Double quotes are for names of tables or fields. Sometimes You can omit them. The single quotes are for string constants. This is the SQL standard. In the verbose form, your query looks like this:

    select * from &quot;employee&quot; where &quot;employee_name&quot;=&#39;elina&#39;;

As explained in [the PostgreSQL manual](https://www.postgresql.org/docs/current/static/sql-syntax-lexical.html#SQL-SYNTAX-STRINGS):

&gt; A string constant in SQL is an arbitrary sequence of characters bounded by single quotes (`&#39;`), for example `&#39;This is a string&#39;`. To include a single-quote character within a string constant, write two adjacent single quotes, e.g., `&#39;Dianne&#39;&#39;s horse&#39;`. Note that this is not the same as a double-quote character (`&quot;`).

Elsewhere [on the same page](https://www.postgresql.org/docs/current/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS):

&gt; There is a second kind of identifier: the *delimited identifier* or *quoted identifier*. It is formed by enclosing an arbitrary sequence of characters in double-quotes (`&quot;`). A delimited identifier is always an identifier, never a key word. So `&quot;select&quot;` could be used to refer to a column or table named &quot;select&quot;, whereas an unquoted `select` would be taken as a key word and would therefore provoke a parse error when used where a table or column name is expected.

TL;DR: Single quotes for string constants, double quotes for table/column names.

Well single quotes are used for string literals and double quotes are used for escaping DB objects like table name / column name etc.

Specifically, double quotes are used for escaping a column/table name if it&#39;s resemble to any reserve/key word. Though every RDBMS have their own way of escaping the same (like backtique in `MySQL` or square bracket in `SQL Server`) but using double quotes is ANSI standard.

Is there a way to disable the ctrl-click &#39;peek&#39; feature in Visual Studio Code? Ideally I&#39;d like ctrl-click to just open the file containing the definition in a new tab.

**Edit**: I submitted [an issue](https://github.com/Microsoft/vscode/issues/31046) to at least make it less confusing. Apparently my terminology is slightly wrong.

To clarify, there are two actions:

1. Right-click -&gt; **Peek Definition**
2. Right-click -&gt; **Go to Definition** (bound to ctrl-click)

Their behaviour is as follows:

1. PD, Single Definition
- Opens inline interface showing definition.
2. PD, Multiple Definitions
- Opens inline interface showing definitions.

3. GtD, Single Definition
- Open the file containing the definition.
4. GtD, Multiple Definitions
- Pick one of the definitions at random, open that file, *and* an inline interface showing all the definitions.

All of those are fine except the last. Doing both things results in a really redundant and confusing UI like this:

[![Confusing!][1]][1]

There should be a way to have one of these behaviours:

- Pick one of the definitions at random, open that file.

Or:

- Open inline interface showing all the definitions (*in the current file*)




  [1]: https://i.stack.imgur.com/wqysP.png

Disable peek in Visual Studio Code

[![enter image description here][1]][1]
I searched around the net and the solutions are too complicated. Is there any easy way to get rid of the &quot;Welcome Guide&quot; Screen?


  [1]: https://i.stack.imgur.com/HRxyT.png

How to get rid of Atom&#39;s Welcome screen

I am new to PostgresSQL.I tried 

    select * from employee where employee_name=&quot;elina&quot;;

But that results error as follows:

    ERROR: column &quot;elina&quot; does not exist.
Then I tried by replacing double quotes with single quotes as follows:

    select * from employee where employee_name=&#39;elina&#39;;

It result fine..So what is the difference between single quotes and double quotes in postgresql.If we can&#39;t use double quotes in postgres query,then if any other use for this double quotes in postgreSQL?

What is the difference between single quotes and double quotes in PostgreSQL?

I am new to PostgresSQL.I tried
<pre><code class="hljs language-csharp">select * from employee where employee_name="elina";
</code></pre>
But that results error as follows:
<pre><code class="hljs language-sql">ERROR: column "elina" does not exist.
</code></pre>
Then I tried by replacing double quotes with single quotes as follows:
<pre><code class="hljs language-csharp">select * from employee where employee_name='elina';
</code></pre>
It result fine..So what is the difference between single quotes and double quotes in postgresql.If we can't use double quotes in postgres query,then if any other use for this double quotes in postgreSQL?

I&#39;m writing a `Java` application to automatically build and run SQL queries. For many tables my code works fine but on a certain table it gets stuck by throwing the following exception:

    Exception in thread &quot;main&quot; org.postgresql.util.PSQLException: ERROR: column &quot;continent&quot; does not exist
      Hint: Perhaps you meant to reference the column &quot;countries.Continent&quot;.
      Position: 8

The query that has been run is the following:

    SELECT Continent
    FROM network.countries
    WHERE Continent IS NOT NULL
    AND Continent &lt;&gt; &#39;&#39;
    LIMIT 5

This essentially returns `5` non-empty values from the column.

I don&#39;t understand why I&#39;m getting the &quot;column does not exist&quot; error when it clearly does in [pgAdmin 4][1]. I can see that there is a schema with the name `Network` which contains the table `countries` and that table has a column called `Continent` just as expected.

Since all column, schema and table names are retrieved by the application itself I don&#39;t think there has been a spelling or semantical error so why does [PostgreSQL][2] cause problems regardless? Running the query in pgAdmin4 nor using the suggested `countries.Continent` is working.

My PostgreSQL version is the newest as of now:

    $ psql --version
    psql (PostgreSQL) 9.6.1

How can I successfully run the query?

  [1]: https://www.pgadmin.org/download/windows4.php
  [2]: https://www.postgresql.org/

PostgreSQL &quot;Column does not exist&quot; but it actually does

Consider:

    ./mysqladmin -u root -p** &#39;_redacted_&#39;  

Output (including typing the password):

&gt; Enter password: 
&gt;
&gt; mysqladmin: connect to server at &#39;localhost&#39; failed error:  
&gt; **&#39;Access denied for user &#39;root&#39;@&#39;localhost&#39; (using password: YES)&#39;**

How can I fix this?


MySQL Error: : &#39;Access denied for user &#39;root&#39;@&#39;localhost&#39;

I would like to include null values in an Apache Spark join.  Spark doesn&#39;t include rows with null by default.

Here is the default Spark behavior.

&lt;!-- language: scala --&gt;

    val numbersDf = Seq(
      (&quot;123&quot;),
      (&quot;456&quot;),
      (null),
      (&quot;&quot;)
    ).toDF(&quot;numbers&quot;)
    
    val lettersDf = Seq(
      (&quot;123&quot;, &quot;abc&quot;),
      (&quot;456&quot;, &quot;def&quot;),
      (null, &quot;zzz&quot;),
      (&quot;&quot;, &quot;hhh&quot;)
    ).toDF(&quot;numbers&quot;, &quot;letters&quot;)
    
    val joinedDf = numbersDf.join(lettersDf, Seq(&quot;numbers&quot;))

Here is the output of `joinedDf.show()`:


&lt;!-- language: none --&gt;

    +-------+-------+
    |numbers|letters|
    +-------+-------+
    |    123|    abc|
    |    456|    def|
    |       |    hhh|
    +-------+-------+

This is the output I would like:


&lt;!-- language: none --&gt;

    +-------+-------+
    |numbers|letters|
    +-------+-------+
    |    123|    abc|
    |    456|    def|
    |       |    hhh|
    |   null|    zzz|
    +-------+-------+

Including null values in an Apache Spark Join

I&#39;m getting the following error when doing the following type of insert:

Query:

    INSERT INTO accounts (type, person_id) VALUES (&#39;PersonAccount&#39;, 1) ON
    CONFLICT (type, person_id) WHERE type = &#39;PersonAccount&#39; DO UPDATE SET
    updated_at = EXCLUDED.updated_at RETURNING *

Error:

&gt; SQL execution failed (Reason: ERROR: there is no unique or exclusion
&gt; constraint matching the ON CONFLICT specification)

I also have an unique INDEX:

    CREATE UNIQUE INDEX uniq_person_accounts ON accounts USING btree (type,
    person_id) WHERE ((type)::text = &#39;PersonAccount&#39;::text);

The thing is that sometimes it works, but not every time. I *randomly* get
that exception, which is really strange. It seems that it can&#39;t access that
INDEX or it doesn&#39;t know it exists.

Any suggestion?

I&#39;m using PostgreSQL 9.5.5.

Example while executing the code that tries to find or create an account:

    INSERT INTO accounts (type, person_id, created_at, updated_at) VALUES (&#39;PersonAccount&#39;, 69559, &#39;2017-02-03 12:09:27.259&#39;, &#39;2017-02-03 12:09:27.259&#39;) ON CONFLICT (type, person_id) WHERE type = &#39;PersonAccount&#39; DO UPDATE SET updated_at = EXCLUDED.updated_at RETURNING *
     SQL execution failed (Reason: ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification)

In this case, I&#39;m sure that the account does not exist. Furthermore, it never outputs the error when the person has already an account. The problem is that, in some cases, it also works if there is no account yet. The query is exactly the same. 

No unique or exclusion constraint matching the ON CONFLICT

I have a table with a column `ctime` of type `time without time zone`. 

      |   cdate    |  ctime   
      +------------+----------
      | 2016-12-24 | 12:02:17
      | 2016-12-24 | 12:02:32
      | 2016-12-24 | 12:03:00
      | 2016-12-24 | 12:02:10

I would like to group by both `cdate` and `ctime` but would like for `ctime` to count only hours.

how do I group by by hour in postgresql with a &quot;time&quot; field?

I exported a postgresql database from an external server, and attempted to import it into my local server but got this error:

    unrecognized configuration parameter &quot;idle_in_transaction_session_timeout&quot;

Does this kind of error mean that the two servers are using different versions of postgresql? I looked into that, and the external server is running:

    version
    PostgreSQL 9.5.4 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2, 64-bit	

and my server is running:

    version
    PostgreSQL 9.5.5 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609, 64-bit	

Pretty much the same thing. Is there a site where you can see all of the valid config parameters for each version? And is there a way to sync up two databases like this, so incompatibilities like this get patched up automatically?

Postgresql - unrecognized configuration parameter

My docker compose file has three containers, web, nginx, and postgres. Postgres looks like this:

    postgres:
      container_name: postgres
      restart: always
      image: postgres:latest
      volumes:
        - ./database:/var/lib/postgresql
      ports:
        - 5432:5432

My goal is to mount a volume which corresponds to a local folder called `./database` inside the postgres container as `/var/lib/postgres`. When I start these containers and insert data into postgres, I verify that `/var/lib/postgres/data/base/` is full of the data I&#39;m adding (in the postgres container), but in my local system, `./database` only gets a `data` folder in it, i.e. `./database/data` is created, but it&#39;s empty. Why? 

Notes:

- [This suggests my above file should work.](https://github.com/docker/compose/issues/2971)
- [This person is using docker services which is interesting](https://stackoverflow.com/questions/39175194/docker-compose-persistent-data-mysql)

### UPDATE 1

Per Nick&#39;s suggestion, I did a `docker inspect` and found: 

        &quot;Mounts&quot;: [
            {
                &quot;Source&quot;: &quot;/Users/alex/Documents/MyApp/database&quot;,
                &quot;Destination&quot;: &quot;/var/lib/postgresql&quot;,
                &quot;Mode&quot;: &quot;rw&quot;,
                &quot;RW&quot;: true,
                &quot;Propagation&quot;: &quot;rprivate&quot;
            },
            {
                &quot;Name&quot;: &quot;e5bf22471215db058127109053e72e0a423d97b05a2afb4824b411322efd2c35&quot;,
                &quot;Source&quot;: &quot;/var/lib/docker/volumes/e5bf22471215db058127109053e72e0a423d97b05a2afb4824b411322efd2c35/_data&quot;,
                &quot;Destination&quot;: &quot;/var/lib/postgresql/data&quot;,
                &quot;Driver&quot;: &quot;local&quot;,
                &quot;Mode&quot;: &quot;&quot;,
                &quot;RW&quot;: true,
                &quot;Propagation&quot;: &quot;&quot;
            }
        ],


Which makes it seem like the data is being stolen by another volume I didn&#39;t code myself. Not sure why that is. Is the postgres image creating that volume for me? If so, is there some way to use *that volume* instead of the volume I&#39;m mounting when I restart? Otherwise, is there a good way of disabling that other volume and using my own, `./database`?

### UPDATE 2 

I found the solution, thanks to Nick! (and another friend) Answer below.


Content Type	Original Author	Original Content on Stackoverflow
Question	jisna	View Question on Stackoverflow
Solution 1 - Sql	Michas	View Answer on Stackoverflow
Solution 2 - Sql	melpomene	View Answer on Stackoverflow
Solution 3 - Sql	Rahul	View Answer on Stackoverflow

What is the difference between single quotes and double quotes in PostgreSQL?

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How to get rid of Atom's Welcome screen

Disable peek in Visual Studio Code

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