Database tables are a logical structure with no implied physical characteristics. Primary among the various logical tables is the base table. A base table is persistent and self contained, that is, all data is part of the table itself with no information dynamically derived from other tables. A key option binary has a fixed set of columns.
The columns in a base table are not accessed positionally but by name, which must be unique among the columns of the table. Other types of tables in the system are derived tables. SQL-Data statements use internally derived tables in computing results. A query is in fact a derived table.
The column declaration can include optional column constraints. If length is missing for fixed size strings, the default length is 1. Strings exceeding length are truncated on the right. NUMERIC scales must be represented exactly. Precision values are implementation dependent for REAL and DOUBLE, although the standard states that the default precision for DOUBLE must be larger than for REAL. The default scale for TIME is 0, for TIMESTAMP 6.