On 11-11-2017 11:13, m_brahi...@yahoo.fr [firebird-support] wrote: > I need to know please if it is allowed that a primary key has multiple > integer fields ? and only that. For example a PK that has seven integer > fields will it decrease the performance table ? I am using FB 3. Thanks
Of course you can do that. See https://www.firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-ddl-tbl.html <tconstraint> ::= [CONSTRAINT constr_name] { PRIMARY KEY (col_list) [<using_index>] | UNIQUE (col_list) [<using_index>] | FOREIGN KEY (col_list) REFERENCES other_table [(col_list)] [<using_index>] [ON DELETE {NO ACTION | CASCADE | SET DEFAULT | SET NULL}] [ON UPDATE {NO ACTION | CASCADE | SET DEFAULT | SET NULL}] | CHECK (<check_condition>) }" <col_list> ::= colname [, colname ...] In other words, a table constraint, including a primary key, can consist of multiple columns (contrary to a column constraint, which is only on a single column). Will it decrease performance? Of course it will, more columns means a larger key, which means bigger indexes, and thus a decrease in performance on insert and likely also on lookup. A key of seven integers means a key of 7 * 4 bytes = 28 bytes (+ maybe some bytes overhead, I keep forgetting implementation details like that). The decrease in performance is probably not excessive, but if the decrease in performance is acceptable or not is up to you. Mark -- Mark Rotteveel
