I want to count rows created/inside (dont know what it is called) a trigger.
like i have a trigger :
CREATE
DEFINER=`root`#`localhost`
TRIGGER `mydb`.`tn_air_staff_leave_application`
AFTER INSERT ON `mydb`.`staff_leave_application`
FOR EACH ROW
BEGIN
----
----
----
END$$
and want to know how many rows trigger is going to create, I need this value inside trigger:
set #newrows:= (select count(*) from tn_air_staff_leave_application);
is it possible?? if not any other solution out there???
A trigger is a purely passive piece of code which is executed before or after a row is inserted, updated or deleted from a table in your database.
The trigger can not be executed actively anc thus does not have a return value you can read.
What you can do is to let your trigger write a value into another table or into a session variable which then can be queried for in an extra query.
You can not store a whole result row or a result set of several rows into a session variable like you are trying in your example.
In MySQL the trigger is always executed FOR EACH ROW, means within the trigger you will only look at one row, not at several.
EDIT:
Actually your example query returns a single value, so this would work. (would deliver the amount of total records in your tn_air_staff_leave_application table into the local session variable #newrows)
For more specific help you would need to be more specific on what you're trying to do
Related
Wanting to CONCAT two columns to make a new ID, as per the image.
Desired result
The Trigger statement I have is: And I have tried Trigger INSERT and UPDATE events.
Trigger statement
SET new.img_url_id = CONCAT(new.img_metadata_id, new.mag_name_id)
The Trigger statement returns values in the 'mag_name_id' field (10). The Trigger has to happen after field 'img_metadata_id' is inserted because 'img_metadata_id' is auto-incremented, and after 'mag_name_id' is inserted, it's pulled from another table. Changing the Trigger time to After, PHPMyAdmin gives an error. Do I need to do a Procedure?
Thanks.
I have a table on a mysql 5.7 db, containing say athletes with their mean, max, avg times in a specific sport. I have another table that lists some calculated statistics based on those values.
I managed to do the calculcations that end up on the second using stored procedures. I use as input parameter to the stored procedure the athlete's name.
So when in the first table, an athlete is inserted (with his/her avg/min/max times) or his/her values are updated and I run the stored procedure, the later updates the statistics table.
My question is how to achieve the same result with triggers?
I guess it is feasible/easy to update the entire table on each insert or update of the first table. What would be more efficient performance-wise, would be on each :
INSERT into table1 values (..) where athlete_name="John Do"
(...)
ON DUPLICATE KEY UPDATE (...)
Run a trigger in the pseudocode form :
INSERT into statistics_table values (..) where athlete_name="John Do"
ON DUPLICATE KEY UPDATE (...)
How can the the athlete_name="John Do" be passed to the trigger dynamically, to avoid update the entire statistics table?
You cannot pass any parameters to a trigger and the insert statement does not support the where clause either.
Having said this, a trigger can pick up the user's name from the record being inserted / updated / deleted using NEW.athlete_name or OLD.athlete_name (whichever is required) and use that to call a stored procedure:
Within the trigger body, the OLD and NEW keywords enable you to access
columns in the rows affected by a trigger. OLD and NEW are MySQL
extensions to triggers; they are not case-sensitive.
In an INSERT trigger, only NEW.col_name can be used; there is no old
row. In a DELETE trigger, only OLD.col_name can be used; there is no
new row. In an UPDATE trigger, you can use OLD.col_name to refer to
the columns of a row before it is updated and NEW.col_name to refer to
the columns of the row after it is updated.
A column named with OLD is read only. You can refer to it (if you have
the SELECT privilege), but not modify it. You can refer to a column
named with NEW if you have the SELECT privilege for it. In a BEFORE
trigger, you can also change its value with SET NEW.col_name = value
if you have the UPDATE privilege for it. This means you can use a
trigger to modify the values to be inserted into a new row or used to
update a row. (Such a SET statement has no effect in an AFTER trigger
because the row change will have already occurred.)
You can create triggers that fire after each insert or update on the parent table (athletes). Within each trigger, you can access the value of column athlete_name on the record that was just created or changed, and then invoke your stored procedure using CALL().
Here is a code sample for such an INSERT trigger :
CREATE TRIGGER athletes_upd AFTER INSERT ON athletes
FOR EACH ROW
BEGIN
CALL my_procedure(NEW.athlete_name);
END;
UPDATE trigger :
CREATE TRIGGER athletes_upd AFTER UPDATE ON athletes
FOR EACH ROW
BEGIN
CALL my_procedure(NEW.athlete_name); -- or maybe OLD.athlete_name ?
END;
When I insert data in db I have to compare the current record with the previous one. If neccassary, some values of the current record needs to be modified.
I've tried some pieces of SQL like below, but all give SQL errors. This one gives me an error says that I select more than 1 records.
DELIMITER $$
CREATE
TRIGGER set_moment_display
BEFORE INSERT ON data
FOR EACH ROW
BEGIN
DECLARE moment DATETIME;
SELECT press_moment_1 INTO moment FROM data LIMIT 1;
IF moment > NEW.press_moment_1 THEN SET NEW.press_moment_1 = moment;
END IF;
END$$
DELIMITER ;
How do I achieve what I've described above.
The problem here is that, since a SQL database has no implicit concept of row ordering (you supply the ordering criteria on every query), there is no "previous" row for the trigger to look at. The "previously inserted row" has no meaning in the context of an insert trigger.
Suppose for a moment that it did and there were several processes inserting rows in the table. When the trigger fired for process #1's insert, which row is the "previous" row? The one previously inserted by process #1? Suppose the chronologically "most recent" row was actually inserted by process #3?
If you need to do this it cannot be done in a trigger unless you can use a know key value to identify the row you understand as "most recent". Otherwise it must be handled in the application that is doing the inserts.
You can use the alias "OLD."
You can refer to columns in the subject table
(the table associated with the trigger) by using the aliases OLD and NEW.
OLD.col_name refers to a column of an existing row before
it is updated or deleted. NEW.col_name refers to the column
of a new row to be inserted or an existing row after it is updated
UPDATE
Jim Garrison properly pointed up to me the mistake, "BEFORE INSERT" doesn't have "OLD." values, this alias works only for UPDATE and DELETE.
I'm trying to find the most effecient way of inserting data into another table when a particular field is updated on trigger table. The INSERT should only occur on a specific type of update.
The table on which I want to create the trigger is named incremental. The table I'm inserting into is named crm_record
On incremental there is a field called status. By default when a record is initially added to the table the status field is set to new. After billing has processed that value changes to processed. So once this occurs I want to INSERT into crm_record, only if the value of another field (success) is set to 1.
I have considered using both CASE and IF but would like an expert's opinion on the best way to do this.
Ok, I eventually went with this that seemed to work. Thanks for pointing me in the right direction
CREATE TRIGGER `incremental5_after_ins_tr_crmm` AFTER UPDATE ON `incremental5`
FOR EACH ROW
BEGIN
IF Status = 'processed' AND Success = 1 THEN
INSERT INTO crm_master (msisdn,source,contract_type,revenue) VALUE (new.msisdn,'INC5',new.contract_type,revenue=revenue+2.5)
ON DUPLICATE KEY UPDATE contract_type=new.contract_type,revenue=revenue+2.5;
END IF;
END;
All you need to do is to create an AFTER UPDATE trigger and test the value of status and success together. If it's going only going to be one state you're testing for then an IF statement would be the simplest way to go about it.
However before implementing a trigger it's always worth going back a step and checking to see if the row in crm_record shouldn't actually be inserted via the code logic when the status and success columns are updated.
Is it possible to check whether a particular value in a column exists in other databases using trigger? These two databases are located inside the same MYSQL instance. Specifically, what I want to do is this:
Before a row is added to a table ( Document_Index_table) inside Database A ( Document_DB).
A trigger is fired. This trigger carries the one of the column value (usr_id) inside the row and pass it to Database B ( User_Control_DB).
Based on the values, User_Control_DB will check whether the usr_id exists in column usr_id of the table (Usr_Information).
If exists, then return a true to Document_DB and the row in 1. is allowed to add to the Document_DB.
If not, then an error is issued. No row is added to Document_DB.
How can this be done, if it can be done at all?
Edit: Both databases are MySQL databases
So, I'm a complete novice at database development, but you could do something like this:
Create a 'Before' insert trigger on your document_index_table.
The trigger does something like this:
declare numRows integer;
select count(*) from user_control_db.usr_information where usr_id = NEW.usr_id into num_rows;
if (numRows > 0) then
call NonExistentProc();
end if;
I believe that this would accomplish what you wanted. It'll produce an error like "PROCEDURE documentdb.NonExistenProc does not exist" and skip the insert if there isn't at least one row that has the matching usr id in the user control db.
Again, I'm a novice at this DB stuff so there might be a more elegant way, but this worked for my single test case.
Hope that helps.