When I insert data into a brand new table, it will assign a new id via AUTO_INCREMENT. So the first time I perform an insert I get an id of 1. However, if I delete the row and insert new data, the table acts as if there is still a preceding row (the new row will have an id of 2). This behavior concerns me because I feel like the data is still persisting somewhere. Any ideas of what it could be?
Your data is not persisting. MySql maintains a separate table about your table containing, among other things, the next auto-increment value for your table. You can reset this with:
ALTER TABLE tablename AUTO_INCREMENT = 1
However, be aware that if you are resetting to a value below another valid value in the table, you're asking for trouble.
you should simply use.
truncate table tablename;
Related
I am working with a existing database's table from another application. I want to query newly inserted records in a fixed interval.
Normally, in a table with AUTO INCREMENT id, I can store the last fetched id and use it in the query like WHERE id > :last_id. However, this table doesn't use AUTO INCREMENT id but use uuid as primary key. So is there any way to fetch new records only?
This DB is using MySQL. I can't change the database structure. The data size is quite huge so I don't think passing fetched uuids in query like WHERE uuid NOT IN (:fetch_uuids) will be a viable solution.
Edit:
There is created field, but unfortunately there is no warranty that the records with smaller created will be inserted first. So there is the risk of missing records using it.
The data were inserted by other application, and I only have read permission in this database.
Your question doesn't state whether there is a column containing the creation time of the record. If this exists then you could use this.
You have stated you cannot change the table structure, but are you sure you cannot add columns onto the existing structure? Your problem could be solved by adding an auto-increment 'secondary' ID and/or record creation timestamp. If you cannot modify the existing tables, could you perhaps create a new table with this additional information?
A solution to your problem may be in this answer. You may be able to either add an additional column to the existing table, or alternatively insert ids into a new table where you create an ID based on a TRIGGER from the original table
I have a table1 with an id field, type AutoIncrement. I need to copy the entire record from table1 into table2 if there is no record with the same id in table2. Then I delete the record from table1.
I need to know that if table1 gets new records, the id field will never be a number that was ever used before. Does this happen automatically, or do I need to do something to ensure this?
I tried deleting some records and adding new ones, and it really didn't use the same id, but I'm not sure that this is what always happens.
It is possible to duplicate numbers in autoincremet field quite easy, but normally applications don't work this way.
Access remembers last inserted value in autoincrement field and uses it for calculating next value. You cannot insert particular value into autoincrement field using table designer or recordset in VBA, but it's possible if you use INSERT SQL statement. So, if autoincrement field has no unique index, you can insert any value. Also if you insert value less than maximum existing number, Access will generate duplicates automatically.
So I would not recommend rely on unique autoincrement numbers without unique index.
INSERT SQL can be used for resetting numeration without dropping field/table, just run query like this in query builder or using VBA:
INSERT INTO Table1 ( id ) SELECT 1;
This is table with autoincrement field ID I just created:
it is really so, Auto-increment fields in MS Access are always incremental, even if records are deleted, database compacted, etc.
The proposed number can be reset deleting the auto-increment field, perform the copy of the table and then adding the auto-increment field again.
Auto increment never uses the same # even though it's deleted from the table.
It requires complete reset so that it will start from the base and create new #.
I have a primary index on column URL but at the same time I need to have records with URL left blank which won't be permitted by the index.
I thought of a solution which is to add a new column called ID and make it auto-increment.
So I need to get the ID created with auto-increment on INSERT so that I stick it to column URL too. How can I do this?
If you can think of a better solution please tell
thanks
It is almost certainly better to use the mysql wrapper in your scripting language of choice to acquire the last insert id, but you can SELECT LAST_INSERT_ID(); to get it with mysql itself.
The solution may depend on what other columns you have on your table. It will be hard for you to add an auto_increment column to a table that already has data. The process will be to create a new table with the new column added and add the data from the old table and then drop the old table and re-name the new one to the matching name.
I know Guid are randomly generated, Is there any way I can find out which one is latest Guid? As I have to get the latest inserted record in my table as my table has no timeContext column.
Thank you
No, you cannot get this information.
If you need information, such as when a row was inserted, then you need to add a column to your table to track that information.
If you're trying to mimic the "chained insert" style of inserts, where a row is inserted into one table, the IDENTITY() value is obtained, then used to insert into further tables, you can instead generate the Guid value before the first insert - indeed, it's one of the advantages of GUID identifiers that a whole set of related table changes can be prepared in isolation, without accessing the database at all.
A client of mine accidentally deleted about 500 records from an access table that has a primary ID field which was created as "autonumber". By turning off the autonumber column (changing back to a integer), I was able to restore the missing 500 records from a backup, but now of course the autonumber cannot be turned back on...
What are some possible solutions? The ID field is used as a link to other tables, so I can't just renumber everything without also renumbering all of the tables that reference this number (a pain in the neck, but possible).
Is there any "trick" to turning autonumber back on, using the max(id) as the starting point if data already exists in the table?
Make newTable with ID field as AutoNumber (all fields must be same as in original table - except ID). Copy all data from originalTable to newTable:
INSERT INTO newTable SELECT * FROM originalTable
Once data is filled, delete originalTable and rename newTable to originalTable.
This way all "holes" in auto-numbering are preserved and newTable has Auto-Numbering turned on.
P.S. Always try to add foreign keys to your IDs. In that case, even if some data is deleted, you will at least have consistent state.
The ideal solution, although it's now too late, wouuld've been to restore the missing 500 records into a working table. Then do an Append query into the main table. This would've included the Autonumber field.
If I could add to the answers given.
A little known fact about Access autonumber fields is that the counter on them is reset when you compact and repair the database.
I am also pretty sure that if you do an insert it WILL use the numeric that is supplied rather than the next number in the autonumber counter as long as it is > (greater than) the internal counter kept by the auto-number field (does that make sense at all?)
In other words you CAN do something like this in an brand new access table where the counter should be set to 1...
INSERT INTO myTable (myAutoNumber,myOtherField) VALUES (10000,'other data')
The other solutions mentioned here are better because they would do a better job of guaranteering the result so I mention it almost for academic reasons.
Seth
Agree, but may want to add an ORDER BY to ensure that the AutoNumber is in the correct order. Otherwise your other tables will have the wrong ID association.
INSERT INTO newTable SELECT * FROM originalTable ORDER BY ID
You will also have to explicitly name the fields instead of using *
You make a new field and make it auto-number and then delete id field and rename new field to id