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An index may be declared as UNIQUE, which creates an implicit constraint on the underlying table. Database systems usually implicitly create an index on a set of columns declared PRIMARY KEY, and some are capable of using an already-existing index to police this constraint.
The create command is used to establish a new database, table, index, or stored procedure. The CREATE statement in SQL creates a component in a relational database management system (RDBMS). In the SQL 1992 specification, the types of components that can be created are schemas, tables , views , domains, character sets , collations ...
Tables are a common way of displaying data. This tutorial provides a guide to making new tables and editing existing ones. For guidelines on when and how to use tables, see the Manual of Style. The easiest way to insert a new table is to use the editing toolbar that appears when you edit a page (see image above).
{| |+ caption table code goes here |} To start a new table row, type a vertical bar and a hyphen on its own line: "|-". The codes for the cells in that row start on the next line. {| |+ The table's caption |-row code goes here |-next row code goes here |} Type the codes for each table cell in the next row, starting with a bar:
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 foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
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The two most commonly used classes are "wikitable" and "wikitable sortable"; the latter allows the reader to sort the table by clicking on the header cell of any column. |+ caption Required for accessibility purposes on data tables, and placed only between the table start and the first table row. ! header cell Optional.