Column (database)

In the context of a relational database, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed. When a column allows data values of a single type, it does not essentially mean it only has simple text values. Other databases go beyond and let the data be stored as a file on Operating System whereas the column data only covers a pointer or a link to the actual file. Also, databases mostly let columns to have more complex data for example whole documents, images or even video clips.

In relational database terminology, column's equivalent is called attribute.

For example, a table that represents companies might have the following columns:

Each row would provide a data value for each column and would then be understood as a single structured data value, in this case representing a company. More formally, each row can be interpreted as a relvar, composed of a set of tuples, with each tuple consisting of the two items: the name of the relevant column and the value this row provides for that column.

Examples of database: PostgreSQL, MySQL, SQL Server, Access, Oracle, Sybase, DB2.

Coding involved: SQL [Structured Query Language]

See more at SQL.

The word 'field' is normally used interchangeably with 'column'. However, database perfectionists tends to favor to use the word 'field' to signify a specific value or single item of a column. Therefore, a field is joint of a row and column.

Relational databases mainly use row-based data storage, but column-based storage is more useful for many business applications. Column database has faster access which columns can read throughout the range process of a query. Any of the columns are known to serve as an index. Row-based application desires to progress an only record at one time and normally need to access a complete record or two. Column database has better compression as the data storage permits highly effective compression since the majority of the columns cover only few distinct values compared to number of rows. Furthermore, in a column store, data is already vertically divided. This results that operations on different columns can certainly be processed in parallel. If the multiple needs to be search or aggregated, each of these operations can be assigned to a different processor core. Overall, row based database in a row needs to check read though the obligation is to access data from a few columns. Therefore, these requests on a large amount of data take a lot of time whereas in column database tables, this information is kept physically next to each other, knowingly increasing the speed of certain data queries.

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