Databases
StackOverflow2013
Postsdbo
POCan a SQL Case statment be used to test if a Join statement should be used?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POCan a SQL Case statment be used to test if a Join statement should be used?
    primarykey
    data
    text
    <p>What I am trying to do, using java, is:</p> <ul> <li>access a database</li> <li>read a record from table "Target_stats"</li> <li>if the field "threat_level" = 0, doAction1</li> <li>if the field "threat_level" > 0, get additional fields from another table "Attacker_stats" and doAction2</li> <li>read the next record</li> </ul> <p>Now I have everything I need but a well thought out SQL statement that will allow me to only go through the database only once, if this does not work I suspect I will need to use two separate SQL statements and go through the database a second time. I do not have a clear understanding of case statements, so I will just provide pseudo code using an if statement.</p> <pre><code>SELECT A.1, A.2, A.3 if(A.3 &gt; 0){ SELECT A.1, A.2, A.3, B.1, B.3 FROM A JOIN B ON A.1 = B.1 } FROM A </code></pre> <p>Can anyone shed any light on my situation? </p> <p>EDIT: Thankyou both for your time and effort. I understand both of your comments and I believe that I am headed more towards the right direction however, I'm still having some trouble. I didn't know about SQLfiddle before so I have now gone ahead and made a sample DB and tried to demonstrate my purpose. Here is the link: <a href="http://sqlfiddle.com/#!3/ea108/1" rel="nofollow">http://sqlfiddle.com/#!3/ea108/1</a> What I want to do here is Select target_stats.server_id, target_stats.target, target_stats.threat_level Where interval_id=3 and if the threat_level>0 I want to retrieve attack_stats.attacker, attack_stats.sig_name Where interval_id=3. Again, thankyou for your time and effort it is very useful to me</p> <p>EDIT: after some tinkering around, I figured it out. thankyou so much for your help</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USexit_1
    1. USexit_1
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COSQL is *not* procedural code. If there are two different "actions" as you state, your intent may be clearer to someone reading your code if there are two distinct queries. I don't know how complex these queries are, but if they are as simple as the example suggests, the db hit probably won't even make a noticeable performance difference. Purely speculation, but just a thought...
      singulars
      1. POCan a SQL Case statment be used to test if a Join statement should be used?
      1. USOcelot20
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload