I'm trying to create a code for a single button where it will perform either of two actions where it will add to the database if the user currently don't have the record while it will update the user's record if the user has records already. I've done it like this:
if() {
mysql_query("INSERT INTO table...");
}
else {
mysql_query("UPDATE table SET...");
}
Is it possible?
Yes, what you've written will work. If you have a way to know if there already exists a row or not without making an additional query just for this bit of code, then do exactly as you wrote.
If, however, you planned to first SELECT from the table to see if a row exists, then conditionally INSERT or UPDATE, you will perform more queries than necessary.
It would be better to either:
Have a PRIMARY KEY or other constraint on the table prevent duplicate INSERTs. Then issue an INSERT ... ON DUPLICATE KEY UPDATE query. This will attempt to INSERT the row, and if it is a duplicate, automatically perform the specified UPDATE to that row instead.
Issue the UPDATE query and check mysql_affected_rows to see if it updated an existing row. If not, then issue the INSERT query to create the new row.
Which one is more appropriate depends on your application.
you can use INSERT ... ON DUPLICATE KEY UPDATE Syntax like:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=c+1;
http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
If you have properly set unique keys, you should use REPLACE so you could remove the if.
REPLACE INTO table VALUE (...);
Pay attention that this is a MySQL extension, thus not portable to other DBs.
Yes, you could try the insert then if it fails try the update.
But you could use the MYSQL sql "REPLACE" keyword, which will insert a new record if it doesn't exist or delete the existing record and insert your new one if it does.
You could also use the INSERT ... ON DUPLICATE KEY UPDATE syntax
(explained here - Link to MYSQL ref which seems to be the closest fit to your requirement.
yes it is possible
first write a query for check that record is already exist or not.
Yes it is possible , it will work
Related
I'm developing a php script in which I insert multiple data into a mysql table, but some of this data may already be inserted. I can try to insert each of the individual data and detect the #1062 error (duplicate entry), but it would be very inefficient since it can be more than 100 entries. So, is there any way to do this in one query or must I use a query for each entry to be inserted?
Thanks a lot.
You'll want to use the INSERT ... ON DUPLICATE KEY UPDATE command to accomplish this. In the "ON DUPLICATE KEY UPDATE" section, you can just do some kind of update that changes nothing. For example, "SET fieldName=fieldName", just so nothing is actually changed.
http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
I have an INSERT query which looks like:
$db->Query("INSERT INTO `surfed` (user, site) VALUES('".$data['id']."', '".$id."')");
Basically I want to insert just like the above query but if the site is already submitted by another user I don't want it to then re-submit the same $id in to the site column. But multiple users can view the same site and all users need to be in the same row as the site that they have viewed which causes the surfed table to have 10s of thousands of inserts which dramatically slows down the site.
Is there any way to maybe split up the insert in some way so that if a site is already submitted it won't then submit it again for another user. Maybe there's a way to use UPDATE so that there isn't an overload of inserts?
Thanks,
I guess the easiest way to do it would be setting up a stored procedure which executes a SELECT to check if the user-site-combination is already in the table. If not, you execute the insert statement. If that combination already exist, you're done and don't execute the insert.
Check out the manual on stored procedures
http://dev.mysql.com/doc/refman/5.1/en/create-procedure.html
You need to set a conditional statement that asks whether the id already exists then if it does update otherwise insert
If you don't need to know whether you actually inserted a line, you can use INSERT IGNORE ....
$db->Query("INSERT IGNORE INTO `surfed` (user, site) VALUES('".$data['id']."', '".$id."')");
But this assumes that you have a unique key defined for the columns.
IGNORE here will ignore the Integrity constraint violation error triggered by attempting to add the same unique key twice.
The MySQL Reference Manual on the INSERT syntax has some informations on that http://dev.mysql.com/doc/refman/5.5/en/insert.html
If a column is made unique in a database table structure, is there any need to do a check to see if a new value to be inserted already exists in the table via script? Or would it be fine just to insert values letting the DBMS filter non-new values?
When you will try to insert a duplicate value in a unique column, your insert query will fail. So it might be a good idea to make sure you are checking to see if your insert queries went well or not. Althought regardless of the situation you should always check if your insert query went through or not :)
You should always validate your data before inserting it on the database. That being said, what will happen if you try to insert a non-unique value on a unique defined column is an SQLexception.
In order to validate this before insertion, you could for example do a
select 1
from mytable_with_unique_column
where my_unique_column = myNewValue
If the query returns anything, then simply do not try to insert as that will throw an SQLException.
Verification of unique constraint is definitely an overkill.
When you put unique constraint on your column, an implicit index is created for this column. Thus, DBMS can (and will) verify your data much faster. Unfortunately, when you try to insert duplicate value into your column, you will get constraint violation exception you have to deal with (but you have to deal with such error while using script verification either).
Good luck.
You can combine the insert statement and validation select into one statement:
insert into mytable_with_unique_column (...) values (...)
where not exists
(
select 1
from mytable_with_unique_column
where my_unique_column = myNewValue
)
This will only insert a new row if there isn't already a row with the given unique value.
I have two INSERT commands, that are useless to me like that because the two sets of rows - the ones that are already in the table, and the ones I have as INSERT commands - are not disjunct. Both commands insert lots of rows, and lots of values.
Therefore I get the duplicate entry error if I want to execute those lines.
Is there any easy way to 'convert' those commands into UPDATE?
I know this sounds stupid, because why do I make INSERT commands, if I want to UPDATE. Just to make it a clear scenario: another developer gave me the script:)
Thanks in advance,
Daniel
EDIT - problem solved
First I created a table and filled it up with my INSERT commands, then I used the following REPLACE command:
REPLACE
INTO table_1
SELECT *
FROM table_2;
This can originally be found at: How can I merge two MySQL tables?
MySQL's REPLACE keyword does this. Simply replace the INSERT keyword in your queries with the word REPLACE and it should update the rows instead of inserting new ones. Please note that it will only work if you're inserting a primary key or unique key column.
You would have to rewrite them to updates by hand. If I encouter such a problem, I query for the count of certain primary key first, if none is found I insert a generic dataset and update it afterwards. By this, new data can be added and already existing data will be updated, and you don't have to differentiate between inserting new data and updating data.
For MySQL, you can use either the INSERT IGNORE or the INSERT ... ON DUPLICATE UPDATE syntaxes. See the MySQL reference manual
You can easily modify your queries to update duplicate rows, see INSERT ... ON DUPLICATE KEY syntax in MySQL
In MySQL, I'm trying to find an efficient way to perform an UPDATE if a row already exists in a table, or an INSERT if the row doesn't exist.
I've found two possible ways so far:
The obvious one: open a transaction, SELECT to find if the row exists, INSERT if it doesn't exist or UPDATE if it exists, commit transaction
first INSERT IGNORE into the table (so no error is raised if the row already exists), then UPDATE
The second method avoids the transaction.
Which one do you think is more efficient, and are there better ways (for example using a trigger)?
INSERT ... ON DUPLICATE KEY UPDATE
You could also perform an UPDATE, check the number of rows affected, if it's less than 1, then it didn't find a matching row, so perfom the INSERT.
There is another way - REPLACE.
REPLACE INTO myTable (col1) VALUES (value1)
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted. See Section 12.2.5, “INSERT Syntax”.
In mysql there's a REPLACE statement that, I believe, does more or less what you want it to do.
REPLACE INTO would be a solution, it uses the UNIQUE INDEX for replacing or inserting something.
REPLACE INTO
yourTable
SET
column = value;
Please be aware that this works differently from what you might expect, the REPLACE is quite literally. It first checks if there is a UNIQUE INDEX collision which would prevent an INSERT, it removes (DELETE) all rows which collide and then INSERTs the row you've given it.
This, for example, leads to subtle problems like Triggers not firing (because they check for an update, which never occurs) or values reverted to the defaults (because you must specify all values).
If you're doing a lot of these, it might be worth writing them to a file, and then using 'LOAD DATA INFILE ... REPLACE ...'