Found:

    CREATE TABLE publishers(id INT, info JSON); 
    CREATE INDEX ON publishers((info-&gt;&gt;&#39;name&#39;));

As stated in the comments, the subtle difference here is `-&gt;&gt;` instead of `-&gt;`. The former one returns the value as text, the latter as a JSON object.

I am using Angular JS and I need to set a selected option of a dropdown list control using angular JS. Forgive me if this is ridiculous but I am new with Angular JS 

Here is the dropdown list control of my html

 

     &lt;select ng-required=&quot;item.id==8 &amp;&amp; item.quantity &gt; 0&quot; name=&quot;posterVariants&quot;
       ng-show=&quot;item.id==8&quot; ng-model=&quot;item.selectedVariant&quot; 
       ng-change=&quot;calculateServicesSubTotal(item)&quot;
       ng-options=&quot;v.name for v in variants | filter:{type:2}&quot;&gt;
      &lt;/select&gt;

After it gets populated I get 

   

     &lt;select ng-options=&quot;v.name for v in variants | filter:{type:2}&quot; ng-change=&quot;calculateServicesSubTotal(item)&quot;
    ng-model=&quot;item.selectedVariant&quot; ng-show=&quot;item.id==8&quot; name=&quot;posterVariants&quot;
    ng-required=&quot;item.id==8 &amp;amp;&amp;amp; item.quantity &amp;gt; 0&quot; class=&quot;ng-pristine ng-valid ng-valid-required&quot;&gt;
    	&lt;option value=&quot;?&quot; selected=&quot;selected&quot;&gt;&lt;/option&gt;
    	&lt;option value=&quot;0&quot;&gt;set of 6 traits&lt;/option&gt;
    	&lt;option value=&quot;1&quot;&gt;5 complete sets&lt;/option&gt;
    &lt;/select&gt;

How can I set the control for `value=&quot;0&quot;` to be selected?

How to set a selected option of a dropdown list control using angular JS

You can remove an item from a database using EF by using the following two methods.

 - [EntityCollection&lt;TEntity&gt;.Remove Method][1]

 - [ObjectContext.DeleteObject Method][2]


The first is on the `EntityCollection` and the second on the `ObjectContext`.

When should each be used? 

Is one prefered over the other?

`Remove()` returns a `bool` and `DeleteObject()` returns `void`.

  [1]: http://msdn.microsoft.com/en-us/library/bb337024.aspx
  [2]: http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.deleteobject.aspx

Entity Framework .Remove() vs. .DeleteObject()

In PostgreSQL 9.3 Beta 2 (?), how do I create an index on a JSON field? I tried it using the `-&gt;` operator used for `hstore` but got the following error:

     CREATE TABLE publishers(id INT, info JSON);
     CREATE INDEX ON publishers((info-&gt;&#39;name&#39;));

&gt; ERROR:  data type json has no default operator class for access method
&gt; &quot;btree&quot; HINT:  You must specify an operator class for the index or
&gt; define a default operator class for the data type.



How to create index on JSON field in Postgres?

In PostgreSQL 9.3 Beta 2 (?), how do I create an index on a JSON field? I tried it using the <code>-></code> operator used for <code>hstore</code> but got the following error:
<pre><code class="hljs language-sql"> CREATE TABLE publishers(id INT, info JSON);
 CREATE INDEX ON publishers((info->'name'));
</code></pre>
> ERROR: data type json has no default operator class for access method
> "btree" HINT: You must specify an operator class for the index or
> define a default operator class for the data type.

How can I create a JSON with this format in Android:
Since the API that I will be passing will parse JsonArray then the object.
Or would it be okay if just to pass a json object? Since I will just have to insert 1 transaction per service  call.

	{
		&quot;student&quot;: [
			{
				&quot;id&quot;: 1,
				&quot;name&quot;: &quot;John Doe&quot;,
				&quot;year&quot;: &quot;1st&quot;,
				&quot;curriculum&quot;: &quot;Arts&quot;,
				&quot;birthday&quot;: 3/3/1995
			},
			{
				&quot;id&quot;: 2,
				&quot;name&quot;: &quot;Michael West&quot;,
				&quot;year&quot;: &quot;2nd&quot;,
				&quot;curriculum&quot;: &quot;Economic&quot;,
				&quot;birthday&quot;: 4/4/1994
			}
		]
	}

What I know is only the JSONObject.
Like this one.

    JSONObject obj = new JSONObject();
    try {
		obj.put(&quot;id&quot;, &quot;3&quot;);
		obj.put(&quot;name&quot;, &quot;NAME OF STUDENT&quot;);
		obj.put(&quot;year&quot;, &quot;3rd&quot;);
		obj.put(&quot;curriculum&quot;, &quot;Arts&quot;);
		obj.put(&quot;birthday&quot;, &quot;5/5/1993&quot;);
	} catch (JSONException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}

Any ideas. Thanks

Android- create JSON Array and JSON Object

Here  is my model with a JSON response:

    exports.getUser = function(req, res, callback) {
     	User.find(req.body, function (err, data) {
			if (err) {
				res.json(err.errors);
			} else {
				res.json(data);
			}
	   });
    };

Here I get it via `http.request`. Why do I receive (data) a string and not a JSON?

     var options = {
	  hostname: &#39;127.0.0.1&#39;
	  ,port: app.get(&#39;port&#39;)
	  ,path: &#39;/users&#39;
	  ,method: &#39;GET&#39;
	  ,headers: { &#39;Content-Type&#39;: &#39;application/json&#39; }
	};

	var req = http.request(options, function(res) {
	  res.setEncoding(&#39;utf8&#39;);
	  res.on(&#39;data&#39;, function (data) {
	       console.log(data); // I can&#39;t parse it because, it&#39;s a string. why?
	  });
	});
	reqA.on(&#39;error&#39;, function(e) {
	  console.log(&#39;problem with request: &#39; + e.message);
	});
	reqA.end();

How can I get a JSON?

Get a JSON via HTTP request in NodeJS

I have a project where I am using Spring MVC + Jackson to build a REST service. Let&#39;s say I have the following java entity

    public class MyEntity {
    	private Integer id;
    	private boolean aBoolean;
    	private String aVeryBigString;
    	//getter &amp; setters
    }

Sometimes, I just want to update the boolean value, and I don&#39;t think that sending the whole object with its big string is a good idea just to update a simple boolean. So, I have considered using the PATCH HTTP method to only send the fields that need to be updated. So, I declare the following method in my controller:

    @RequestMapping(method = RequestMethod.PATCH)
    public void patch(@RequestBody MyVariable myVariable) {
    	//calling a service to update the entity
    }

The problem is: how do I know which fields need to be updated? For instance, if the client just wants to update the boolean, I will get an object with an empty &quot;aVeryBigString&quot;. How am I supposed to know that the user just wants to update the boolean, but does not want to empty the string? 

I have &quot;solved&quot; the problem by building custom URLs. For instance, the following URL: POST /myentities/1/aboolean/true will be mapped to a method that allows to only update the boolean. The problem with this solution is that it is not REST compliant. I don&#39;t want to be 100% REST compliant, but I do not feel comfortable with providing a custom URL to update each field (especially given that it causes problems when I want to update several fields).

Another solution would be to split &quot;MyEntity&quot; into multiple resources and just update these resources, but I feel like it does not make sense: &quot;MyEntity&quot; **is** a plain resource, it is not **composed of** other resources.

So, is there an elegant way of solving this problem?

Spring MVC PATCH method: partial updates

My bean looks like this:

    class MyBean {
    	
    	private @JsonUnwrapped HashMap&lt;String, String&gt; map = new HashMap&lt;String, String&gt;();
    	
    	private String name;
    	
    	public HashMap&lt;String, String&gt; getMap() {
    		return map;
    	}
    
    	public void setMap(HashMap&lt;String, String&gt; map) {
    		this.map = map;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    }

While I&#39;m serializing the bean using the following code: 

    MyBean bean = new MyBean();
    HashMap&lt;String, String&gt; map = new HashMap&lt;String, String&gt;();;
    map.put(&quot;key1&quot;, &quot;value1&quot;);
    map.put(&quot;key2&quot;, &quot;value2&quot;);
    bean.setMap(map);
    bean.setName(&quot;suren&quot;);
    ObjectMapper mapper = new ObjectMapper();
    System.out.println(&quot;\n&quot;+mapper.writeValueAsString(bean));

I&#39;m getting result like this:

    {&quot;map&quot;:{&quot;key2&quot;:&quot;value2&quot;,&quot;key1&quot;:&quot;value1&quot;},&quot;name&quot;:&quot;suren&quot;}

but

    {&quot;key2&quot;:&quot;value2&quot;,&quot;key1&quot;:&quot;value1&quot;,&quot;name&quot;:&quot;suren&quot;}

is expected per the [JacksonFeatureUnwrapping documentation](http://wiki.fasterxml.com/JacksonFeatureUnwrapping). Why am I not getting the unwrapped result?

Why I&#39;m not able to unwrap and serialize a Java map using the Jackson Java library?

I want to get a `JSON` object from a Http get response:

Here is my current code for the Http get:

    protected String doInBackground(String... params) {

		HttpClient client = new DefaultHttpClient();
		HttpGet request = new HttpGet(params[0]);
		HttpResponse response;
		String result = null;
		try {
			response = client.execute(request);			
			HttpEntity entity = response.getEntity();
			
			if (entity != null) {

				// A Simple JSON Response Read
				InputStream instream = entity.getContent();
				result = convertStreamToString(instream);
				// now you have the string representation of the HTML request
				System.out.println(&quot;RESPONSE: &quot; + result);
				instream.close();
				if (response.getStatusLine().getStatusCode() == 200) {
					netState.setLogginDone(true);
				}

			}
			// Headers
			org.apache.http.Header[] headers = response.getAllHeaders();
			for (int i = 0; i &lt; headers.length; i++) {
				System.out.println(headers[i]);
			}
		} catch (ClientProtocolException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (IOException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
		return result;
	}

Here is the convertSteamToString function:

    private static String convertStreamToString(InputStream is) {
		
		BufferedReader reader = new BufferedReader(new InputStreamReader(is));
		StringBuilder sb = new StringBuilder();

		String line = null;
		try {
			while ((line = reader.readLine()) != null) {
				sb.append(line + &quot;\n&quot;);
			}
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				is.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		return sb.toString();
	}


Right now I am just getting a string object. How can I get a JSON object back.

Get a JSON object from a HTTP response

After restarting my MacBook Pro I am unable to start the database server: 

    could not connect to server: No such file or directory
	Is the server running locally and accepting
	connections on Unix domain socket &quot;/tmp/.s.PGSQL.5432&quot;?

I checked the logs and the following line appears over and over again:

    FATAL:  database files are incompatible with server
    DETAIL:  The data directory was initialized by PostgreSQL version 9.2, which is not compatible with this version 9.0.4.

9.0.4 was the version that came preinstalled on the mac, 9.2[.4] is the version I installed via Homebrew. 
As mentioned, this used to work before the restart, so it can&#39;t actually be an compiling issue. I also re-ran `initdb /usr/local/var/postgres -E utf8` and the file still exists.

Unfortunately, I am pretty new to Postgres, so any help would be very much appreciated.

Postgres - FATAL: database files are incompatible with server

I am looking for a way to implement the [SQLServer-function datediff][1] in PostgreSQL. That is, this function returns the count (as a signed integer value) of the specified datepart boundaries crossed between the specified start date and end date.

    datediff(dd, &#39;2010-04-01&#39;, &#39;2012-03-05&#39;) = 704 // 704 changes of day in this interval
    datediff(mm, &#39;2010-04-01&#39;, &#39;2012-03-05&#39;) = 23  // 23 changes of month
    datediff(yy, &#39;2010-04-01&#39;, &#39;2012-03-05&#39;) = 2   // 2 changes of year

I know I could do &#39;dd&#39; by simply using subtraction, but any idea about the other two?


  [1]: https://docs.microsoft.com/en-us/sql/t-sql/functions/datediff-transact-sql?view=sql-server-2017

How to get difference of days/months/years (datediff) between two dates?

I have an application in which I&#39;ve used MySQL. I had a report that stretched records of the last 24 hours. I used the query:


    WHERE (DATE_SUB(CURDATE(), INTERVAL 1 DAY) &lt;= FROM_UNIXTIME(`workorder`.`CREATEDTIME` / 1000))


Now I have to use PostgreSQL and do not know how to make a report of the last 24 hours.
Can any of you help?


records from yesterday in postrgesql

A password is visible in my psql prompt (by pushing up arrow to view previous inputted commands). So I would like to delete that entry from the psql client. 

Other resources([1], [2]) claim that psql client history is kept in is a `~/.psql_history` file, however this file is simply not there. (it&#39;s not in `.bash_history` either)

So **there must be another file where the history of psql prompt is kept, any ideas where?**

I log in to my prompt like this 
`sudo -u postgres psql my_db`

Note: I am working on `Ubuntu 12.04`


  [1]: http://www.thegeekstuff.com/2009/04/15-practical-postgresql-database-adminstration-commands/
  [2]: https://stackoverflow.com/questions/6654121/postgresql-psql-history-to-dev-null

Where is psql client history kept? (~/.psql_history non-existent!)

Having a bit of an issue with PostgreSQL on Mac OS X 10.8.4. I accidentally did `brew rm postgresql --force` while the postgres server was running. When I installed using `brew install postgresql` and ran `pg_ctl -D /usr/local/var/postgres start` I get:

    pg_ctl: another server might be running; trying to start server anyway
    server starting
    FATAL:  lock file &quot;postmaster.pid&quot; already exists                                                                       
    HINT:  Is another postmaster (PID 752) running in data directory &quot;/usr/local/var/postgres&quot;?

when I run &quot;ps -ef | grep postgres&quot; I get:

    501   752   235   0 12:42PM ??         0:00.01 /usr/local/opt/postgresql/bin/postgres -D /usr/local/var/postgres -r /usr/local/var/postgres/server.log
    501   754   752   0 12:42PM ??         0:00.00 postgres: checkpointer process       
    501   755   752   0 12:42PM ??         0:00.34 postgres: writer process       
    501   756   752   0 12:42PM ??         0:00.02 postgres: wal writer process       
    501   757   752   0 12:42PM ??         0:00.01 postgres: autovacuum launcher process       
    501   758   752   0 12:42PM ??         0:00.01 postgres: stats collector process       
    501   945   452   0 12:58PM ttys000    0:00.00 grep postgres

when I try to stop the server with `pg_ctl stop -D /usr/local/var/postgres -m fast` or `pg_ctl -D /usr/local/var/postgres stop -mi` I get: 


    waiting for server to shut down........................................... Failed
    pg_ctl: server does not shut down

**EDIT**

    which pg_ctl
    /usr/local/bin/pg_ctl
    pg_ctl --version
    pg_ctl (PostgreSQL) 9.2.4

Gist of `server.log`: https://gist.github.com/anonymous/6106182


PostgreSQL server won&#39;t stop

I&#39;ve programmatically created a new document collection using the MongoDB C# driver.

At this point I want to create and build indexes programmatically. How can I do that?

How to create indexes in MongoDB via .NET

Code example:

    In [171]: A = np.array([1.1, 1.1, 3.3, 3.3, 5.5, 6.6])
    
    In [172]: B = np.array([111, 222, 222, 333, 333, 777])
    
    In [173]: C = randint(10, 99, 6)
    
    In [174]: df = pd.DataFrame(zip(A, B, C), columns=[&#39;A&#39;, &#39;B&#39;, &#39;C&#39;])
    
    In [175]: df.set_index([&#39;A&#39;, &#39;B&#39;], inplace=True)
    
    In [176]: df
    Out[176]: 
              C
    A   B      
    1.1 111  20
        222  31
    3.3 222  24
        333  65
    5.5 333  22
    6.6 777  74 

Now, I want to retrieve A values:  
**Q1**: in range [3.3, 6.6] - expected return value: [3.3, 5.5, 6.6] or [3.3, 3.3, 5.5, 6.6] in case last inclusive, and [3.3, 5.5] or [3.3, 3.3, 5.5] if not.  
**Q2**: in range [2.0, 4.0] - expected return value: [3.3] or [3.3, 3.3]  

Same for any other *MultiIndex* dimension, for example B values:  
**Q3**: in range [111, 500] with repetitions, as number of data rows in range - expected return value: [111, 222, 222, 333, 333]    

More formal:

Let us assume T is a table with columns A, B and C. The table includes *n* rows. Table cells are numbers, for example A double, B and C integers. Let&#39;s create a *DataFrame* of table T, let us name it DF. Let&#39;s set columns A and B indexes of DF (without duplication, i.e. no separate columns A and B as indexes, and separate as data), i.e. A and B in this case *MultiIndex*.  
  
Questions:  

 1. How to write a query on the index, for example, to query the index A (or B), say in the labels interval [120.0, 540.0]? Labels 120.0 and 540.0 exist. I must clarify that I am interested only in the list of indices as a response to the query!
 2. How to the same, but in case of the labels 120.0 and 540.0 do not exist, but there are labels by value lower than 120, higher than 120 and less than 540, or higher than 540?
 3. In case the answer for Q1 and Q2 was unique index values, now the same, but with repetitions, as number of data rows in index range.

I know the answers to the above questions in the case of columns which are not indexes, but in the indexes case, after a long research in the web and experimentation with the functionality of *pandas*, I did not succeed. The only method (without additional programming) I see now is to have a duplicate of A and B as data columns in addition to index.


How to query MultiIndex index columns values in pandas

I want to add an index to a table column in my MySQL database. I am using Doctrine 2 to create my database schemas.

I know that I can use

```lang-php
/** @Id @Column(type=&quot;integer&quot;) */
```

to create primary keys. But my column shall neither have the `unique` nor the `primary key` attribute. It shall simply be an `index` in my table (MySQL knows these three types).

What is the proper statement to create such an index?

How can I add an INDEX with Doctrine 2 to a column without making it a primary key?

In Python we can get the index of a value in an array by using `.index()`. 

But with a NumPy array, when I try to do:

    decoding.index(i)

I get:

&gt;AttributeError: &#39;numpy.ndarray&#39; object has no attribute &#39;index&#39;

How could I do this on a NumPy array?


Index of element in NumPy array

I&#39;ve got a data frame **df1** with multiple columns and rows. Simple example:

        TIME T1  T2 
           1 10 100
           2 20 200
           3 30 300

I&#39;d like to create an empty data frame **df2** and later on, add new columns with the calculation results.

For this moment my code looks like this:
&lt;!-- language: lang-py --&gt;

         df1=pd.read_csv(&quot;1.txt&quot;,index_col=&quot;TIME&quot;)

         df2=df1.copy()[[]] #copy df1 and erase all columns

...adding two new columns:
&lt;!-- language: lang-py --&gt;
        
         df2[&quot;results1&quot;],df2[&quot;results2&quot;]=df1[&quot;T1&quot;]*df[&quot;T2&quot;]*3,df1[&quot;T2&quot;]+100

Is there any better/safer/faster way to do this ? 
Is it possible to create an empty data frame df2 and only copy index from df1 ?
         

Create an empty data frame with index from another data frame

With postgresql 9.3 I can `SELECT` specific fields of a JSON data type, but how do you modify them using `UPDATE`? I can&#39;t find any examples of this in the postgresql documentation, or anywhere online. I have tried the obvious:

```sql
postgres=# create table test (data json);
CREATE TABLE
postgres=# insert into test (data) values (&#39;{&quot;a&quot;:1,&quot;b&quot;:2}&#39;);
INSERT 0 1
postgres=# select data-&gt;&#39;a&#39; from test where data-&gt;&gt;&#39;b&#39; = &#39;2&#39;;
 ?column?
----------
 1
(1 row)
postgres=# update test set data-&gt;&#39;a&#39; = to_json(5) where data-&gt;&gt;&#39;b&#39; = &#39;2&#39;;
ERROR:  syntax error at or near &quot;-&gt;&quot;
LINE 1: update test set data-&gt;&#39;a&#39; = to_json(5) where data-&gt;&gt;&#39;b&#39; = &#39;2...
```


How do I modify fields inside the new PostgreSQL JSON datatype?

I have a table to store information about my rabbits. It looks like this:

    create table rabbits (rabbit_id bigserial primary key, info json not null);
    insert into rabbits (info) values
      (&#39;{&quot;name&quot;:&quot;Henry&quot;, &quot;food&quot;:[&quot;lettuce&quot;,&quot;carrots&quot;]}&#39;),
      (&#39;{&quot;name&quot;:&quot;Herald&quot;,&quot;food&quot;:[&quot;carrots&quot;,&quot;zucchini&quot;]}&#39;),
      (&#39;{&quot;name&quot;:&quot;Helen&quot;, &quot;food&quot;:[&quot;lettuce&quot;,&quot;cheese&quot;]}&#39;);

How should I find the rabbits who like carrots? I came up with this:

    select info-&gt;&gt;&#39;name&#39; from rabbits where exists (
      select 1 from json_array_elements(info-&gt;&#39;food&#39;) as food
      where food::text = &#39;&quot;carrots&quot;&#39;
    );

I don&#39;t like that query. It&#39;s a mess.

As a full-time rabbit-keeper, I don&#39;t have time to change my database schema. I just want to properly feed my rabbits. Is there a more readable way to do that query?

Check if a Postgres JSON array contains a string

I have a sequence on postgresql 9.3 inside a schema.

I can do this:

```
SELECT last_value, increment_by from foo.&quot;SQ_ID&quot;;`
```

    last_value | increment_by
    ------------+--------------
              1 |            1 (1 fila)

But this doesn&#39;t work:

```
SELECT nextval(&#39;foo.SQ_ID&#39;);
```

    ERROR:  no existe la relaci&#243;n &#171;foo.sq_id&#187;
    L&#205;NEA 1: SELECT nextval(&#39;foo.SQ_ID&#39;);

What is wrong ?

It says that  not exist the relation `foo.sq_id`, but it exists.






postgresql sequence nextval in schema

How can I **list all the tables** of a PostgreSQL database and **order them by size**?

postgresql list and order tables by size

I have a materialized view on a PostgreSQL 9.3 database which seldom changes (about twice a day). But when it does, I&#39;d like to update its data promptly.

Here is what I was thinking about so far:

There is a materialized view `mat_view` which gets its data from tables `table1` and `table2` using some join statement.

Whenever something in `table1` or `table2` changes, I already have a trigger which updates a little configuration table `config` consisting of

    table_name | mat_view_name | need_update
    -----------+---------------+------------
    table1     | mat_view      | TRUE/FALSE
    table2     | mat_view      | TRUE/FALSE

So if anything in `table1` changes (there&#39;s a trigger on UPDATE and on DELETE for every statement), the field `need_update` in the first row is set to `TRUE`.
The same goes for `table2` and the second row.

Obviously, if `need_update` is TRUE, then the materialized view must be refreshed.

**UPDATE**:
Since materialized views do not support rules (as @pozs mentioned in a comment below), I would go one step further. I&#39;d create a dummy view `v_mat_view` with the definition &quot;`SELECT * FROM mat_view`&quot;. When the user does a SELECT on this view, I need to create a rule ON SELECT which does the following:

 - check whether `mat_view` should be updated (`SELECT 1 FROM config WHERE mat_view_name=&#39;mat_view&#39; AND need_update=TRUE`)
 - reset the `need_update` flag with `UPDATE config SET need_update=FALSE where mat_view_name=&#39;mat_view&#39;`
 - `REFRESH MATERIALIZED VIEW mat_view`
 - and at last do the original SELECT statement but with `mat_view` as the target.

**UPDATE2**:
I tried creating the steps above:

Create a function that handles the four points mentioned above:

    CREATE OR REPLACE FUNCTION mat_view_selector()
    RETURNS SETOF mat_view AS $body$
    BEGIN
      -- here is checking whether to refresh the mat_view
      -- then return the select:
      RETURN QUERY SELECT * FROM mat_view;
    END;
    $body$ LANGUAGE plpgsql;
    
Create the view `v_mat_view` which really selects from the function `mat_view_selector`:

    CREATE TABLE v_mat_view AS SELECT * from mat_view LIMIT 1;
    DELETE FROM v_mat_view;
    
    CREATE RULE &quot;_RETURN&quot; AS
        ON SELECT TO v_mat_view
        DO INSTEAD 
            SELECT * FROM mat_view_selector();
        -- this also converts the empty table &#39;v_mat_view&#39; into a view.

The result is unsatisfying:
---------------------------

    # explain analyze select field1 from v_mat_view where field2 = 44;
    QUERY PLAN
    Function Scan on mat_view_selector (cost=0.25..12.75 rows=5 width=4)
    (actual time=15.457..18.048 rows=1 loops=1)
    Filter: (field2 = 44)
    Rows Removed by Filter: 20021
    Total runtime: 31.753 ms

in comparison to selecting from the mat_view itself:

    # explain analyze select field1 from mat_view where field2 = 44;
    QUERY PLAN
    Index Scan using mat_view_field2 on mat_view (cost=0.29..8.30 rows=1 width=4)
      (actual time=0.015..0.016 rows=1 loops=1)
    Index Cond: (field2 = 44)
    Total runtime: 0.036 ms

So essentially it DOES work, but performance might be an issue.

Anyone have better ideas?
If not, then I would have to implement it somehow in the application logic or worse: run a simple cronjob that runs every minute or so.

Content Type	Original Author	Original Content on Stackoverflow
Question	rlib	View Question on Stackoverflow
Solution 1 - Json	rlib	View Answer on Stackoverflow

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