SQLite only understands certain fundamental data types, and neither Date nor 
POSIXct types are among them. They get stored as their internal numeric 
representations. 

The internal numeric representations of Date and POSIXct are incompatible. You 
are sending Dates to SQLite and trying to then interpret it as POSIXct by 
handing that numeric to strftime.

Note that within R the Date and POSIXct types are made sort-of compatible by 
internal checking of class attributes that are not stored in SQLite. They are 
still only sort-of compatible because Date has no concept of time zone and 
always assumes GMT rather than local time when being converted.

I recommend retrieving the stored Date value as a Date value into R so that 
strftime can recognize how to interpret it. If you need to handle time as well 
as date you may find that converting to character first before converting to 
POSIXct with an appropriate time zone behaves with least surprises. 
-- 
Sent from my phone. Please excuse my brevity.

On September 16, 2016 6:23:48 AM PDT, PIKAL Petr <petr.pi...@precheza.cz> wrote:
>Hi Peter
>
>The devil is in detail
>
>Data from OP had different format and was transferred to Date object by
>as.Date, which results in incorrect values (and NA if not transferred)
>df <- data.frame(Date =
>c("2013/05/25","2013/05/28","2013/05/31","2013/06/01","2013/06/02",
>"2013/06/05","2013/06/07"), Quantity = c(9,1,15,4,5,17,18))
>df$Date<-as.Date(df$Date)
>cbind(df, sqldf("select strftime( '%m', Date) from df"))
>
>Data formatted according to your example transferred to Date object by
>as data, again incorrect result
>df2 <- data.frame(Date =
>c("2013-05-25","2013-05-28","2013-05-31","2013-06-01","2013-06-02",
>"2013-06-05","2013-06-07"), Quantity = c(9,1,15,4,5,17,18))
>df2$Date<-as.Date(df2$Date)
>cbind(df2, sqldf("select strftime( '%m', Date) from df2"))
>
>Data formatted according to your example but **not** changed to Dates,
>correct result
>df3 <- data.frame(Date =
>c("2013-05-25","2013-05-28","2013-05-31","2013-06-01","2013-06-02",
>"2013-06-05","2013-06-07"), Quantity = c(9,1,15,4,5,17,18))
>cbind(df3, sqldf("select strftime( '%m', Date) from df3"))
>
>so sqldf is a bit peculiar about required input values and does not
>know how to handle Date objects.
>
>Cheers
>Petr
>
>
>> -----Original Message-----
>> From: peter dalgaard [mailto:pda...@gmail.com]
>> Sent: Friday, September 16, 2016 2:45 PM
>> To: PIKAL Petr <petr.pi...@precheza.cz>
>> Cc: Manohar Reddy <manu.redd...@gmail.com>; R-help <r-help@r-
>> project.org>
>> Subject: Re: [R] stfrtime function not returning proper results
>through sqldf
>> package in R
>>
>> Presumably, sqldf does not know about Date object so passes an
>integer that
>> gets interpreted as who knows what...
>>
>> This seems to work:
>>
>> > df <- data.frame(date=as.character(Sys.Date()+seq(0,180,,10)))
>> > cbind(df, sqldf("select strftime( '%m', date) from df"))
>>          date strftime( '%m', date)
>> 1  2016-09-16                    09
>> 2  2016-10-06                    10
>> 3  2016-10-26                    10
>> 4  2016-11-15                    11
>> 5  2016-12-05                    12
>> 6  2016-12-25                    12
>> 7  2017-01-14                    01
>> 8  2017-02-03                    02
>> 9  2017-02-23                    02
>> 10 2017-03-15                    03
>>
>> -pd
>>
>>
>>
>> On 16 Sep 2016, at 13:48 , PIKAL Petr <petr.pi...@precheza.cz> wrote:
>>
>> > Hi
>> >
>> > Most probably there is some syntactic suger how to correctly
>formulate sql
>> query.
>> >
>> >> sqldf('select Date, strftime("Date", "%m") from log')
>> >        Date strftime("Date", "%m")
>> > 1 2013-05-25                   <NA>
>> > 2 2013-05-28                   <NA>
>> > 3 2013-05-31                   <NA>
>> > 4 2013-06-01                   <NA>
>> > 5 2013-06-02                   <NA>
>> > 6 2013-06-05                   <NA>
>> > 7 2013-06-07                   <NA>
>> >> sqldf('select Date, format("Date", "%m") from log')
>> > Error in sqliteSendQuery(con, statement, bind.data) :
>> >  error in statement: no such function: format
>> >>
>> >
>> > format(sqldf("select Date from log"), "%m")
>> >
>> > This one however works.
>> >
>> > Cheers
>> > Petr
>> >
>> > From: Manohar Reddy [mailto:manu.redd...@gmail.com]
>> > Sent: Friday, September 16, 2016 11:55 AM
>> > To: PIKAL Petr <petr.pi...@precheza.cz>
>> > Cc: R-help <r-help@r-project.org>
>> > Subject: Re: [R] stfrtime function not returning proper results
>> > through sqldf package in R
>> >
>> >
>> > Hi Petr,
>> >
>> > Thanks, For me also it’s working fine when I directly used that
>function  but
>> when I call strftime function through sqldf package it’s returning NA
>values
>> (PFA) ,but my requirement is I need to do that only sqldf as I’m
>writing some
>> “T sql ” queries against on the dataset.
>> >
>> > Manu.
>> >
>> > On Fri, Sep 16, 2016 at 12:56 PM, PIKAL Petr
>> <petr.pi...@precheza.cz<mailto:petr.pi...@precheza.cz>> wrote:
>> > Hi
>> >
>> > Hm
>> >> format(log$Date, "%m")
>> > [1] "05" "05" "05" "06" "06" "06" "06"
>> >> strftime(log$Date, "%m")
>> > [1] "05" "05" "05" "06" "06" "06" "06"
>> >>
>> >
>> > works for me.
>> >
>> > Just a blind guess, is an object date somwhere in your environment?
>> >
>> > Cheers
>> > Petr
>> >
>> >
>> >> -----Original Message-----
>> >> From: R-help
>> >>
>[mailto:r-help-boun...@r-project.org<mailto:r-help-bounces@r-project.
>> >> org>] On Behalf Of Manohar Reddy
>> >> Sent: Friday, September 16, 2016 6:36 AM
>> >> To: R-help <r-help@r-project.org<mailto:r-help@r-project.org>>
>> >> Subject: [R] stfrtime function not returning proper results
>through
>> >> sqldf package in R
>> >>
>> >> Hi ,
>> >>
>> >>
>> >>
>> >>  I have data something looks like below (or PFA), but when I’m
>> >> extracting month  using *strftime*  function through *sqldf*
>library
>> >> ,it’s returning below results but it’s not returning exact results
>> >> ,it supposed to return 05,05,05,06,06,06.Can anyone please guide
>me
>> >> how to do that with
>> >> *strftime* function.
>> >>
>> >>
>> >>
>> >> Thanks in advance.
>> >>
>> >>
>> >>
>> >> Quiries :
>> >>
>> >>
>> >> library(scales)
>> >>
>> >> # load data:
>> >> log <- data.frame(Date =
>> >>
>c("2013/05/25","2013/05/28","2013/05/31","2013/06/01","2013/06/02","2
>> >> 013
>> >> /06/05","2013/06/07"),
>> >>  Quantity = c(9,1,15,4,5,17,18))
>> >>
>> >>
>> >> # convert date variable from factor to date format:
>> >> log$Date <- as.Date(log$Date,
>> >>  "%Y/%m/%d") # tabulate all the options here
>> >> str(log)
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> Manu.
>> >
>> > ________________________________
>> > Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a
>jsou
>> určeny pouze jeho adresátům.
>> > Jestliže jste obdržel(a) tento e-mail omylem, informujte laskavě
>> neprodleně jeho odesílatele. Obsah tohoto emailu i s přílohami a jeho
>kopie
>> vymažte ze svého systému.
>> > Nejste-li zamýšleným adresátem tohoto emailu, nejste oprávněni
>tento
>> email jakkoliv užívat, rozšiřovat, kopírovat či zveřejňovat.
>> > Odesílatel e-mailu neodpovídá za eventuální škodu způsobenou
>> modifikacemi či zpožděním přenosu e-mailu.
>> >
>> > V případě, že je tento e-mail součástí obchodního jednání:
>> > - vyhrazuje si odesílatel právo ukončit kdykoliv jednání o uzavření
>smlouvy,
>> a to z jakéhokoliv důvodu i bez uvedení důvodu.
>> > - a obsahuje-li nabídku, je adresát oprávněn nabídku bezodkladně
>> přijmout; Odesílatel tohoto e-mailu (nabídky) vylučuje přijetí
>nabídky ze
>> strany příjemce s dodatkem či odchylkou.
>> > - trvá odesílatel na tom, že příslušná smlouva je uzavřena teprve
>výslovným
>> dosažením shody na všech jejích náležitostech.
>> > - odesílatel tohoto emailu informuje, že není oprávněn uzavírat za
>> společnost žádné smlouvy s výjimkou případů, kdy k tomu byl písemně
>> zmocněn nebo písemně pověřen a takové pověření nebo plná moc byly
>> adresátovi tohoto emailu případně osobě, kterou adresát zastupuje,
>> předloženy nebo jejich existence je adresátovi či osobě jím
>zastoupené
>> známá.
>> >
>> > This e-mail and any documents attached to it may be confidential
>and are
>> intended only for its intended recipients.
>> > If you received this e-mail by mistake, please immediately inform
>its
>> sender. Delete the contents of this e-mail with all attachments and
>its copies
>> from your system.
>> > If you are not the intended recipient of this e-mail, you are not
>authorized
>> to use, disseminate, copy or disclose this e-mail in any manner.
>> > The sender of this e-mail shall not be liable for any possible
>damage caused
>> by modifications of the e-mail or by delay with transfer of the
>email.
>> >
>> > In case that this e-mail forms part of business dealings:
>> > - the sender reserves the right to end negotiations about entering
>into a
>> contract in any time, for any reason, and without stating any
>reasoning.
>> > - if the e-mail contains an offer, the recipient is entitled to
>immediately
>> accept such offer; The sender of this e-mail (offer) excludes any
>acceptance
>> of the offer on the part of the recipient containing any amendment or
>> variation.
>> > - the sender insists on that the respective contract is concluded
>only upon
>> an express mutual agreement on all its aspects.
>> > - the sender of this e-mail informs that he/she is not authorized
>to enter
>> into any contracts on behalf of the company except for cases in which
>he/she
>> is expressly authorized to do so in writing, and such authorization
>or power of
>> attorney is submitted to the recipient or the person represented by
>the
>> recipient, or the existence of such authorization is known to the
>recipient of
>> the person represented by the recipient.
>> >
>> >
>> >
>> > --
>> >
>> >
>> > Thanks,
>> > Manohar Reddy P
>> > +91-9705302062.
>> >
>> > ________________________________
>> > Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a
>jsou
>> určeny pouze jeho adresátům.
>> > Jestliže jste obdržel(a) tento e-mail omylem, informujte laskavě
>> neprodleně jeho odesílatele. Obsah tohoto emailu i s přílohami a jeho
>kopie
>> vymažte ze svého systému.
>> > Nejste-li zamýšleným adresátem tohoto emailu, nejste oprávněni
>tento
>> email jakkoliv užívat, rozšiřovat, kopírovat či zveřejňovat.
>> > Odesílatel e-mailu neodpovídá za eventuální škodu způsobenou
>> modifikacemi či zpožděním přenosu e-mailu.
>> >
>> > V případě, že je tento e-mail součástí obchodního jednání:
>> > - vyhrazuje si odesílatel právo ukončit kdykoliv jednání o uzavření
>smlouvy,
>> a to z jakéhokoliv důvodu i bez uvedení důvodu.
>> > - a obsahuje-li nabídku, je adresát oprávněn nabídku bezodkladně
>> přijmout; Odesílatel tohoto e-mailu (nabídky) vylučuje přijetí
>nabídky ze
>> strany příjemce s dodatkem či odchylkou.
>> > - trvá odesílatel na tom, že příslušná smlouva je uzavřena teprve
>výslovným
>> dosažením shody na všech jejích náležitostech.
>> > - odesílatel tohoto emailu informuje, že není oprávněn uzavírat za
>> společnost žádné smlouvy s výjimkou případů, kdy k tomu byl písemně
>> zmocněn nebo písemně pověřen a takové pověření nebo plná moc byly
>> adresátovi tohoto emailu případně osobě, kterou adresát zastupuje,
>> předloženy nebo jejich existence je adresátovi či osobě jím
>zastoupené
>> známá.
>> >
>> > This e-mail and any documents attached to it may be confidential
>and are
>> intended only for its intended recipients.
>> > If you received this e-mail by mistake, please immediately inform
>its
>> sender. Delete the contents of this e-mail with all attachments and
>its copies
>> from your system.
>> > If you are not the intended recipient of this e-mail, you are not
>authorized
>> to use, disseminate, copy or disclose this e-mail in any manner.
>> > The sender of this e-mail shall not be liable for any possible
>damage caused
>> by modifications of the e-mail or by delay with transfer of the
>email.
>> >
>> > In case that this e-mail forms part of business dealings:
>> > - the sender reserves the right to end negotiations about entering
>into a
>> contract in any time, for any reason, and without stating any
>reasoning.
>> > - if the e-mail contains an offer, the recipient is entitled to
>immediately
>> accept such offer; The sender of this e-mail (offer) excludes any
>acceptance
>> of the offer on the part of the recipient containing any amendment or
>> variation.
>> > - the sender insists on that the respective contract is concluded
>only upon
>> an express mutual agreement on all its aspects.
>> > - the sender of this e-mail informs that he/she is not authorized
>to enter
>> into any contracts on behalf of the company except for cases in which
>he/she
>> is expressly authorized to do so in writing, and such authorization
>or power of
>> attorney is submitted to the recipient or the person represented by
>the
>> recipient, or the existence of such authorization is known to the
>recipient of
>> the person represented by the recipient.
>> >
>> >     [[alternative HTML version deleted]]
>> >
>> > ______________________________________________
>> > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide
>> > http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>>
>> --
>> Peter Dalgaard, Professor,
>> Center for Statistics, Copenhagen Business School Solbjerg Plads 3,
>2000
>> Frederiksberg, Denmark
>> Phone: (+45)38153501
>> Office: A 4.23
>> Email: pd....@cbs.dk  Priv: pda...@gmail.com
>
>
>________________________________
>Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a jsou
>určeny pouze jeho adresátům.
>Jestliže jste obdržel(a) tento e-mail omylem, informujte laskavě
>neprodleně jeho odesílatele. Obsah tohoto emailu i s přílohami a jeho
>kopie vymažte ze svého systému.
>Nejste-li zamýšleným adresátem tohoto emailu, nejste oprávněni tento
>email jakkoliv užívat, rozšiřovat, kopírovat či zveřejňovat.
>Odesílatel e-mailu neodpovídá za eventuální škodu způsobenou
>modifikacemi či zpožděním přenosu e-mailu.
>
>V případě, že je tento e-mail součástí obchodního jednání:
>- vyhrazuje si odesílatel právo ukončit kdykoliv jednání o uzavření
>smlouvy, a to z jakéhokoliv důvodu i bez uvedení důvodu.
>- a obsahuje-li nabídku, je adresát oprávněn nabídku bezodkladně
>přijmout; Odesílatel tohoto e-mailu (nabídky) vylučuje přijetí nabídky
>ze strany příjemce s dodatkem či odchylkou.
>- trvá odesílatel na tom, že příslušná smlouva je uzavřena teprve
>výslovným dosažením shody na všech jejích náležitostech.
>- odesílatel tohoto emailu informuje, že není oprávněn uzavírat za
>společnost žádné smlouvy s výjimkou případů, kdy k tomu byl písemně
>zmocněn nebo písemně pověřen a takové pověření nebo plná moc byly
>adresátovi tohoto emailu případně osobě, kterou adresát zastupuje,
>předloženy nebo jejich existence je adresátovi či osobě jím zastoupené
>známá.
>
>This e-mail and any documents attached to it may be confidential and
>are intended only for its intended recipients.
>If you received this e-mail by mistake, please immediately inform its
>sender. Delete the contents of this e-mail with all attachments and its
>copies from your system.
>If you are not the intended recipient of this e-mail, you are not
>authorized to use, disseminate, copy or disclose this e-mail in any
>manner.
>The sender of this e-mail shall not be liable for any possible damage
>caused by modifications of the e-mail or by delay with transfer of the
>email.
>
>In case that this e-mail forms part of business dealings:
>- the sender reserves the right to end negotiations about entering into
>a contract in any time, for any reason, and without stating any
>reasoning.
>- if the e-mail contains an offer, the recipient is entitled to
>immediately accept such offer; The sender of this e-mail (offer)
>excludes any acceptance of the offer on the part of the recipient
>containing any amendment or variation.
>- the sender insists on that the respective contract is concluded only
>upon an express mutual agreement on all its aspects.
>- the sender of this e-mail informs that he/she is not authorized to
>enter into any contracts on behalf of the company except for cases in
>which he/she is expressly authorized to do so in writing, and such
>authorization or power of attorney is submitted to the recipient or the
>person represented by the recipient, or the existence of such
>authorization is known to the recipient of the person represented by
>the recipient.
>______________________________________________
>R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

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