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National standard format is yyyy-mm-dd. [161] dd.mm.yyyy format is used in some places where it is required by EU regulations, for example for best-before dates on food [162] and on driver's licenses. d/m format is used casually, when the year is obvious from the context, and for date ranges, e.g. 28-31/8 for 28–31 August.
[4] [3] For example, a table of 128 rows with a Boolean column requires 128 bytes a row-oriented format (one byte per Boolean) but 128 bits (16 bytes) in a column-oriented format (via a bitmap). Another example is the use of run-length encoding to encode a column.
Reserved words in SQL and related products In SQL:2023 [3] In IBM Db2 13 [4] In Mimer SQL 11.0 [5] In MySQL 8.0 [6] In Oracle Database 23c [7] In PostgreSQL 16 [1] In Microsoft SQL Server 2022 [2]
MySQL provides an enumerated type ENUM with allowable values specified as strings when a table is created. The values are stored as numeric indices with the empty string stored as 0, the first string value stored as 1, the second string value stored as 2, etc. Values can be stored and retrieved as numeric indexes or string values.
Note: This example is not accessible, and should be avoided as much as possible. For example, nested tables (tables inside tables) should be separated into distinct tables when possible. Here is a more advanced example, showing some more options available for making up tables.
A key that can be used to uniquely identify a row in a table is called a primary key. Keys are commonly used to join or combine data from two or more tables. For example, an Employee table may contain a column named Location which contains a value that matches the key of a Location table. Keys are also critical in the creation of indexes, which ...
A derived table is the use of referencing an SQL subquery in a FROM clause. Essentially, the derived table is a subquery that can be selected from or joined to. The derived table functionality allows the user to reference the subquery as a table. The derived table is sometimes referred to as an inline view or a subselect.
A delimited text file is a text file used to store data, in which each line represents a single book, company, or other thing, and each line has fields separated by the delimiter. [3] Compared to the kind of flat file that uses spaces to force every field to the same width, a delimited file has the advantage of allowing field values of any length.