Oracle-L: RE: SQL question

From: Rick Stephenson <RStephenson_at_Ovid.com>
Date: Mon, 24 Feb 2003 12:54:19 -0800
Message-ID: <F001.00557610.20030224125419@fatcity.com>

Sorry, I guess I could have been a little more clear.

Another example:

Table Employee:
Emp_id number primary key -- generated with a sequence Emp_name varchar2(20) unique

Table Employee_log:
  Emp_id number primary key
  Time_stamp date primary key
  Emp_stats varchar2(50)

A process receives the employee name, and other information that needs to be stored in the table employee_log. The process needs to retrieve the emp_id from the employee table, so it does a lookup. If the employee exists, the emp_id is retrieved and the information is then inserted into the employee_log table. If the employee does not currently exist, a new employee is added to the table employee.

We run into problems when we have many concurrent processes running and more than one process receives the same employee name. They both do a lookup and they both conclude the employee does not exist. Thus, they both try and do an insert into the employee table. One will succeed and the other will fail.

Is there away to avoid this scenario?

I hope I made this a little clearer.

Thanks,

Rick Stephenson

-----Original Message-----
Sent: Monday, February 24, 2003 1:05 PM
To: Multiple recipients of list ORACLE-L

Rick - What about selecting the primary key for your table from a sequence? Oracle will ensure each session receives a unique number.

What is your overall goal?

Dennis Williams
DBA, 40%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Monday, February 24, 2003 1:50 PM
To: Multiple recipients of list ORACLE-L

OS: Solaris 2.8

Database: Oracle 9.2.0.2

Situation in chronological order

Connection A: select * from table A where id = 1; Result: no rows returned
-- This means I need to insert the row, as it does not exists yet.

Connection B: select * from table A where id = 1; Result: no rows returned
-- This means I need to insert the row, as it does not exists yet.

Connection A: insert into table A(id) values = 1; Result: 1 row inserted

Connection B: insert into table A(id) values = 1; Result: Unique constraint violated -- This is the problem. How do I avoid this happening?

Question: How can I force connection B to wait for connection A to insert the new row before it does the select?

If I were updating the row, I could use the "for update" clause to force the wait. Is there a clean way to do that for an insert?

Thanks for your help,

Rick Stephenson

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Author: DENNIS WILLIAMS
INET: DWILLIAMS_at_LIFETOUCH.COM

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Author: Rick Stephenson
INET: RStephenson_at_Ovid.com

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