After creating tab bars and widgets the emulator gives such an error when opening the app [closed] - flutter

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I could not transfer my code to the site as I wrote it, but I placed your photo Please can you help me?


You are getting the error because you are trying to pass an uninitialized String to a Text-Widget (Naber). A Text-Widget can not handle uninitialized Strings which have the value null.
Therefore try initializing the String 'Naber' directly like:
String Naber = 'Some text';
This should work.

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ERROR: invalid input syntax for type double precision: "$13.99" [closed]

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ERROR: invalid input syntax for type double precision: "$13.99".CONTEXT: COPY customer_purchase, line 2, column product_price: "$13.99".
This error pops up when I try to copy table from csv to sql database.I know the problem here is due to wrong data type used. And, I tried using every possible data type but still could not solve the problem.
I was trying to copy CSV table from excel to sql database(postgresql) and instead of showing output, an error occured.

Why does 'mkt_carrier_fl_num AS flight' return a syntax error 42601? [closed]

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I'm new to Postgres and everything databases. I'm learning through a Pluralsight course and have finally managed to import a database. Following along with what the teacher is typing out, I query:
SELECT fl_date,
mkt_carrier AS airline
mkt_carrier_fl_num AS flight
origin,
dest
FROM performance
WHERE origin = 'ORD'
.. from a database that came with the course files, and get back this:
ERROR: syntax error at or near "mkt_carrier_fl_num"
LINE 3: mkt_carrier_fl_num AS flight
^
SQL state: 42601
Character: 45
I've googled the error code but apparently this can entail many different things. I have no idea where to go from here. Literally every function in this program is a mystery to me.
Please help.

SELECT fl_date
,mkt_carrier AS airline -- comma before the start of the column name
,mkt_carrier_fl_num AS flight
,origin
,dest
FROM performance
WHERE origin = 'ORD';

where clause not working in firestore flutter [closed]

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I am trying to use where clause in flutter but it is returning null though data is there in firestore. Here is my code:
Future<List<DocumentSnapshot>> fetchInitialBatch() async {
return (await Firestore.instance
.collection("videos")
.where("category", isEqualTo: category)
.orderBy("url")
.limit(3)
.getDocuments())
.documents;
}
Here is screenshot of firestore:image link
What is missing in it?

First make sure the that fields do not have any space or unnecessary character messing up the query. Secondly, try to invert the order of the statement and see if it work do it like below.
You can even delete each field and create them again to see if will works. Either than that I do not see that you done something wrong, for me is more like is reading something blank from the firebase itself on the fields.
Future<List<DocumentSnapshot>> fetchInitialBatch() async {
return (awaitFirestore.instance.collection("videos")
.orderBy('url').limit(3).where("category",isEqualTo: category).
getDocuments()).documents;
}

web2py form with DB check [closed]

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I'm using web2py forms, but I need to set up a limit for 20 users registration. How can I do it?
PS: Edit to make easy to understand
Thanks in advance.
Best regards!

Assuming you wish to limit registration to a maximum of 20 users and you are using the standard /default/user function from the scaffolding application:
In the default.py controller:
def user():
if request.args(0) == 'register' and db.auth_user.count() >= 20:
form = None
else:
form = auth()
return dict(form=form)
In the default/user.html view:
{{if form is None:}}
<p>Sorry, no more registrations allowed.</p>
{{else:}}
{{=form}}
{{pass}}

Please anyone be so kind help! Matlab [closed]

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I have this data of year, month, date. I want this to show as year,month,date in Matlab and don't know how to do.
X=(2014,01,02 2014,01,03 2014,01,07 2014,01,08 2014,01,09 2014,01,10 2014,01,13
2014,01,14 2014,01,15 2014,01,16 2014,01,17 2014,01,20 2014,01,21 2014,01,22
2014,01,23 2014,01,24 2014,01,27 2014,01,28 2014,01,29 2014,01,30 2014,01,31
2014,02,03 2014,02,04 2014,02,05 2014,02,06 2014,02,07 2014,02,10 2014,02,11
2014,02,12 2014,02,13 2014,02,14 2014,02,17 2014,02,18 2014,02,19 2014,02,20
2014,02,21 2014,02,24 2014,02,25 2014,02,26 2014,02,27 2014,02,28 2014,03,03)

The simplest way would be to reshape the matrix and use it accordingly. I demonstrate the way to reshape and print all the dates in US (MM/DD/YYYY) format.
X=[2014,01,02 2014,01,03 2014,01,07 2014,01,08 2014,01,09 2014,01,10 2014,01,13 2014,01,14 2014,01,15 2014,01,16 2014,01,17 2014,01,20 2014,01,21 2014,01,22 2014,01,23 2014,01,24 2014,01,27 2014,01,28 2014,01,29 2014,01,30 2014,01,31 2014,02,03 2014,02,04 2014,02,05 2014,02,06 2014,02,07 2014,02,10 2014,02,11 2014,02,12 2014,02,13 2014,02,14 2014,02,17 2014,02,18 2014,02,19 2014,02,20 2014,02,21 2014,02,24 2014,02,25 2014,02,26 2014,02,27 2014,02,28 2014,03,03];
X_in_better_format = reshape(X,3,42)';
for it = 1:size(X_in_better_format,1)
sprintf('The date is %d/%d/%d',X_in_better_format(it,2),X_in_better_format(it,3),X_in_better_format(it,1)) %US Format
end