Oracle trigger if not updating
Oracle trigger if not updating - depression dating sites
The processing is to be done via a trigger so that we get a single, consistent, approach to detecting changed data from multiple client (vendor) software processing.
Below illustrates a crude “sequence” that assigns an incrementing counter to a primary key column: It should be noted that for real “incrementing sequence” behavior, the built-in capabilities of the database should normally be used, which may include sequence objects or other autoincrementing capabilities.The above SQL functions are usually executed “inline” with the INSERT or UPDATE statement being executed, meaning, a single statement is executed which embeds the given expressions or subqueries within the VALUES or SET clause of the statement.Although in some cases, the function is “pre-executed” in a SELECT statement of its own beforehand.For primary key columns, SQLAlchemy will in most cases use these capabilities automatically.See the API documentation for of a statement is an internal SQLAlchemy object which contains all information about the statement being executed, including its source expression, the parameters associated with it and the cursor.Two popular reasons to use compound trigger are: CREATE OR REPLACE TRIGGER compound_trigger_name FOR [INSERT|DELETE]UPDATE [OF column] ON table COMPOUND TRIGGER -- Declarative Section (optional) -- Variables declared here have firing-statement duration.
--Executed before DML statement BEFORE STATEMENT IS BEGIN NULL; END BEFORE STATEMENT; --Executed before each row change- : NEW, : OLD are available BEFORE EACH ROW IS BEGIN NULL; END BEFORE EACH ROW; --Executed aftereach row change- : NEW, : OLD are available AFTER EACH ROW IS BEGIN NULL; END AFTER EACH ROW; --Executed after DML statement AFTER STATEMENT IS BEGIN NULL; END AFTER STATEMENT; END compound_trigger_name; Hopefully this example with make things more clear. SALARY IS NULL) ) THEN v_index := v_index 1; v_emp_changes(v_index).upd_dt := SYSDATE; v_emp_changes(v_index).upd_by := SYS_CONTEXT ('USERENV', 'SESSION_USER'); v_emp_changes(v_index).emp_id := : NEW.emp_id; v_emp_changes(v_index).field := 'SALARY'; v_emp_changes(v_index).from_value := to_char(: OLD.
This happens when all of the following is true: Whether or not the default generation clause “pre-executes” is not something that normally needs to be considered, unless it is being addressed for performance reasons.
When the statement is executed with a single set of parameters (that is, it is not an “executemany” style execution), the returned is similar to that of a regular SQL default; if it’s placed on a primary key column for a database which doesn’t have a way to “postfetch” the ID, and the statement is not “inlined”, the SQL expression is pre-executed; otherwise, SQLAlchemy lets the default fire off on the database side normally. This is becaue the “post-fetch” operation requires that the primary key value already be available, so that the row can be selected on its primary key.
With the compound trigger, both the statement-level and row-level action can be put up in a single trigger.
Plus there is an added advantage: it allows sharing of common state between all the trigger-points using variable.
It is most commonly used in conjunction with a single integer primary key column: Where above, the table “cartitems” is associated with a sequence named “cart_id_seq”.