work as expected:
SELECT *
FROM
(
SELECT NULLIF(MAX(t.date), STR_TO_DATE('2019-01-15', '%Y-%m-%d') AS ended
FROM totals t
) AS a
What is happening with your current query is that MySQL is converting the call to MAX(t.date) to text, to match the text literal '2015-01-15'. By ensuring that both arguments to NULLIF are date type, you get the behavior you want.
As for why we are seeing 201 as the string result from the call to NULLIF, I don't have an explanation. But, I can cite the documentation for NULLIF here:
Returns NULL if expr1 = expr2 is true, otherwise returns expr1. This is the same as CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END.
It is a general rule in SQL that both the if and else branches of a CASE expression should always have the same type. Actually, if we violate this rule, in most databases the CASE expression won't even compile. Applying this to NULLIF means that we should always make sure that both arguments have the same type. Breaking from this rule might run on MySQL (similar to doing a non ANSI compliant GROUP BY with full mode turned off), but it is not something we should choose if we can avoid it.
My guess is that there's implicit datatype conversions happening.
As a workaround, I would take the return from the NULLIF function and convert/cast it back to DATE datatype. Simplest would be to wrap it in DATE() function.
SELECT
DATE( NULLIF(MAX(t.date),'2019-01-15') ) AS ended
^^^^^ ^
We could also try converting the string literal, convert that to a DATE, and see if that fixes the problem:
SELECT
NULLIF(MAX(t.date), DATE('2019-01-15') ) AS ended
^^^^^ ^
Or we can do both:
SELECT
DATE( NULLIF(MAX(t.date), DATE('2019-01-15') ) ) AS ended
^^^^^ ^
^^^^^ ^
There are other expressions we can use for the datatype conversion such as CAST(), CONVERT(), or STR_TO_DATE().
Or we could just use the simple + INTERVAL 0 DAY trick. e.g.
SELECT
NULLIF(MAX(t.date),'2019-01-15' + INTERVAL 0 DAY ) + INTERVAL 0 DAY AS ended
^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^
It sounds simple but I'm stuck. What I want is to be able to compare two MySQL DATETIME values but due to the open ended nature of how the queries are formed I do not know the datatype of value 1 or value 2. For instance, each value can either be a string that is input by an end user, a date field or a DATETIME field.
Example:
dateTime1 > 1/18/2017 2:30pm
The issue I'm running into is STR_TO_DATE() expects a string and returns null with DATETIME, DATE_FORMAT() expects a date and returns null with a string. I need a function or nested group of functions that will give me the same result regardless of the value of the datatype & would like to address directly in mysql rather than pre-processing or making the user input validation stricter. I used to use CAST(value, DATETIME), however CAST() doesn't read the date correctly in the more recent versions of MySQL (it ignores the am/pm specification). Any ideas?
GREATEST() did not work for me as it would always return null if any component was null, however it led me to COALESCE() which provides me with the solution I am looking for as it returns the first non NULL value. It makes the assumption the value will always be DATE, DATETIME, or a date time string which is the case for my issue:
SELECT COALESCE(STR_TO_DATE(value1, '%c/%e/%Y %r'), value1) > COALESCE(STR_TO_DATE(value2, '%c/%e/%Y %r'), value2)
Note: value1 and value2 are either DATE / DATETIME columns or date time string values
You can consider using the coalesce() function, with a list of different formats used with str_to_date(). coalesce() will ignore any null from the list (but at least one of them should be non-null, or you still get a null).
select
coalesce(
str_to_date('13/18/2017 2:30pm', '%m/%e/%Y %l:%i%p') -- will get a null
, str_to_date('18/13/2017 2:30pm', '%e/%m/%Y %l:%i%p') -- will get a null
, str_to_date('18/01/2017 14:30', '%e/%m/%Y %k:%i')
) as answer;
The code may be brittle, because there are so many different date/time formats that a human user may input.
You may also need to be very familiar with all the different format characters that str_to_date() take. See this manual page for more details:
https://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_date-format
Updated
An earlier version of this answer incorrectly suggested the use of the greatest() function.
I am facing a silly problem while converting datetime column into y-m-d format.
I am running following query :
SELECT STR_TO_DATE(dateadded, '%y-%m-%d') FROM my_table
Note : The dateadded column is a type of datetime.
Whenever I am running above query it always shows (NULL).
Can somebody solve this issue as this is irritating me ?
Since your column is of datetime type rather than string type you should use DATE_FORMAT function as below:
SELECT DATE_FORMAT(dateadded, '%y-%m-%d')
FROM my_table
This query will work for a four digit year in table
SELECT STR_TO_DATE(dateadded, '%Y-%m-%d')
FROM my_table
while this will work for a two digit year
SELECT STR_TO_DATE(dateadded, '%y-%m-%d')
FROM my_table
you can try this by following query
SELECT
STR_TO_DATE('99-12-12', '%y-%m-%dd'),
STR_TO_DATE('1999-12-12', '%Y-%m-%dd')
both output will be
1999-12-12
for further details
I basically have a table in which the users have inputted their Date of birth in the format.
DAY-MONTH-YEAR (01-Dec-2012)
The data in the table has mixed errors with some people having the that field empty, others have just the words 'DAY-MONTH-YEAR' other having '--', other '' and others just have '02-12-YEAR' and other have '--1985'. I know... terrible
I am trying to now filter so that I only get in my query people that only inputted the full DoB in the correct format.
my REGEXP is not great... and i was wondering if anyone could help me with on how to validate the date in MySQL. I could achieve this easily in PHP but trying to keep this process in the model of my application.
SELECT m_dob FROM `mariners` WHERE m_dob IS NOT NULL AND m_dob != '' and m_dob != 'Day-Month-Year' AND m_dob != '--' AND m_dob REGEXP '^1[() -]*[[:digit:]]{3}[() -]*[[:digit:]]{3}[() -]*[[:digit:]]{4}$';
Save yourself from the pain of using regular expressions and just call upon MySQL's STR_TO_DATE() function instead:
SELECT m_dob FROM mariners WHERE STR_TO_DATE(m_dob, '%d-%b-%Y') IS NOT NULL
As documented in the manual:
If the date, time, or datetime value extracted from str is illegal, STR_TO_DATE() returns NULL and produces a warning.
UPDATE
As noted in your comment, there are some circumstances in which STR_TO_DATE() can return a zero date. To avoid this, either:
enable the NO_ZERO_DATE SQL mode:
SET SESSION sql_mode = 'NO_ZERO_DATE'
or else use another function such as TO_DAYS to verify the date's validity:
SELECT m_dob
FROM mariners
WHERE TO_DAYS(STR_TO_DATE(m_dob, '%d-%b-%Y')) IS NOT NULL
I do not recommend manually trying to capture all instances of input dates that might give rise to a zero date, as it is quite possible that some other corner cases will get overlooked.
I want to implement following logic in my SQL query:
If some date is not set or it's year is 1970 then select real_date flag to null AND change date to current data, else - real_date is true and no need to change date.
real_date is not an actual field in the table but a flag I need to set up.
I can easily do this using 2 lines in my SELECT section:
, IF (actualDate is NULL OR YEAR(actualDate) = 1970, CURRENT_TIMESTAMP(), actualDate) as actual_date
, IF (actualDate is NULL OR YEAR(actualDate) = 1970, null, true) as real_date
And the question - is it the only way to do it? Don't really like the fact that I had to copy condition again. Can somehow the second select be moved to the first one?
Update: I need to select both actualDate (it will be either fixed to current time version or the actual stored value) and real_date (which will be true or false/null). Maybe I am missing something, but how could COALESCE function help here?
Update 2: Thanks again everyone. Learnt other ways to write it but all of them have check in 2 places. My idea was to have logical condition in only one place but doesn't seem to be possible.
Your variant is pretty and comfortable for supporting code in future, do not change anything.
You can use the COALESCE function.
Returns the first non-NULL value in the list, or NULL if there are no non-NULL values.
You can also use CASE WHEN ... THEN ... END (with multiple WHEN) instead of the two IF
`
Check this here : http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html
But the COALESCE function can do the job for this case.
I might try something like this instead:
…
, COALESCE(NULLIF(actualDate, '1970-01-01'), CURRENT_TIMESTAMP()) AS actual_date
, NULLIF(actualDate <> '1970-01-01', false) AS is_real_date
…
Or maybe the second NULLIF() is not really necessary? Consider this:
…
, COALESCE(NULLIF(actualDate, '1970-01-01'), CURRENT_TIMESTAMP()) AS actual_date
, (actualDate <> '1970-01-01') AS is_real_date
…
The second column could then be true, false or NULL, and you could treat NULL same as false.
This is the most compact form I can think of using COALESCE and without repeating any comparison:
select id, type, real_date, if(real_date, actual_date, now()) as actual_date
from (
select *, coalesce(year(actual_date), 1970) != 1970 as real_date from table1
) as subResult
Working example