I set the column Id to the primary key and set it to increment but its starting at 3 for some reason. I will post a picture below:
Sql table not incrementing correctly
You can use the ALTER TABLE statement to reset the auto-increment counter, but I would urge you not to be concerned about it. The value of a primary key is supposed to be "meaningless and unique." Even across time. It doesn't matter if it started counting with 3.
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In MySQL, I understand below
AUTO_INCREMENT: used to make INT value to increase automatically every time a user creates a row.
PRIMARY KEY: used to make value unique in that table.
However, I oftentimes see them used together when defining id.
I don't understand the point of using AUTO_INCREMENT with PRIMARY KEY since AUTO_INCREMENT itself would make id unique.
Is there any reason they are used together when creating id?
The primary key has three properties:
It is unique.
It is non-null.
There is only one per table.
Defining the key as a primary key means that it should also be used for foreign key references.
In addition, MySQL clusters the data by the primary key. So the declaration instructs new rows to go at the "end" of the table -- meaning adjacent to the most recent inserts on the data pages.
In addition, duplicate values for the auto-incremented id could be created in various ways. One way is that the increment counter can be reset, causing duplicates. MySQL should be pretty thread-safe on duplicates for concurrent updates, but bugs have been reported. As a primary key, no duplicates will be allowed into the table.
You understand it correctly, but they are doing different things.
PRIMARY KEY with AUTO_INCREMENT means we want this column isn't duplicate on the value and it will be auto increase if we didn't set the value.
but how about we only set AUTO_INCREMENT it only means it will be auto increase if we didn't set the value. but didn't make sure the value is unique.
AUTO_INCREMENT doesn't make the column uniqe. It only "automatically" fills a value when creating a row, if missing. But you can later update the values, or also create a row by explicitly providing the value.
PRIMARY KEY denies any modification sql statement that would cause 2 different entries storing equal values. So it guarantees you, that your DB is in a correct state.
We have mysql database with auto increment column(id) as primary key for all tables and which is referred in another table as foreign key. We have planned to use index for some of the columns in order to increase the accessing time of the table.
Is it necessary to create index for auto increment column(id) which is referred in another table as foreign key, or by default mysql using index mechanism internally for the column that is referred as foreign key. In any case, If we use index on foreign key, whether it will faster the accessing time ?
Thanks in advance.....
The primary key is used as a unique index, therefor you do not need to add an extra one.
If you want to be sure, you can always add the keywords EXPLAIN in front of one of your query to show the execution plan. It will display "use index" in the last column.
I need to store a build number which will start with zero and autoincrement if nothing is provided.
One solution would be to make it only a primary key and not autoincrement. However,I want it to be primary key auto increment and start with zero. Is this possible?
Per the docs, you could try this:
ALTER TABLE tbl AUTO_INCREMENT = 0;
If that doesn't work then I can't imagine what would. Personally, though, I would maintain build numbers externally instead of using auto_increment, if only because auto_increment will re-use values if you remove the row(s) with the largest keys.
Right now I have my ID field as the primary key in MySQL and have AUTO_INCREMENT on. What I want to know is how to make the ID represent the number of that row in the table rather than giving it a number when it's inserted, then sticking with that number? Because when I delete something, then that number isn't used. I want them all to be unique based on row count.
Always have a primary key. Either a basic auto increment int or a composite key of multiple fields. It helps your DB do it's job and comes in handy when you want to have relationships. Add a field called RowIndex and renumber it when you delete anything.
When you create a table don't add the AUTO_INCREMENT key word
For existing table, use
ALTER TABLE <Table_Name> MODIFY COLUMN <Column_Name> INTEGER;
to remove the AUTO_INCREMENT and the Primary key will be kept.
It is my understanding that when I make a table without a primary key that MySQL creates a sort of underlying primary key that it uses internally.
I am working with a table that does not have a primary key, but it would be very useful for my application if I could somehow access this value, assuming it does in fact exist and is retrievable.
So, I am wanting to know if I am correct in believing that such a value exists somewhere and also if it is possible to get that value.
Edit: just to make it clear, it would be very useful for my application for this table to have an incrementing int attribute. Unfortunately, it was not implemented that way. So, I am sort of grasping at straws to find a solution. What I am trying to do is select every nth row in the table (n changes). So, as you can see if there was this key, this would be very simple.
If a table has no primary key then there's no way of specifying a specific row within it because there is no way to uniquely identify an item. Even if you use a query that specifies a specific value for every column that still wouldn't be certain to only return a single row as without a primary key there's nothing to prevent duplicate rows.
However, a primary key is simply a unique index. If a table has a unique index on one or more of its columns and those columns don't accept NULLs then this is the primary key for the table in all but name.
If you table has no unique columns then you've got nothing to go on. You'll have to either make one column or combination of columns (for a composite key) unique, or add a column that serves as the primary key for the table. Fortunately it's relatively easy to add columns to a MySQL table, just add a primary key autoincrement column to the existing table.