![]() Here are the MySQL statements in Navicat for MySQL to create and populate a table with shirts and their sizes, as well as a SELECT query that fetches medium sized shirts: Specified as strings, ENUM values are automatically encoded as numbers when stored for compact storage. Many modern databases, including MySQL and SQL Server, support the ENUM data type. in order to maintain the legacy numerical values already stored in the database. For example, adding a value of Unknown to the Suit enumeration would require you to update it to: I think that you will agree that the latter is much easier to interpret as the first option requires getting at the source code and finding the numerical values that were assigned to each enumeration member.Īlthough storing strings takes more disk space, enumeration member names tend to be short, and hard drives are cheap, making the trade-off worth while to make your day-to-day job easier.Īnother problem with using numerical values is that they are difficult to update you cannot easily insert or rearrange the members without having to force the old numerical values. Now imagine that you are a database practitioner trying to decipher either of the following query results: To illustrate, imagine that we had an enum of card suits: It's usually preferable to store the actual enumeration value converted to string. Generally, it is considered bad practice to store enumerations as numerical ordinal values, as it makes debugging and support difficult. ![]() Here is an enum for representing different environment URLs (also in Java): More complex enums may also contains other types strings are the most common, but more complex objects are also supported. The most basic enums contain a set of zero-based ordinal values each represented by a constant, seen below in Java: We'll be addressing both of these issues in today's blog. Moreover, you'll want to prevent users from adding any values to the table that are not part of the permissible enum set. One of the complicating factors when storing enums in a database table is that their values may be numeric or alphabetic (i.e. Common examples include compass directions of NORTH, SOUTH, EAST, and WEST or the days of the week. As such, the variable may only hold one of the values that have been predefined for it. In the realm of Information Technology, or IT as it's more commonly known, an enum is a special data type that encapsulates a set of predefined constants. It's also interesting that I had to give column aliases in the SELECT statement to make sure the column names match those declared in the CREATE TABLE.Storing Enums In a Database by Robert Gravelle The third column f will be added automatically. It's interesting to note that you don't have to declare all three columns in the CREATE TABLE line. I tried this on MySQL 5.7.27, and it worked. Re comment from can do what you describe this way: CREATE TABLE bar (pop INT NOT NULL, name VARCHAR(100))ĪS SELECT 0 AS pop, NULL AS name, f FROM foo Here's a demonstration: CREATE TABLE foo ( f ENUM('abc', 'xyz') ) ĬREATE TABLE bar AS SELECT f AS b FROM foo įinally, I suggest that if your ENUM has many values in it (which I'm guessing is true since you're looking for a solution to avoid typing them), you should probably be using a lookup table instead of the ENUM data type. You can also use CREATE TABLE AS in creative ways to copy a type definition. You could also use the INFORMATION_SCHEMA tables to get the text of the ENUM definition, and then interpolate that into a new CREATE TABLE statement. ![]() You can mitigate the work it takes to do this by using copy & paste, or SQL scripts. ![]() You'll probably have to enter all the names again. MySQL does not support CREATE DOMAIN or CREATE TYPE as, for example, PostgreSQL does. ![]()
0 Comments
Leave a Reply. |