![]() ![]() If I were to insert a DogId of 9223372036854775807 (the largest possible integer), I would receive the following error upon the next insert that specifies NULL for that column: Error: database or disk is full If the column had been created without the AUTOINCREMENT keyword, then the next row would reuse the DogId of 3. If I were to delete Fluff from this table, then insert a new row (using NULL as the DogId), the new DogId would be 4. Now insert data and select it: INSERT INTO Dogs VALUES Here’s an example of creating an auto-incrementing column with the AUTOINCREMENT keyword: CREATE TABLE Dogs( The downside of using the AUTOINCREMENT keyword is that it uses extra CPU, memory, disk space, and disk I/O overhead. The INSERT will fail with an SQLITE_FULL error code. If the largest possible key has previously existed in that table, then it won’t try to use previously deleted keys. Each key will always be one more than the largest key that has ever existed in that table. This is because it doesn’t reuse previously deleted keys. One benefit of using this method is that it guarantees that all rows will be in ascending order. Use the AUTOINCREMENT KeywordĪlternatively, you can choose to explicitly set the column to auto-increment by using the AUTOINCREMENT keyword. Therefore, in such cases, you can’t rely on this column if you need to order the table in ascending or descending order, based on the order of which the rows were inserted.įortunately, if this is a problem for you, there is a solution: The AUTOINCREMENT keyword. There’s a possibility that some rows will have a higher value than rows inserted at a later date. If an unused key can’t be found, the INSERT operation fails with an SQLITE_FULL error.īasically what this means is, if you allow DELETE operations in the table, then there’s no guarantee that all rows will be in order. This typically means that it will reuse old keys that were previously deleted. If the largest value of the column is the largest possible integer (9223372036854775807), then SQLite will choose an unused key at random. ![]() If the table is empty, the value will be 1. The way it works is, the NULL is automatically converted into an integer which is one greater than the largest value of that column over all other rows in the table. In other words, AUTOINCREMENT only inserts a value if you don’t. It’s important to note that you can override the AUTOINCREMENT value by inserting your own value. Now, when I insert NULL into that column, the CatId column auto-increments: INSERT INTO Cats VALUES This is because it has been defined using INTEGER PRIMARY KEY. In this table, the CatId column is an autoincrement column. Automatically Create an Auto-Increment Columnīy default, when you define a column as INTEGER PRIMARY KEY, it will auto-increment whenever you insert NULL into that column. This article explains how to create AUTOINCREMENT columns in SQLite. This is similar to an IDENTITY column in SQL Server or an AUTO_INCREMENT column in MySQL. By auto-incrementing columns, I mean columns that increment automatically whenever new data is inserted. SQLite has an interesting way of handling auto-increment columns. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |