Let`s say I have the following db schema.
user_id (int) email (varchar) phone (varchar)
How to stop executing of insert query if the value of phone is empty. I could do it with script validation, but I`m interesing of mysql solution.
You could write a procedure and use it to validate and insert rows. Or you could write a trigger to check NEW value and throw an exception. To throw the exception you may use SIGNAL statement in MySQL 5.5, or call unknown stored procedure.
For a solution that works completely within mysql, you can use "triggers". This involves:
Defining a mysql stored procedure to perform the validation
Create a trigger to use the validation procedure, e.g. on INSERT
Possibly do something with the error message if validation fails.
For a complete example, take a look at Roland Bouman's blog
Related
(NOTE: I know this is an error that's commonly asked about, but most of the time, the issue is in an INSERT statement. I couldn't find a question on this website where this error happened during an UPDATE.)
I have a table in MySQL (InnoDB / v. 5.7.19) called RESULTS which has, among others, two columns called TYPE and STATUS. Both are of type ENUM, with PASS, FAIL and IGNORE being the supported values in both. I'm trying to run this UPDATE statement on that table, using Workbench (also tried the same directly on the DB machine, using the mysql command):
update `RESULTS` set `TYPE`='IGNORE' where `STATUS`='IGNORE';
I'm getting this error:
Error Code: 1136. Column count doesn't match value count at row 1
Changing the single quotes to double quotes didn't help. I'm able to run this query successfully:
select count(`TYPE`) from `RESULTS` where `STATUS`='IGNORE';
I'm probably making a silly mistake here, but can anyone point out what's wrong with the UPDATE statement?
As requested I am posting it as an answer.
The error basically is self-explanatory like performing an operation on set of attributes but the values provided in the query are not enough. But in your case, you are performing an update operation with all attributes and their values and still, this error appears it may be a case that there is some trigger is registered for this table probably on before/after the event, If that is the case you need to update or remove that trigger if no needed.
Hypothetically, I am going to develop a trigger that inserts a record to Table A when an insertion made to an Table A.
Therefore, I want to know how the system handles that kind of loophole or it is going to continue as a loop until the system hangs which requires restart and possibly remove the DB.
I'm trying to gather information on almost every DBMS on this issue or loophole.
I can only speak to Oracle, I know nothing of MySQL.
In Oracle, this situation is known as mutation. Oracle will not spiral into an endless loop. It will detect the condition, and raise an ORA-04091 error.
That is:
ORA-04091: table XXXX is mutating, trigger/function may not see it
The standard solution is to define a package with three functions and a package level array. The three functions are as follows:
initialize - this will only zero out the array.
save_row - this will save the id of the current row (uk or pk) into the arrray.
process_rows - this will go through the array, and actually do the trigger action for each row.
Now, define some trigger actions:
statement level BEFORE: call initialize
row level BEFORE or AFTER: call save_row
statement level AFTER: call process_rows
In this way, Oracle can avoid mutation, and your trigger will work.
More details and some sample code can be found here:
https://asktom.oracle.com/pls/asktom/ASKTOM.download_file?p_file=6551198119097816936
You can only insert a record in same table if you are using instead of trigger. In all other cases you can only modify the record being inserted.
I hope this answers your quest.
you can create trigger in mysql DBMS.
check below link for create insert trigger syntex
http://www.techonthenet.com/oracle/triggers/after_insert.php
I am copying a stored procedure from one database to another. I am currently fetching the stored procedure with:
select OBJECT_DEFINITION(OBJECT_ID(N'dbo.' + #stored_procedure_name, 'P'))
and store the returned string in the variable #stored_procedure_defn.
I then run the procedure with:
exec(#stored_procedure_defn)
However I am currently getting the error
Invalid column name 'stored_procedure_name'
What could be causing this? I have tried it with a couple different procedures and the only time they mention their name is in the create procedure [dbo].['stored_procedure_name'].
EDIT Sorry my error is elsewhere. Thanks for the help.
Sounds like the stored procedure references a column that is not present in the "new" database. Note that the table is present, but the column (stored_proceudre_name) is not.
Based on what you've posted, the similarity of the invalid column name and your memvar name appears to be just a coincidence.
Problem: I've got a table which holds certain records. After the insert has been done, I want to call an external program (php script) via MySQL's sys_* UDFs.
Now, the issue - the trigger I have passes the ID of the record to the script.
When I try to pull the data out via the script, I get 0 rows.
During my own testing, I came to a conclusion that the trigger invokes the php script and passes the parameters BEFORE the actual insert occured, thus I get no records for given ID.
I've tested this on MySQL 5.0.75 and 5.1.41 (Ubuntu OS).
I can confirm that parameters get passed to the script before actual insert happens because I've added sleep(2); to my php script and I've gotten the data correctly.
Without sleep(); statement, I'm receiving 0 records for given ID.
My question is - how to fix this problem without having to hardcode some sort of delay within the php script?
I don't have the liberty of assuming that 2 seconds (or 10 seconds) will be sufficient delay, so I want everything to flow "naturally", when one command finishes - the other gets executed.
I assumed that if the trigger is of type AFTER INSERT, everything within the body of the trigger will get executed after MySQL actually inserts the data.
Table layout:
CREATE TABLE test (
id int not null auto_increment PRIMARY KEY,
random_data varchar(255) not null
);
Trigger layout:
DELIMITER $$
CREATE TRIGGER `test_after_insert` AFTER INSERT ON `test`
FOR EACH ROW BEGIN
SET #exec_var = sys_exec(CONCAT('php /var/www/xyz/servers/dispatcher.php ', NEW.id));
END;
$$
DELIMITER ;
Disclaimer: I know the security issues when using sys_exec function, my problem is that the MySQL doesn't insert FIRST and THEN call the script with necessary parameters.
If anyone can shed some light on how to fix this or has a different approach that doesn't involve SELECT INTO OUTFILE and using FAM - I'd be very grateful. Thanks in advance.
Even if you use an AFTER trigger, the row isn't committed yet. But sys_exec() doesn't return until the php script exits, so the AFTER trigger can't complete, therefore you can't commit the INSERT either.
This is by design. After all, you may do more operations within the same transaction, or you may roll back the transaction. That's the problem with invoking external processes from a trigger: external processes can't see data within the scope of the transaction in the database.
You shouldn't do this task with a trigger. At best, you should use the trigger to set a "flag" column and then write an external process to look for rows with the flag set and then invoke that PHP script. That way only rows that have successfully been inserted AND committed will be processed.
If I understand it clearly, you insert a row in your DB. That invoke a trigger that launch an external command written in PHP. That command queries in its turn the same DB by using the id of the inserted row?
I don't think this is a problem of "delay".
The real "problem" is your initial insert and you external command connect to the same DB on two different sessions -- probably in two different transactions (depending your database engine and your transaction isolation level).
I assume, when the trigger in invoked the row insert is not yet committed to the DB. So the external command still see the DB as it was before.
BTW, if the above explanation is quite speculative -- what is more evident to me is that you should probably think about a different design than trying to made that work as it is.
I user the java.sql.Statement.excecuteUpdate method to create a table and insert some values into the database through JDBC. However, it gives me MySQL syntax exceptions for no reason. I copied and pasted the same code into command prompt. it worked.
I'm wondering why it's doing that??
Guessing
You cannot do a query like: insert ...; insert ... ; only one query per method call