What is the use of enums?
Enums are used when we know all possible values at compile time, such as choices on a menu, rounding modes, command line flags, etc. It is not necessary that the set of constants in an enum type stay fixed for all time. In Java (from 1.5), enums are represented using enum data type.
Why is ENUM bad MySQL?
Data isn’t being treated like data. With an ENUM we’re actually storing pieces of data in a place that was only intended to hold crucial information about the model. In short, an ENUM column violates the rules of normalization.
How are enums stored in MySQL?
The ENUM data type is stored in two locations: the set of values is stored in the table metadata; in each row, only the set index is stored, as integer, which requires one byte for enums up to 255 entries large, then two for up to 65535 entries (see MySQL reference)
What is the difference between ENUM and set in MySQL?
Difference between SET and ENUM. The difference between SET and ENUM is that SET column can contain multiple values and whereas an ENUM can hold only one of the possible values. The SET type is similar to ENUM whereas the SET type is stored as a full value rather than an index of a value as with ENUM.
Is enum good in MySQL?
ENUM is great for data that you know will fall within a static set. If you are using Mysql 5+, storage is almost always better with an ENUM type for data in a static set, as the official MySQL reference shows. Not to mention that the data is readable, and you have an extra layer of validation.
Should I use enums in database?
Enum types are more convenient for coding. For infrequent releases, or if you often have new/deleted/changed values, use a database table. For static sets of values, or if you release code all the time, use an enum.
How many columns can be used for creating index?
An index may consist of up to 16 columns. For certain data types, you can index a prefix of the column (see Section 8.3.
Can enum be null MySQL?
5 Answers. MySQL will allow the value to be NULL if you do not specify NOT NULL in the column definition. In ENUM data type, if you do not declare NOT NULL then it gives the default value NULL. However, if you declare NOT NULL then it gives the first value from the ENUM.
Is index a constraint in SQL?
Is an index a constraint? Not really, but a unique index has the same effect as a unique constraint on the same columns. So, you can think of a unique index as implementing a unique constraint.
What is ENUM in SQL?
An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation time.
Does an enum in MySQL need to be not null?
MySQL allows us to define the ENUM data type with the following three attributes – If we don’t want NULL values, it is required to use the NOT NULL property in the ENUM column. It is a synonym for DEFAULT NULL, and its index value is always NULL. By default, the ENUM data type is NULL, if the user doesn’t want to pass any value to it.
What is select in MySQL?
MySQL – Select Query. The SQL SELECT command is used to fetch data from the MySQL database. You can use this command at mysql> prompt as well as in any script like PHP.
What is enum in SQL?
ENUM is a data type in MySQL, but not in standard ANSI/ISO SQL or in any other major brand of SQL database. The MySQL manual says: “An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation time.”.
What is SELECT statement in MySQL?
MySQL Select Statement. SELECT statement is used to retrieve data. It can be combined with many sub statements to specify more criteria on data to be retrieved. For examples in this article, we are going to use `employee` table mentioned below. SQL commands for creating the table and inserting data are available here.