With the query below, I am trying to overwrite the 10th field in a MySQL table called "login" with the value NEW_VALUE. It's not working. Is the code below the correct method for overwriting existing data in a MySQL table?
Thanks in advance,
John
INSERT INTO login VALUES (NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, 'NEW_VALUE', NULL, NULL, NULL)
Just as an addition if anyone is still looking for an actual overwrite and not just an update. If you want to OVERWRITE always, (not update, just overwrite) you can use REPLACE instead of INSERT.
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 13.2.5, “INSERT Syntax”
http://dev.mysql.com/doc/refman/5.5/en/replace.html
No your code is not correct. You are adding a new row to your table not updating existing values. To update existing values, you want to use an update statement:
Upate a specific record
mysql_query("Update login SET nameOfYourColumn = '$cleanURL' WHERE primaryKey = idOfRowToUpdate")
To update the entire table
mysql_query("Update login SET nameOfYourColumn = '$cleanURL'")
If I've understood your question then the answer is "no". This isn't a mysql specific issue either, it's a generic SQL question. I'd strongly recommend going through an SQL tutorial, the best one I know if is here:
http://philip.greenspun.com/sql/
To answer your question, you should be able to do:
mysql_query("UPDATE login SET foo = '$cleanurl'");
where "foo" is the name of the tenth field.
A few other comments though:
Firstly, don't rely on the position of your fields, always explicitly list the field names. For example, it's better to go
INSERT INTO login (id, name) VALUES (1, 'Fred')
instead of
INSERT INTO login VALUES (1, 'Fred')
Point 2: You have directly embedded the value of $cleanurl into your query. Of course, you have to learn one thing at a time but be aware that this is very dangerous. If $cleanurl contains something like "'); DROP TABLE login;" then you might be in trouble. This is called SQL injection and is the source of constant security problems. Without going into too much detail, you should learn how to use prepared statements.
Point 3: PHP comes with a library called PDO which supports prepared statements. It also provides a common API for interacting with your database so if you find that you need to move from Mysql to another DBMS, PDO will abstract away most of the differences. By using the mysql_query function you lock yourself into using mysql.
You don't have to address all of these issues simultaneously but don't forget about them either, once you get familiar with PHP and SQL come back to the points about PDO and prepared statements.
First off: INSERT adds a new record to a table, UPDATE updates (overwrites) one or more existing records.
Second: UPDATE needs to know the name of the column to update, and which rows to update
UPDATE <tableName>
SET <columnName> = '$cleanurl'
WHERE <some condition to identify which record should be updated>
Thirdly: it's probably worth your while reading a few basic tutorials on MySQL/SQL
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'm trying to generate unique id using php for a table ex: 2013-10-24-01 (yyyy-mm-dd-last_index_plus_1).
The problem is, if there are two session simultaneous open the php
which is access a same table, the generate unique id will be same on them.
I come up with idea that determined the number of session accessing that table
and then plus the last_index by that number,
but i don't know how to accomplished it with mysql.
Is it possible or not?
Thanks
As noted in the comment I am not sure why you want PHP to actually do this, and why the auto_increment is not good enough, but if you need a unique ID you can do the following:
Make sure to add a unique key on the column you are inserting into - if something goes wrong your database will make sure you won't get the two identical keys. In theory you could try until the query succeeds from PHP
You can use the "select for update" (http://dev.mysql.com/doc/refman/5.0/en/innodb-locking-reads.html) when selecting the last known sequence to make sure that another process will not try to read before you have inserted it.
The above is possible to do in mysql using a trigger, as you did not provide any structure, the below is just an example of how it could look. It uses a sequence-table for selecting the last id, and the mysql date_format function to format the inserted date.
delimiter |
create trigger `trigger_name`
before insert on `table_name`
for each row begin
set new.last_id = concat(date_format(now(), '%y-%m-%d'), '-', (select max(id) from `sequence_table` for update));
end|
delimiter ;
I'm looking for a standard SQL "UPSERT" statement. A one call for insert and update if exists.
I'm looking for a working, efficient and cross platform call.
I've seen MERGE, UPSERT, REPLACE, INSERT .. ON DUPLICATE UPDATE but no statement meets the needs.
BTW I use MYSQL and HSQLDB for unitests. I understand that HSQLDB is limited and may not cover what I need, but I couldn't find a standard way even without it.
A statement that only MYSQL and HSQLDB will also be enough for now.
I've been looking around for a while and couldn't get an answer.
My table:
CREATE TABLE MY_TABLE (
MY_KEY varchar(50) NOT NULL ,
MY_VALUE varchar(50) DEFAULT NULL,
TIME_STAMP bigint NOT NULL,
PRIMARY KEY (MY_KEY)
);
Any idea?
The only solution that is supported by both MySQL and HSQLDB is to query the rows you intend to replace, and conditionally either INSERT or UPDATE. This means you have to write more application code to compensate for the differences between RDBMS implementations.
START TRANSACTION.
SELECT ... FOR UPDATE.
If the SELECT finds rows, then UPDATE.
Else, INSERT.
COMMIT.
MySQL doesn't support the ANSI SQL MERGE statement. It supports REPLACE and INSERT...ON DUPLICATE KEY UPDATE. See my answer to "INSERT IGNORE" vs "INSERT ... ON DUPLICATE KEY UPDATE" for more on that.
Re comments: Yes, another approach is to just try the INSERT and see if it succeeds. Otherwise, do an UPDATE. If you attempt the INSERT and it hits a duplicate key, it'll generate an error, which turns into an exception in some client interfaces. The disadvantage of doing this in MySQL is that it generates a new auto-increment ID even if the INSERT fails. So you end up with gaps. I know gaps in auto-increment sequence are not ordinarily something to worry about, but I helped a customer last year who had gaps of 1000-1500 in between successful inserts because of this effect, and the result was that they exhausted the range of an INT in their primary key.
As #baraky says, one could instead attempt the UPDATE first, and if that affects zero rows, then do the INSERT instead. My comment on this strategy is that UPDATEing zero rows is not an exception -- you'll have to check for "number of rows affected" after the UPDATE to know whether it "succeeded" or not.
But querying the number of rows affected returns you to the original problem: you have to use different queries in MySQL versus HSQLDB.
HSQLDB:
CALL DIAGNOSTICS(ROW_COUNT);
MySQL:
SELECT ROW_COUNT();
The syntax for doing an upsert in a single command varies by RDBMS.
MySQLINSERT…ON DUPLICATE KEY UPDATE
HSQLDBMERGE
PostgresINSERT…ON CONFLICT…
See Wikipedia for more.
If you want a cross platform solution, then you'll need to use multiple commands. First check for the existing row, then conditionally insert or update as appropriate.
I have a MySQL DB which is using strict mode so I need to fill all NOT NULL values when I insert a row. The API Im creating is using just DUPLICATE KEY UPDATE functionality to do both inserts/updates.
The client application complains if any NOT NULL attributes are inserted which is expected.
Basic example (id is primary key and theare are two fields that are NOT NULL aaa and xxx)
INSERT INTO tablename (aaa, xxx, id ) VALUES ( "value", "value", 1)
ON DUPLICATE KEY UPDATE aaa=VALUES(aaa), xxx=VALUES(xxx)
All good so far. Once it is inserted, the system would allow doing updates. Nevertheless, I get the following error when updating only one of the fields.
INSERT INTO tablename (aaa, id ) VALUES ( "newValue", 1)
ON DUPLICATE KEY UPDATE aaa=VALUES(aaa)
java.sql.SQLException: Field 'xxx' doesn't have a default value
This Exception is a lie as the row is already inserted and xxx attribute has "value" as value. I would expect the following sentence to be equivalent to:
UPDATE tablename SET aaa="newValue" WHERE id=1
I would be glad if someone can shed some light about this issue.
Edit:
I can use the SQL query in PhpMyAdmin successfully to update just one field so I am afraid that this is not a SQL problem but a driver problem with JDBC. That may not have solution then.
#Marc B: Your insight is probably true and would indicate what I just described. That would mean that there is a bug in JDBC as it should not do that check when the insert is of ON DUPLICATE type as there may be a default value for the row after all. Can't provide real table data but I believe that all explained above is quite clear.
#ruakh: It does not fail to insert, neither I am expecting delayed validation. One requirement I have is to have both insert/updates done using the same query as the servlet does not know if the row exists or not. The JAVA API service only fails to update a row that has NOT NULL fields which were already filled when the insert was done. The exception is a lie because the field DOES have a default value as it was inserted before the update.
This is a typical case of DRY / SRP fail; in an attempt to not duplicate code you've created a function that violates the single responsibility principle.
The semantics of an INSERT statement is that you expect no conflicting rows; the ON DUPLICATE KEY UPDATE option is merely there to avoid handling the conflict inside your code, requiring another separate query. This is quite different from an UPDATE statement, where you would expect at least one matching row to be present.
Imagine that MySQL would only check the columns when an INSERT doesn't conflict and for some reason a row was just removed from the database and your code that expects to perform an update has to deal with an exception it doesn't expect. Given the difference in statement behaviour it's good practice to separate your insert and update logic.
Theory aside, MySQL puts together an execution plan when a query is run; in the case of an INSERT statement it has to assume that it might succeed when attempted, because that's the most optimal strategy. It prevents having to check indices etc. only to find out later that a column is missing.
This is per design and not a bug in JDBC.
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