I had a table with unique Date_t1 date type field, but in Table description field is not mentioned as unique, now while inserting new row I need to validate if date exist or not, If already exist I should not allow to make changes on that row, neither a new row needs to be created, Any idea how to resolve this problem in efficient way,
Since you're using a UNIQUE index.. you can use this to your advantage with INSERT IGNORE
Consider the following:
INSERT IGNORE INTO your_table SET id = 100 ...
Assuming id is the UNIQUE column here... MySQL will throw an error if you try to re-insert this. But since you're using IGNORE, the error is silently thrown away.
Related
This question already has answers here:
How can I do 'insert if not exists' in MySQL?
(11 answers)
Closed 1 year ago.
I found a not so nice method for checking if there a row already exists, and if it does exists, then it doesn't add it to avoid duplicates. Am i completely crazy to rely on this method or should i go old fashioned way where i check if it exists BEFORE trying to insert row in database?
The table is VERY simple :)
-ID [PK]
-Message
-Hashed_message [UNIQUE] (stored procedure, takes message and hashes it upon insert)
Now when i try to insert a new row i would say
*`insert into .... message = xxx
Upon insertion mysql will create a hash on message automatically, but since it's an unique column, incase the hash already exists in database, it will simply throw an error, and no duplicates will exist ever... i hope.
The reason for using hashes, is simply to avoid checking duplicates by scanning every large message, instead i though a short hash would be easier to check for duplicates.
So is this method bad for avoiding duplicates?
I mean i could before insert, manually create that hash of my message and check if that hash exists and THEN insert the message, but i would hope to avoid always trying to match the stored procedure function on PHP as well.
quick note: there is a similar thread about insert and then ignoring error on duplicate, but this one is related to how it is handled when a derived column(Stored procedure) is used to accomplish this
If the hashed message has to be unique, create a key on that column with the UNIQUE constrain: so there won't be two rows with the same hash.
Then, when you insert a new row modify your query with the following:
INSERT INTO table SET message='$message', hashed_message='$hashed_message'
ON DUPLICATE KEY id=id;
This will perform an insert if the hashed_message is unique. Otherwise will not do any update.
If you want to update something in case of duplicate your query will become:
INSERT INTO table SET message='$message', hashed_message='$hashed_message'
ON DUPLICATE KEY UPDATE message='$updated_message'
just to make an example.
Note that this method won't raise any exception in case of duplicate values: you need extra logic if you need to perform actions in your frontend in case of duplicates (i.e. message shown to the user).
More details here
I have an INSERT statement with an IGNORE option, because I have a unique field in the insert statement, that is not the primary key. I am using the getGeneratedKeys() command on a PreparedStatement object to get the keys of newly generated rows. Is it possible to configure JDBC in a way so that it returns the id of the ignored row in the case of a query where the IGNORE triggers?
The answer mysql - after insert ignore get primary key seems to indicate that a multi-step workaround is required to retrieve the details of the ignored rows.
With the optional alternative of using REPLACE INTO if you can afford the additional overhead of replacing the rows rather than ignoring them.
I was once told that it is faster to just run an insert and let the insert fail than to check if a database entry exists and then inserting if it is missing.
I was also told that that most databases are heavily optimized for reading reading rather than writing, so wouldn't a quick check be faster than a slow insert?
Is this a question of the expected number of collisions? (IE it's faster to insert only if there is a low chance of the entry already existing.) Does it depend on the database type I am running? And for that matter, is it bad practice to have a method that is going to be constantly adding insert errors to my error log?
Thanks.
If the insert is going to fail because of an index violation, it will be at most marginally slower than a check that the record exists. (Both require checking whether the index contains the value.) If the insert is going to succeed, then issuing two queries is significantly slower than issuing one.
You can use INSERT IGNORE so that if the key already exist, the insert command would just be ignored, else the new row will be inserted. This way you need to issue a single query, which checks the duplicate values as well inserts new values too.
still Be careful with INSERT IGNORE as it turns EVERY error into a warning. Read this post for insert ignore
On duplicate key ignore?
I think INSERT IGNORE INTO .... can be used here, either it will insert or ignore it.
If you use the IGNORE keyword, errors that occur while executing the INSERT statement are treated as warnings instead. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted. With IGNORE, the row still is not inserted, but no error is issued.
If you want to delete the old value and insert a new value you can use REPLACE You can use REPLACE instead of INSERT to overwrite old rows.
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.
Else use the INSERT IGNORE as it will either inserts or ignores.
a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted. With IGNORE, the row still is not inserted, but no error is issued.
If your intension is to Insert if its a new record OR Update the record if it already exists then how about doing an UPSERT?
Check out - http://vadivel.blogspot.com/2011/09/upsert-insert-and-update-in-sql-server.html
Instead of checking whether the record exists or not we can try to Update it directly. If there is no matching record then ##RowCount would be 0. Based on that we can Insert it as a new record. [In SQL Server 2008 you can use MERGE concept for this]
EDIT: Please note, I know this works for MS SQL Server and I don't know about MySQL or ORACLE
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'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