When to use an auto-incremented primary key and when not to?
If the primary key is ISBN, I could simply write "select count(*) from sale where isbn='143573338X'". If I used an autoincrement key, I would have to do a join to look up the isbn, and the query becomes more complex and slower, like "select count(*) from book join sale using (bookid) where isbn='143573338X'".
What is the difference between SERIAL and AUTO_INCREMENT in …
If no value is specified for the AUTO_INCREMENT column, MySQL assigned sequence numbers automatically. You can also explicitly assign NULL or 0 to the column to generate sequence numbers. MySQL doesn't automatically decrease the autoincrement value when you delete a …
Pros and Cons of autoincrement keys on "every table"
2010年1月4日 · We are having a rather long discussion in our company about whether or not to put an autoincrement key on EVERY table in our database. I can understand putting one on tables that would have a FK reference to, but I kind-of dislike putting such keys on each and every one of our tables, even though the keys would never be used.
How to set initial value and auto increment in MySQL?
When the table structure view opens, go to tab "Options" (on the lower bottom of the view), and set "Auto Increment" field to the value of the next autoincrement number. Don't forget to hit "Apply" when you are done with all changes. PhpMyAdmin:
How to set auto increment primary key in PostgreSQL?
COPY epictable TO '/tmp/etbackup.csv' DELIMITER ',' CSV HEADER; CREATE TABLE epictable2 ( mytable_key integer, moobars VARCHAR(40) not null, foobars DATE ); COPY epictable2(mytable_key, moobars, foobars) FROM '/tmp/etbackup.csv' DELIMITER ',' CSV HEADER; --and again to make the duplicates requiring an autoincrement: COPY …
SQLITE: Best practices about using AUTOINCREMENT
2018年10月8日 · Whilst without AUTOINCREMENT attempts will be made to get an unused id/rowid. AUTOINCREMENT adds a row (table if required) to sqlite_sequence that records the highest allocated id. The difference between with and without AUTOINCREMENT is that the sqlite_sequecence table is referenced, whilst without AUTOINCREMENT the isn't.
SQL Server add auto increment primary key to existing table
2017年7月14日 · This answer is a small addition to the highest voted answer and works for SQL Server. The question requested an auto increment primary key, the current answer does add the primary key, but it is not flagged as auto-increment. The script below checks for the columns, existence, and adds it with the autoincrement flag enabled.
sql server - How to autoincrement a varchar? - Stack Overflow
2011年1月15日 · Then set AUTOINCREMENT on column_2. And yes, your Primary Key can be (column_1, column_2), so you have not lost whatever meaning c0002 has for you. Never place suppliers and customers (whatever "c" and "s" means) in the same table. If you do that, you will not have a database table, you will have a flat file.
c# - PrimaryKey and AutoIncrement - Stack Overflow
2018年9月25日 · Thus AUTOINCREMENT compliments INTEGER PRIMARY KEY to impose the restriction that the unique value must always increase. It does this at some expense as it uses a table called sqlite_sequence to store the highest allocated rowid (or alias thereof).
Auto increment primary key in SQL Server Management Studio 2012
2012年6月12日 · Just a bit of correction: The IDENTITY property could be applied to any numeric data types (so it could be tinyint, smallint, int, bigint, numeric, decimal), the only constraint is that it could not represent fractional number (so it can't be float or real, neither numeric or decimal with non-zero scale) and ofc, the identity spec should be compatible with the selected data type.