MySQL Sequences

How is Sequences handled in MySQL?

Sequence in MySql is handled using primary keys. Since the primary key will always be unique it can be generated in a sequence. The column, whose value is expected to be auto incremented, can be set as AUTO_INCREMENT.

Explain the purpose of Auto_increment in MySQL. Explain with an example.

Auto_increment is used to generate unique number for every row. A column can be used with Auto_increment.
Create table employee (
Id integer AUTO_INCREMENT,
Name varchar(200),
};

INSERT INTO employee (Name) VALUES (‘tom’,’jack’);

Output:
Id         Name
1          tom
2          Jack

Explain to generate sequences without using Auto_increment.

- To generate sequences without using auto_increment, LAST_INSERT_ID() is used
- If any insert or update is performed using LAST_UPDATE)ID(expr) the next call to LAST_INSERT_ID() with no argument returns the value of expr
- MySQL treats the argument passed (expr) to this function as though it was generated as a AUTO_INCREMENT value.

Example:
UPDATE table_name SET column_name LAST_INSERT_ID(column_name+1);
SELECT LAST_INSERT_ID();

Explain the issues working with Auto_increment in MySQL.

If the maximum value of the table on which auto increment is used is exceeded, auto increment stops incrementing. It does NOT result in loosing existing data but throws an error if further inserts are done.

Explain how to generate sequence in MySql.

Syntax for creating sequence:
CREATE SEQUENCE seqname [ INCREMENT increment ]
[ MINVALUE minvalue ] [ MAXVALUE maxvalue ]
[ START start ] [ CACHE cache ] [ CYCLE ]

Example:
CREATE SEQUENCE employee_id
START 200 INCREMENT 1;
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