Otdfbt

Minor Revision with suggestion of an alternative proof by reviewer

Does a large simulator bay have standard public address announcements?

Why do games have consumables?

What is the most expensive material in the world that could be used to create Pun-Pun's lute?

How much cash can I safely carry into the USA and avoid civil forfeiture?

Function pointer with named arguments?

What happened to Captain America in Endgame?

How to fry ground beef so it is well-browned

Like totally amazing interchangeable sister outfits II: The Revenge

Who was the lone kid in the line of people at the lake at the end of Avengers: Endgame?

"You've called the wrong number" or "You called the wrong number"

Why does Mind Blank stop the Feeblemind spell?

Why did C use the -> operator instead of reusing the . operator?

a sore throat vs a strep throat vs strep throat

Why didn't the Space Shuttle bounce back into space as many times as possible so as to lose a lot of kinetic energy up there?

Converting a sprinkler system's 24V AC outputs to 3.3V DC logic inputs

How can I practically buy stocks?

Why does nature favour the Laplacian?

Rivers without rain

Implications of cigar-shaped bodies having rings?

Alignment of various blocks in tikz

What does the integral of a function times a function of a random variable represent, conceptually?

Does tea made with boiling water cool faster than tea made with boiled (but still hot) water?

Is Diceware more secure than a long passphrase?

Virtual layer functionality does not seem to support memory layers

Spatial join for closest features and using a sum merge rule in QGISMemory Vector Layer Corrupted?Is it possible to use memory layers in QGIS processing algorithms?QGIS python originalName() does not return actual original layer nameVirtual fields are lost when duplicate layersQGIS virtual layer path never saved as relativeClipping virtual raster generates out of memory errorLoad non-spatial table in QGIS by querying an Oracle databaseAdd layer to existing geopackage not working in QGIS?Virtual layer from query with special characters in field name using PyQGISSpatial Query for a Virtual Layer

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

3

I have a memory layer loaded in the QGIS virtual layer in the data source manager. I am trying to run a very simple query:

select * from layer

Here is a snapshot:

While this works for the physical layer, it does not work for the memory layer. They output virtual layer is blank, and I know that my memory layer has attribute data.

Is this simply a bug? I want to keep this a memory layer to reduce the number of steps I need to do to arrive at my final result. Should I resort to another tool or is there a workaround?

EDIT

Also found this quote in this link:

Creating a virtual layer with the layer_ref key allows to directly access already loaded QGIS layers (including memory layers).

qgis virtual-layer

share|improve this question

edited Apr 20 at 12:52

underdark♦

69.4k13179351

asked Apr 19 at 9:12

user32882user32882

1,17611127

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Just tested right now : i had no problem of this kind (Q3.44) ... Are you sure of your data structure ?
  
  – snaileater
  Apr 19 at 9:28
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  what do you mean by data structure? I am just calling all columns in the table I loaded.... Using QGIS3.2.2 by the way
  
  – user32882
  Apr 19 at 9:29
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  When u open its attribute table in the layer manager you see all the features (those u would like to get when querying it) ? Do u just get an empty answer or any error message ? Did u try a select count(*) from memory_layer ?
  
  – snaileater
  Apr 19 at 9:33
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The resulting virtual layer is empty (no attributes, no fields). The original memory layer has plenty of attributes... I'm updating QGIS now to see if it has been fixed
  
  – user32882
  Apr 19 at 9:36
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Nope... doesn't work with QGIS 3.4.6... Are you sure you tested a memory layer?
  
  – user32882
  Apr 19 at 9:43
  

  
  
  
  

 | 
show 2 more comments

3

I have a memory layer loaded in the QGIS virtual layer in the data source manager. I am trying to run a very simple query:

select * from layer

Here is a snapshot:

While this works for the physical layer, it does not work for the memory layer. They output virtual layer is blank, and I know that my memory layer has attribute data.

Is this simply a bug? I want to keep this a memory layer to reduce the number of steps I need to do to arrive at my final result. Should I resort to another tool or is there a workaround?

EDIT

Also found this quote in this link:

Creating a virtual layer with the layer_ref key allows to directly access already loaded QGIS layers (including memory layers).

qgis virtual-layer

share|improve this question

edited Apr 20 at 12:52

underdark♦

69.4k13179351

asked Apr 19 at 9:12

user32882user32882

1,17611127

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Just tested right now : i had no problem of this kind (Q3.44) ... Are you sure of your data structure ?
  
  – snaileater
  Apr 19 at 9:28
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  what do you mean by data structure? I am just calling all columns in the table I loaded.... Using QGIS3.2.2 by the way
  
  – user32882
  Apr 19 at 9:29
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  When u open its attribute table in the layer manager you see all the features (those u would like to get when querying it) ? Do u just get an empty answer or any error message ? Did u try a select count(*) from memory_layer ?
  
  – snaileater
  Apr 19 at 9:33
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The resulting virtual layer is empty (no attributes, no fields). The original memory layer has plenty of attributes... I'm updating QGIS now to see if it has been fixed
  
  – user32882
  Apr 19 at 9:36
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Nope... doesn't work with QGIS 3.4.6... Are you sure you tested a memory layer?
  
  – user32882
  Apr 19 at 9:43
  

  
  
  
  

 | 
show 2 more comments

I have a memory layer loaded in the QGIS virtual layer in the data source manager. I am trying to run a very simple query:

select * from layer

Here is a snapshot:

While this works for the physical layer, it does not work for the memory layer. They output virtual layer is blank, and I know that my memory layer has attribute data.

Is this simply a bug? I want to keep this a memory layer to reduce the number of steps I need to do to arrive at my final result. Should I resort to another tool or is there a workaround?

EDIT

Also found this quote in this link:

Creating a virtual layer with the layer_ref key allows to directly access already loaded QGIS layers (including memory layers).

qgis virtual-layer

share|improve this question

edited Apr 20 at 12:52

underdark♦

69.4k13179351

asked Apr 19 at 9:12

user32882user32882

1,17611127

select * from layer

share|improve this question

edited Apr 20 at 12:52

underdark♦

69.4k13179351

asked Apr 19 at 9:12

user32882user32882

1,17611127

share|improve this question

edited Apr 20 at 12:52

underdark♦

69.4k13179351

asked Apr 19 at 9:12

user32882user32882

1,17611127

edited Apr 20 at 12:52

underdark♦

69.4k13179351

edited Apr 20 at 12:52

underdark♦

69.4k13179351

asked Apr 19 at 9:12

user32882user32882

1,17611127

asked Apr 19 at 9:12

user32882user32882

1,17611127

2 Answers
2

active

oldest

votes

2

You can find all your layers in the DB-manager. There (in my opinion) it is easier to access and query them. And you can load results as a new layer.

• Go to DB-manager > Virtual Layers > QGIS layers




• Select one of the layers and make your query. Note that the geometry is written as geometry and not geom.

share|improve this answer

edited Apr 19 at 11:33

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The DB Manager is much better and could be a good segway into PostGIS, spatialite or other db-type gis systems. Do you know if the geometry column can be manipulated in here to do spatial queries as well? Perhaps I don't need that NNJoin plugin after all.... that would be nice
  
  – user32882
  Apr 19 at 13:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I never used the NNjoin before. So I do not know which functionality it has. But probably it would perform the same with spatialite or postgis
  
  – PieterB
  Apr 23 at 7:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To answer your question @user32882 you can easily perform spatial joins and nearest neighbour queries in DB Manager using SQL. It may not be that fast if you are using shapefiles in DB manager, but it is dynamic and much more flexible (pick which columns to join, distance threshold for nearest neighbour, etc). If you use spatialite you can access the VirtualKNN feature directly within DB Manager. SQL is well worth exploring
  
  – she_weeds
  14 hours ago
  

  
  
  
  

add a comment | 

3

The upper section, embeded layers, allows listing (and using) layers that are not loaded in QGIS table of content.

Using an in-memory layer that is not loaded in QGIS is to be tested. I believe the layer is cleared from memory as soon as it is removed from the table of content.

If you do have the in-memory layer loaded in the table of content, you can simply remove it from the embeded layers section, and the query will work. I just reproduced your use case and workaround in 3.4.5

share|improve this answer

answered Apr 19 at 11:23

JGHJGH

13.9k21339

add a comment | 

Your Answer

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "79"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fgis.stackexchange.com%2fquestions%2f319324%2fvirtual-layer-functionality-does-not-seem-to-support-memory-layers%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

2

You can find all your layers in the DB-manager. There (in my opinion) it is easier to access and query them. And you can load results as a new layer.

• Go to DB-manager > Virtual Layers > QGIS layers




• Select one of the layers and make your query. Note that the geometry is written as geometry and not geom.

share|improve this answer

edited Apr 19 at 11:33

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The DB Manager is much better and could be a good segway into PostGIS, spatialite or other db-type gis systems. Do you know if the geometry column can be manipulated in here to do spatial queries as well? Perhaps I don't need that NNJoin plugin after all.... that would be nice
  
  – user32882
  Apr 19 at 13:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I never used the NNjoin before. So I do not know which functionality it has. But probably it would perform the same with spatialite or postgis
  
  – PieterB
  Apr 23 at 7:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To answer your question @user32882 you can easily perform spatial joins and nearest neighbour queries in DB Manager using SQL. It may not be that fast if you are using shapefiles in DB manager, but it is dynamic and much more flexible (pick which columns to join, distance threshold for nearest neighbour, etc). If you use spatialite you can access the VirtualKNN feature directly within DB Manager. SQL is well worth exploring
  
  – she_weeds
  14 hours ago
  

  
  
  
  

add a comment | 

2

You can find all your layers in the DB-manager. There (in my opinion) it is easier to access and query them. And you can load results as a new layer.

• Go to DB-manager > Virtual Layers > QGIS layers




• Select one of the layers and make your query. Note that the geometry is written as geometry and not geom.

share|improve this answer

edited Apr 19 at 11:33

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The DB Manager is much better and could be a good segway into PostGIS, spatialite or other db-type gis systems. Do you know if the geometry column can be manipulated in here to do spatial queries as well? Perhaps I don't need that NNJoin plugin after all.... that would be nice
  
  – user32882
  Apr 19 at 13:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I never used the NNjoin before. So I do not know which functionality it has. But probably it would perform the same with spatialite or postgis
  
  – PieterB
  Apr 23 at 7:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To answer your question @user32882 you can easily perform spatial joins and nearest neighbour queries in DB Manager using SQL. It may not be that fast if you are using shapefiles in DB manager, but it is dynamic and much more flexible (pick which columns to join, distance threshold for nearest neighbour, etc). If you use spatialite you can access the VirtualKNN feature directly within DB Manager. SQL is well worth exploring
  
  – she_weeds
  14 hours ago
  

  
  
  
  

add a comment | 

You can find all your layers in the DB-manager. There (in my opinion) it is easier to access and query them. And you can load results as a new layer.

• Go to DB-manager > Virtual Layers > QGIS layers




• Select one of the layers and make your query. Note that the geometry is written as geometry and not geom.

share|improve this answer

edited Apr 19 at 11:33

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

share|improve this answer

edited Apr 19 at 11:33

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

answered Apr 19 at 11:01

PieterBPieterB

3,2001129

3

The upper section, embeded layers, allows listing (and using) layers that are not loaded in QGIS table of content.

Using an in-memory layer that is not loaded in QGIS is to be tested. I believe the layer is cleared from memory as soon as it is removed from the table of content.

If you do have the in-memory layer loaded in the table of content, you can simply remove it from the embeded layers section, and the query will work. I just reproduced your use case and workaround in 3.4.5

share|improve this answer

answered Apr 19 at 11:23

JGHJGH

13.9k21339

add a comment | 

3

The upper section, embeded layers, allows listing (and using) layers that are not loaded in QGIS table of content.

Using an in-memory layer that is not loaded in QGIS is to be tested. I believe the layer is cleared from memory as soon as it is removed from the table of content.

If you do have the in-memory layer loaded in the table of content, you can simply remove it from the embeded layers section, and the query will work. I just reproduced your use case and workaround in 3.4.5

share|improve this answer

answered Apr 19 at 11:23

JGHJGH

13.9k21339

add a comment | 

The upper section, embeded layers, allows listing (and using) layers that are not loaded in QGIS table of content.

Using an in-memory layer that is not loaded in QGIS is to be tested. I believe the layer is cleared from memory as soon as it is removed from the table of content.

If you do have the in-memory layer loaded in the table of content, you can simply remove it from the embeded layers section, and the query will work. I just reproduced your use case and workaround in 3.4.5

share|improve this answer

answered Apr 19 at 11:23

JGHJGH

13.9k21339

share|improve this answer

answered Apr 19 at 11:23

JGHJGH

13.9k21339

answered Apr 19 at 11:23

JGHJGH

13.9k21339

answered Apr 19 at 11:23

JGHJGH

13.9k21339