A representation of the model object 'Table'.
4.14 Tables
A table is a collection of rows having one or more columns. A row is a value of a row type. Every row of the same table has the same row type. The value of the i-th field of every row in a table is the value of the i-th column of that row in the table. The row is the smallest unit of data that can be inserted into a table and deleted from a table.
The degree of a table, and the degree of each of its rows, is the number of columns of that table. The number of rows in a table is its cardinality. A table whose cardinality is 0 (zero) is said to be empty.
A table is either a base table, a derived table, or a transient table. A base table is either a persistent base table, a global temporary table, a created local temporary table, or a declared local temporary table.
A table is described by a table descriptor. A table descriptor is either a base table descriptor, a view descriptor, or a derived table descriptor (for a derived table that is not a view).
Every table descriptor includes:
- The column descriptor of each column in the table.
- The name, if any, of the structured type, if any, associated with the table.
- An indication of whether the table is insertable-into or not.
- An indication of whether the table is a referenceable table or not, and an indication of whether the selfreferencing column is a system-generated, a user-generated, or a derived self-referencing column.
- A list, possibly empty, of the names of its direct supertables.
- A list, possibly empty, of the names of its direct subtables.
A base table descriptor describes a base table. In addition to the components of every table descriptor, a base table descriptor includes:
- The name of the base table.
- An indication of whether the table is a persistent base table, a global temporary table, a created local temporary table, or a declared local temporary table.
- If the base table is a global temporary table, a created local temporary table, or a declared local temporary table, then an indication of whether ON COMMIT PRESERVE ROWS was specified or ON COMMIT DELETE ROWS was specified or implied.
- The descriptor of each table constraint specified for the table.
- A non-empty set of functional dependencies, according to the rules given in Subclause 4.18, "Functional dependencies".
- A non-empty set of candidate keys, according to the rules of Subclause 4.19, "Candidate keys".
- A preferred candidate key, which may or may not be additionally designated the primary key, according to the Rules in Subclause 4.18, "Functional dependencies".
4.14.2 Referenceable tables, subtables, and supertables
A table RT whose row type is derived from a structured type ST is called a typed table. Only a base table or a view can be a typed table. A typed table has columns corresponding, in name and declared type, to every attribute of ST and one other column REFC that is the self-referencing column of RT; let REFCN be the of REFC. The declared type of REFC is necessarily REF (ST) and the nullability characteristic of REFC is known not nullable. If RT is a base table, then the table constraint "UNIQUE (REFCN)" is implicit in the definition of RT. A typed table is called a referenceable table. A self-referencing column cannot be updated.
Its value is determined during the insertion of a row into the referenceable table. The value of a system-generated self-referencing column and a derived self-referencing column is automatically generated when the row is inserted into the referenceable table. The value of a user-generated self-referencing column is supplied as part of the candidate row to be inserted into the referenceable table.
A table Ta is a direct subtable of another table Tb if and only if the
of Tb is contained in the contained in the
or of Ta. Both Ta and Tb shall be created on a structured type and the structured type of Ta shall be a direct subtype of the structured type of Tb.
A table Ta is a subtable of a table Tb if and only if any of the following are true:
1) Ta and Tb are the same named table.
2) Ta is a direct subtable of Tb.
3) There is a table Tc such that Ta is a direct subtable of Tc and Tc is a subtable of Tb.
A table T is considered to be one of its own subtables. Subtables of T other than T itself are called its proper subtables. A table shall not have itself as a proper subtable.
A table Tb is called a supertable of a table Ta if Ta is a subtable of Tb. If Ta is a direct subtable of Tb, then Tb is called a direct supertable of Ta. A table that is not a subtable of any other table is called a maximal supertable. Let Ta be a maximal supertable and T be a subtable of Ta. The set of all subtables of Ta (which includes Ta itself) is called the subtable family of T or (equivalently) of Ta. Every subtable family has exactly one maximal supertable. A leaf table is a table that does not have any proper subtables.
Those columns of a subtable Ta of a structured type STa that correspond to the inherited attributes of STa are
called inherited columns. Those columns of Ta that correspond to the originally-defined attributes of STa are
called originally-defined columns.
Let TB be a subtable of TA. Let SLA be the sequence implied by the