| Description | string | 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.
- A non-empty set of candidate keys.
- A preferred candidate key, which may or may not be additionally designated the primary key.
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 <column name> 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 <table name> of Tb is contained in the <subtable clause> contained in the <table definition> or <view definition> 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 <value expression> sequence implied by the <select list> "*" in the <query specification> "SELECT * FROM TA". For every row RB in the value of TB there exists exactly one row RA in the value of TA such that RA is the result of the <row subquery> "SELECT SLA FROM VALUES RRB", where RRB is some <row value constructor> whose value is RB. RA is said to be the superrow in TA of RB and RB is said to be the subrow in TB of RA. If TA is a base table, then the one-to-one correspondence between superrows and subrows is guaranteed by the requirement for a unique constraint to be specified for some supertable of TA. If TA is a view, then such one-to-one correspondence is guaranteed by the requirement for a unique constraint to be specified on the leaf generally underlying table of TA. Users shall have the UNDER privilege on a table before they can use the table in a subtable definition. A table can have more than one proper subtable. Similarly, a table can have more than one proper supertable. |