![]() ![]() If you pass a value to LAST_INSERT_ID, it is returned by the function, but the same value is returned by the next call to LAST_INSERT_ID without a parameter. LAST_INSERT_ID is typically used to get the latest value inserted into a AUTO_INCREMENT column, but it also has another feature. Instead of using a session or local variable, you can get the same functionality using LAST_INSERT_ID function. SELECT this UPDATE statement is executed in a stored procedure, you can declare a local variable and use it after the UPDATE statement (you do not need to execute SELECT Function If UPDATE is executed as a standalone statement (not within a stored procedure), is a session variable. This statement selects the current value of the counter and increments it in a single statement: ![]() You would need two separate SQL statements: a SELECT and an UPDATE. Using transactions to increment counters is reliable but not perfect solution since locks can decrease the overall performance.įortunately, there is another option that does not require using transactions, and can select and update the counter with a single access to the table: The operation you describe, returning a resultset from a SELECT and performing an UPDATE cannot be performed in a single SQL statement in MySQL. Now if a transaction executes SELECT FOR UPDATE, all other concurrent transactions will be blocked on execution of their SELECT FOR UPDATE until the first transaction issues a COMMIT, or lock time-out expires. Let's get the current value SELECT value FROM counters WHERE id = 1 FOR UPDATE To resolve this issue we can start a transaction and you SELECT FOR UPDATE in MySQL: The problem with this query is that concurrent sessions can execute SELECT at the same time and get the same current value. Increment the counter UPDATE counters SET value = value + 1 WHERE id = 1 Let's get the current value SELECT value FROM counters WHERE id = 1 In terms of MySQL, it is not necessary to run a SELECT before running an UPDATE, it's possible to run just an UPDATE. ![]() Initialize the first counter with start value 10 INSERT INTO counters VALUES (1, 10 ) The operation you describe, returning a resultset from a SELECT and performing an UPDATE cannot be performed in a single SQL statement in MySQL. Value INT - current value of the counter ) Id INT NOT NULL UNIQUE, - multiple counters can be stored in this table, this is its id Why not to use SELECT statement to get the current value and then UPDATE to update the counter: This current value will be used as an ID for some operation, so concurrent sessions must not get the same value. columnN WHERE condition In this case the parameters supplied are used in the select query that provides replacement values in the outer update statement. Now on the update.php, you can do something like this.Assume you a have a counter, and before you increment it, you need to get its current value. while ($row=mysql_fetch_assoc($query)) // this must be the end of your while loop I hope you understand what I am trying to say. Updating a value in MySQL is a simple task that can be accomplished using the UPDATE statement together with the SET clause. it is safer to just stay away from them, rather than getting at them at close range. I know the $fetch is not an actual reserved words, but FETCH does. ![]() There are many PHP reserved words that we should avoid. this variable name can and may have a naming colision issues later on. otherwise your site will be highly vulnerable.ĭon't use fetch as your variable name. !WARNING! Be careful when adding form inputted data in your database, make sure to sanitize these data. $query = mysql_query("SELECT * FROM REVIEW WHERE title = '". Your query can be modified to something like this. ĭid you try adding a name atribute in your ? Like this. I am having trouble in figuring out how to populate the forms which will display the inforamtion related to the dropdown selection. This is the code I have written to populate the dropdown menu with the movie titles stored in the database which is working. The third step is to then run an update query to alter the databse. INSERT INTO table1 (title) SELECT title FROM table2 ON DUPLICATE KEY UPDATE status Used. The second step is to populate a set of forms which related to the movie that was selected from the dropdown box so the information can be edited. This will only work if you have PRIMARY KEY (title) on table1. I want to be able to update my database in order to change some dynamic content on my site which contains movie reviews.įirst Step I need to be able to select which movie review I want to update by selecting it from a dropdown menu which is dynamically populated by the database. ![]()
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