Currently I need to remove some rows in my DB (MySQL) and don't matter for me if this row doesn't exist in the database. In other words, I need delete rows ignoring the errors.
I know the following command:
INSERT IGNORE INTO MyTable (field1, field2) values (value1, value2);
That insert in my database the values, regardless if it already exist or not. I already go to MySQL Reference but I didn't find a good answer to this question. Also, I see some questions in StackOverflow, like this, that don't helped me.
So, exist in MySQL a command like below?
DELETE IGNORE from MyTable where myField = myValue;
Regular delete:
DELETE from MyTable where myField = myValue;
will delete all rows matching condition myField = myValue. Situation when there are no such rows is not an error and simply nothing will be deleted.
Related
bulk update like this:
update table_name set price='x1' where sku='x1'; #updated because sku=x1 exist
update table_name set price='x2' where sku='x2'; #ignored because sku=x2 does not exist
update table_name set price='x3' where sku='x3'; #ignored because sku=x2 does not exist
...about 10000 lines...
some lines did not update anything because they do not exist, I want to know, would they make mysql slow OR just affect nothing?
If you have an index on sku, then the updates should have reasonable performance. If they are in a single transaction, then the performance should be okay.
However, you would be better off putting the new data into a table and using a join for the update.
i'm using MySQL and i want to check if a record exists and if it exists delete this record.
i try this but it 's not working for me:
SELECT 'Barcelone' AS City, EXISTS(SELECT 1 FROM mytable WHERE City = 'Barcelone') AS 'exists';
THEN
DELETE FROM mytable
WHERE City = 'Barcelone';
Thank you for your help.
The if statement is only allowed in stored procedures, stored functions, and triggers (in MySQL).
If I understand what you want, just do:
DELETE FROM mytable
WHERE City = 'Barcelone';
There is no reason to check for the existence beforehand. Just delete the row. If none exist, no problem. No errors.
I would recommend an index on mytable(city) for performance reasons. If you want to check if the row exists first, that is fine, but it is unnecessary for the delete.
If you mean MySQL is returning an error message (if that's what you mean by "not working for me"), then that's exactly the behavior we would expect.
That SQL syntax is not valid for MySQL.
If you want to delete rows from a table, issue a DELETE statement, e.g.
DELETE FROM mytable WHERE City = 'Barcelone'
If you want to know how many rows were deleted (if the statement doesn't throw an error), immediately follow the DELETE statement (in the same session) with a query:
SELECT ROW_COUNT()
Or the appropriate function in whatever client library you are using.
If the ROW_COUNT() function returns 0, then there were no rows deleted.
There's really no point (in terms of MySQL) in issuing a SELECT to find out if there are rows to be deleted; the DELETE statement itself will figure it out.
If for some reason your use case requires you to check whether there are rows be be deleted, then just run a separate SELECT:
SELECT COUNT(1) FROM mytable WHERE City = 'Barcelone'
I want to insert into a table where user id = to something
And change o to 1 which means user is online
Tried this
mysql_query("INSERT INTO `20s` VALUES('','','','','','','',1) WHERE `uid`='$user_id ");
But that doesn't get me anywhere. What's the right syntax?
Also what's the best way to keep a record of online friends in the database?
TIP:it's better to use update here
Correct syntax for insert query is:
INSERT INTO table_name
VALUES (value1, value2, value3,...)
but you need here is update query, so you may update already existing row:
UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value
You only need to change one column bit that show online so dont change other columns:
UPDATE `tableName` SET `columnForOnline`=1 WHERE user_id=online_user_id
There is no WHERE clause in INSERT statements (see MySQL documentation).
If you want to update a value in an existing row, use UPDATE:
UPDATE `20s` SET `online`=1 WHERE user_id=your_user_id
mysql_ functions are deprecated, use PDO or mysqli_ instead!
MySQL also supports REPLACE INTO, which follows the same syntax as INSERT. Be careful though, columns that you do not supply will be set to their defaults.
In your case:
REPLACE INTO `20s` VALUES('','','','','','','',1) WHERE `uid`= '$user_id'
(Plus, you are missing a closing quote ' at the end of your query)
Use update query instead of insert
UPDATE `tableName` SET `columnForOnline`=1 WHERE user_id=online_user_id
UPDATE items SET name = 'haha' WHERE id = '12'
I'm curious if update also inserts the values if the where condition fails. I've read on w3schools that update only updates existing data on the database but on my script it's automatically inserting rows with the data. I am wondering if it might be a bug in the script or that's just how UPDATE works on mysql.
No. If, in your example, there's no entry with id = 12 in the database, the query will return "no rows affected". An update will never create a new entry in MySQL.
EDIT: although update won't create a new entry, it may include default/automatic values set up in your database schema (current timestamp, for instance).
NO. Update does not insert a value if the value doesn't exist in table. Please check if the script checks if the status of the update and makes another call to DB to insert the data.
Your SQL should do the following -
Update all records in the items table that have an id of 12 by setting their name to 'haha'
Update won't insert records if they don't exist, it will only update existing records in the table.
Short answer: No.
Long Answer: If your column doesn't exist you will get an error. If your where condition column doesn't exist you get error too. If your where condition value doesn't exist, it do nothing.
I use a temp table to review the data update conditions, you can refer
UPDATE table1
SET
column1 = 'things'
WHERE
IDcolumn = 'id' AND
(NOT EXISTS (SELECT * FROM (SELECT * FROM table1) AS temp WHERE temp.column1 = N'things'))
I need to write an SQL query for MySQL so that a row is updated if it exists, but inserted if it does not.
i.e.
If row exists...
UPDATE Table1 SET (...) WHERE Column1='SomeValue'
If it does not exist...
INSERT INTO Table1 VALUES (...)
Can this be done in one query?
i believe you need to reverse your logic in order for it to work:
insert into a table - if it exists (same key) then update it.
this can be achieved by the ON DUPLICATE statement like so:
INSERT INTO Table1 VALUES(...)
ON DUPLICATE KEY UPDATE column=column+1
check the manual here
Use the INSERT... ON DUPLICATE KEY UPDATE syntax.
See the manual
(For searching purposes, btw, this is usually referred to as an "upsert")