Yes it stops execution so this is generally preferable to `HAVING COUNT(*) &gt; 0` which often won&#39;t.

With `EXISTS` if you look at the execution plan you will see that the actual number of rows coming out of `table1 ` will not be more than 1 irrespective of number of matching records.

In some circumstances SQL Server can convert the tree for the `COUNT` query to the same as the one for `EXISTS` during the simplification phase (with a semi join and no aggregate operator in sight) [an example of that is discussed in the comments here][1].

For more complicated sub trees than shown in the question you may occasionally find the `COUNT` performs better than `EXISTS` however. Because the semi join needs only retrieve one row from the sub tree this can encourage a plan with nested loops for that part of the tree - which may not work out optimal in practice.


  [1]: 
https://web.archive.org/web/20190319012047/http://sqlblog.com/blogs/andrew_kelly/archive/2007/12/15/exists-vs-count-the-battle-never-ends.aspx

There&#39;s no need for &quot;else&quot; in this case:

    IF EXISTS(SELECT *  FROM  table1  WHERE Name=&#39;John&#39; ) return 1
    return 0

&gt; **Possible Duplicate:**  
&gt; [Python: Sort a dictionary by value](https://stackoverflow.com/questions/613183/python-sort-a-dictionary-by-value)  

&lt;!-- End of automatically inserted text --&gt;

I have a dictionary like this:
    
    A = {&#39;Name1&#39;:34, &#39;Name2&#39;: 12, &#39;Name6&#39;: 46,....}

I want a list of keys sorted by the values, i.e. `[Name2, Name1, Name6....]`

Thanks!!!

sort values and return list of keys from dict python

There are way too many questions and answers about this basic functionality, I cannot see the wood for the trees. 

In Java there is only one simple answer (`java.text.NumberFormat` and its subclasses) so I&#39;m sure the majority of plugins, questions and answers will mature eventually to a de-facto standard for JQuery.

**This plugin** is the best I found so far, but I don&#39;t know if it&#39;s still developed, is mature etc.

http://plugins.jquery.com/project/numberformatter

Is there a better solution? Is it mature / active enough to rely on?


----------

**Edit:**

I would like to be able to format currencies, decimal, integers based on the same format patterns Java uses, so that data recieved on the client side can be formatted without sending it first to the server. 

e.g. 

Format `1000` to `$1,000` or `1,000.00` etc (locale support is nice)

Seems that http://plugins.jquery.com/project/numberformatter does the job but the question was: &quot;Am I using the right thing?&quot; or &quot;Is there a better way to do so?&quot;





JQuery Number Formatting

If we have a `SELECT` statement inside an `IF EXISTS`, does the execution stop as soon as it finds a record in the table? For example:


    IF EXISTS(SELECT *  FROM  table1  WHERE Name=&#39;John&#39; )
    
    return 1
    
    else
    
    return 0

If a row exists in the table with the name = John, does it stops execution and returns 1 or does it traverses through the entire table looking for more matches?

 

IF EXISTS in T-SQL

If we have a <code>SELECT</code> statement inside an <code>IF EXISTS</code>, does the execution stop as soon as it finds a record in the table? For example:
<pre><code class="hljs language-sql">IF EXISTS(SELECT * FROM table1 WHERE Name='John' )

return 1

else

return 0
</code></pre>
If a row exists in the table with the name = John, does it stops execution and returns 1 or does it traverses through the entire table looking for more matches?

I have table like this:

    a          b
    1          23
    1          2
    1          7
    2          9
    2          11

I want to select the first row(order does not matter) from a &quot;GROUP BY a&quot; query , the result should be

    a          b
    1          23
    2          9

I am using SQL SERVER 2008 how to write the query for this?


sql server select first row from a group

What is best practice for handling the dropping of a temp table.  I have read that you should explicitly handle the drop and also that sql server should handle the drop....what is the correct method? I was always under the impression that you should do your own clean up of the temp tables you create in a sproc, etc.  But, then I found other bits that suggest otherwise.

Any insight would be greatly appreciated.  I am just concerned I am not following best practice with the temp tables I create. 

Thanks,

S

Explicitly drop temp table or let SQL Server handle it

In Microsoft SQL Server how can I get a query execution plan for a query / stored procedure?

How do I obtain a Query Execution Plan in SQL Server?

I am using [Entity Framework][1], and I am inserting records into our database which include a blob field. The blob field can be up to 5&amp;nbsp;MB of data.

When inserting a record into this table, does it lock the whole table?

So if you are querying any data from the table, will it block until the insert is done (I realise there are ways around this, but I am talking by default)?

How long will it take before it causes a deadlock? Will that time depend on how much load is on the server, e.g. if there is not much load, will it take longer to cause a deadlock?

Is there a way to monitor and see what is locked at any particular time?

If each thread is doing queries on single tables, is there then a case where blocking can occur? So isn&#39;t it the case that a deadlock can only occur if you have a query which has a join and is acting on multiple tables?

This is taking into account that most of my code is just a bunch of select statements, not heaps of long running transactions or anything like that.

  [1]: http://en.wikipedia.org/wiki/ADO.NET_Entity_Framework


Does inserting data into SQL Server lock the whole table?

Need to alter a table to allow nulls on a column -- but cant drop the column...can I do this?  Was trying something like:

    ALTER TABLE myTable MODIFY myColumn NULL;

But to no avail....


Can I change a column from NOT NULL to NULL without dropping it?

I know that multiple parameters can be passed to `COALESCE`, but  when you want to to 
check just one expression to see if it doesn&#39;t exist, do you use a default or is it a better practice to use `ISNULL` instead? 

Is there any performance gain between the two?


Using ISNULL vs using COALESCE for checking a specific condition?

At any time in the past, if someone had asked me the maximum size for a `varchar(max)`, I&#39;d have said 2GB, or looked up a more exact [figure][1] (2^31-1, or 2147483647).

However, in some recent testing, I discovered that `varchar(max)` variables can apparently exceed this size:

    create table T (
    	Val1 varchar(max) not null
    )
    go
    declare @KMsg varchar(max) = REPLICATE(&#39;a&#39;,1024);
    declare @MMsg varchar(max) = REPLICATE(@KMsg,1024);
    declare @GMsg varchar(max) = REPLICATE(@MMsg,1024);
    declare @GGMMsg varchar(max) = @GMsg + @GMsg + @MMsg;
    select LEN(@GGMMsg)
    insert into T(Val1) select @GGMMsg
    select LEN(Val1) from T

Results:

    (no column name)
    2148532224
    (1 row(s) affected)
    Msg 7119, Level 16, State 1, Line 6
    Attempting to grow LOB beyond maximum allowed size of 2147483647 bytes.
    The statement has been terminated.
    
    (no column name)
    (0 row(s) affected)

So, given that I now know that a *variable* can exceed the 2GB barrier - does anyone know what the actual limit is for a `varchar(max)` variable?

---

(Above test completed on SQL Server 2008 (not R2). I&#39;d be interested to know whether it applies to other versions)

  [1]: http://msdn.microsoft.com/en-us/library/ms176089.aspx


Maximum size of a varchar(max) variable

How does one cause a delay in execution for a specified number of seconds?

This doesn&#39;t do it:

    WAITFOR DELAY &#39;00:02&#39;;

What is the correct format?


How to wait for 2 seconds?

I want to get only Time from DateTime column using SQL query 
using SQL Server 2005 and 2008
Default output:
    
    AttDate                   
    ==
    2011-02-09 13:09:00    
    2011-02-09 14:10:00    
    
    
I&#39;d like this output:
    
    AttDate                Time 
    ==
    2011-02-09 13:09:00    13:09
    2011-02-09 14:10:00    14:10


How to get Time from DateTime format in SQL?

I have a tableA:
 

    ID value
     1  100
     2  101
     2  444
     3  501

Also TableB 
  

    ID Code
    1
    2

Now I want to populate col = code of table B if there exists ID = 2 in tableA. for multiple values , get max value.
else populate it with &#39;123&#39;. Now here is what I used:

    if exists (select MAX(value) from #A where id = 2)
     BEGIN
     update #B
     set code = (select MAX(value) from #A where id = 2)
     from #A
     END
    
     ELSE 
     
     update #B
     set code = 123
     from #B

I am sure there is some problem in BEGIN;END or in IF EXIST;ELSE.
Basically I want to by-pass the else part if select statement in IF-part exist and vice- versa. For example if select statement of IF=part is:
 

    (select MAX(value) from #A where id = 4)

 It should just populate 123, coz ID = 4 do not exist ! 

SQL Server: IF EXISTS ; ELSE

How do I check whether data in a query exists?

For example:

    users_query = User.query.filter_by(email=&#39;x@x.com&#39;)

How I can check whether users with that email exist?

I can check this with 

    users_query.count()

but how to check it with **exists**?

sqlalchemy exists for query

I changed the datadir of a MySQL installation and all the bases moved correctly except for one. 
I can connect and `USE` the database. `SHOW TABLES` also returns me all the tables correctly, and the files of each table exists on the MySQL data directory.

However, when I try to `SELECT` something from the table, I get an error message that the table does not exist. Yet, this does not make sense since I was able to show the same table through `SHOW TABLES` statement. 

My guess is that `SHOW TABLES` lists file existence but does not check whether a file is corrupted or not. Consequently, I can list those files but not access them.

Nevertheless, it is merely a guess. I have never seen this before. Now, I cannot restart the database for testing, but every other application that uses it is running fine.
But that&#39;s just a guess, I&#39;ve never seen this before. 

Does anyone know why this is happening?

Example:

    mysql&gt; SHOW TABLES;
    +-----------------------+
    | Tables_in_database    |
    +-----------------------+
    | TABLE_ONE             |
    | TABLE_TWO             |
    | TABLE_THREE           |
    +-----------------------+
    mysql&gt; SELECT * FROM TABLE_ONE;
    ERROR 1146 (42S02): Table &#39;database.TABLE_ONE&#39; doesn&#39;t exist



MySQL &gt; Table doesn&#39;t exist. But it does (or it should)

How to select Boolean value from sub query with IF EXISTS statement (SQL Server)?

It should be something like :

    SELECT 
      TABEL1.Id, 
      NewFiled = (IF EXISTS(SELECT Id FROM TABLE2 WHERE TABLE2.ID = TABEL1.ID) 
                     SELECT &#39;TRUE&#39; 
                  ELSE 
                     SELECT &#39;FALSE&#39;) 
    FROM TABEL1

How to use SQL Select statement with IF EXISTS sub query?

I have an `Email` document which has a `sent_at` date field:

    {
      &#39;sent_at&#39;: Date( 1336776254000 )
    }

If this `Email` has not been sent, the `sent_at` field is either null, or non-existant.

I need to get the count of all sent/unsent `Emails`. I&#39;m stuck at trying to figure out the right way to query for this information. I think this is the right way to get the sent count:

    db.emails.count({sent_at: {$ne: null}})

But how should I get the count of the ones that aren&#39;t sent?

Content Type	Original Author	Original Content on Stackoverflow
Question	Sidd	View Question on Stackoverflow
Solution 1 - Sql Server	Martin Smith	View Answer on Stackoverflow
Solution 2 - Sql Server	Miguel	View Answer on Stackoverflow

IF EXISTS in T-SQL

Sql Server Problem Overview

Sql Server Solutions

Solution 1 - Sql Server

Solution 2 - Sql Server

JQuery Number Formatting

sort values and return list of keys from dict python

Attributions