Getorgchart ajax foreign key10/30/2022 ![]() ![]()
You should ask your colleague for his reasons for preferring triggers. This probelm can be circumvented by declaring the foreign key, but then disabling it, using ALTER TABLE NOCHECK CONSTRAINT. That doesn't seem a very likely scenario.Īnother drawback of using triggers is that the relationship isn't discoverable by means of system views/tables. THe only reason I can see for doing this is that there are already triggers on the tables doing something very similar, so that changing them to check integrity would add no extra overhead in terms of table access and almost no difference in speed. Both of these will occur (and probably more slowly) when you se a trigger to enforce ref. The reason for timeouts from FKs is (1) the lock placed on the primary key table to check the data values, and (2) the extra time for which locks may be held on other tables while the integrity is being checked. integrity), there is no point at all in simply reproducing the same functionality using a trigger. integrity constraints (to be balanced against the risk of loss of ref. While there is of course a performance advantage to removing ref. However, if you want to enforce cascade update/delete operations in SQL 7-, or to enforce integrity across databases, you would need to use a trigger instead of a FK. I can't imagine that that could be more efficient. But you will effectively be rewriting Sybase/MS C (or whatever it is) code, using T-SQL. You can precisely replicate the functionality of a FK constraint using a trigger. In such cases, using integrity constraints eliminates the performance overhead incurred by this transmission. Since your applications use SQL, they cannot achieve this level of optimization.Įnforcing business rules with SQL statements can be even more costly in a networked environment because the SQL statements must be transmitted over a network. The semantics of integrity constraints are very clearly defined, so the internal operations that Oracle performs to enforce them are optimized beneath the level of SQL statements in Oracle. I don't know about you but it makes perfect sense to me.Įnforcing rules with integrity constraints is less costly than enforcing the equivalent rules by issuing SQL statements in your application. Here's another reference to Oracle8 for enforcing business rules to your DB through integrity constraints (foreign keys). Sorry, I don't agree with using triggers in place of foreign keys. ![]() Getorgchart ajax foreign key update#For example, creating an AFTER UPDATE statement trigger on the EMP table that itself issues an UPDATE statement on EMP causes the trigger to fire recursively until it has run out of memory. * Be careful not to create recursive triggers. ![]() Getorgchart ajax foreign key code#If the logic for your trigger requires much more than 60 lines of PL/SQL code, it is better to include most of the code in a stored procedure, and call the procedure from the trigger. ![]() * Limit the size of triggers (60 lines or fewer is a good guideline). For example, do not define triggers to enforce data integrity rules that can be easily enforced using declarative integrity constraints. * Do not define triggers that duplicate the functionality already built into Oracle. * Use database triggers only for centralized, global operations that should be fired for the triggering statement, regardless of which user or database application issues the statement. * Use triggers to guarantee that when a specific operation is performed, related actions are performed. Use the following guidelines when designing triggers: Whatever happened to those ERDs (for Frank, Entity Relationship Diagrams) and UML (Universal Modeling Language) Class Diagrams? Do they just get thrown out the window in the physical DB Design phase? Here's a direct quote from the Oracle8 Server Application Developer's Guide Second: If there is NO merit to what he says, can anyone suggest some simple demos to illustrate that fact to him?įoreign Keys = True Referential Integrity Getorgchart ajax foreign key how to#Foreign-keys are fundamental to all relational DB systems, not just MSSQL - why have them if they are inferior? So, I need to either find out he's right (unlikely), or find out how to present to him the facts so that he doesn't go making insane redesigns to our current system.įirst: Is there any merit to what he says? Can straight-forward FKs cause timeouts? How significant is the timeout risk? How best to mitigate this issue? If foreign-keys were inferior to triggers, imagine there would be an immense number of articles on sources like trumpeting that fact. He says that building triggers in all the places where referencial data integrity is needed is the best solution. I have a new collegue who insists that foreign-keys are evil, and are a major source of deadlocks. (This may have been asked before, and if so, please just point me to the right place.) ![]()
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