Can a trigger be temporary ignored in MySQL? - mysql

Question

Say table B has a BEFORE DELETE trigger. However, in some cases, I hope the trigger is disabled when I try to delete something from B, is that possible?

Answer 1

insert a conditional verification (if) inside your trigger to check whether the conditions which will do the actions will be executed or not
e.g:
create trigger ai_eav after insert on eav
for each row begin
set #id=new.entity;
set #attribute=new.attribute;
set #value=new.value;
if n > m then
update pivot set
Author=(select if(#attribute='Author',#value,Author)),
Title=(select if(#attribute='Title',#value,Title)),
Publisher=(select if(#attribute='Publisher',#value,Publisher))
where id=#id;
end if
end
you can find the syntax of mysql if statements here:
http://dev.mysql.com/doc/refman/5.0/en/if.html
this solution is probably much more performatic than deleting and recreating the trigger

Answer 2

For v5.*:
http://www.ehow.com/how_10027479_disable-triggers-mysql.html
Just drop and re-create the trigger.
For v7.0:
http://dev.mysql.com/worklog/task/?id=2825
ALTER TRIGGER ... ENABLE | DISABLE
Implementation in C:
#include <my_global.h>
#include <mysql.h>
#include <string.h>
#define TRIGGER_NAME "testtrigger"
int delete_without_trigger(MYSQL *conn,char *sql) {
if (mysql_query(conn, "SHOW CREATE TRIGGER " TRIGGER_NAME)) {
fprintf(stderr, "%s\n", mysql_error(conn));
return -1;
}
MYSQL_RES *res=mysql_use_result(conn);
MYSQL_ROW row= mysql_fetch_row(res);
char *trigger=strdup(row[2]);
//printf("TRIGGER==============\n%s\n===========\n",trigger);
mysql_free_result(res);
if (mysql_query(conn, "DROP TRIGGER " TRIGGER_NAME)) {
fprintf(stderr, "%s\n", mysql_error(conn));
return -2;
}
if (mysql_query(conn, sql)) {
fprintf(stderr, "%s\n", mysql_error(conn));
return -3;
}
if (mysql_query(conn, trigger)) {
fprintf(stderr, "%s\n", mysql_error(conn));
return -4;
}
free(trigger);
return 0;
}//delete_without_trigger
Testing:
int i;
for(i=99;--i>0;) {
printf("%d\n",i);
if(delete_without_trigger(conn,"DELETE FROM syslog WHERE txt='test'")) {
fprintf(stderr, "handling ERROR\n");
exit(1);
}
}