Possible keys coincide with UNIQUE, thus providing a semantics for their syntactic definition in the SQL standard. Certain keys extend primary keys to include NULL columns and can uniquely identify entities whenever feasible, while primary keys may not.
Dec 31, 2015
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We investigate the notions of possible and certain keys, which are keys that hold in some or all possible worlds that can originate from an SQL table, ...
Jun 8, 2016 · We investigate the notions of possible and certain keys, which are keys that hold in some or all possible worlds that originate from an SQL table, respectively.
Dec 29, 2017 · A PRIMARY KEY (PK) can have one or more columns in it. A table can have only one PK. Every table should have a PK. A "secondary key" is any index other than ...
We investigate the notions of possible and certain keys, which are keys that hold in some or all possible worlds that can originate from an SQL table, ...
We investigate the notions of possible and certain keys, which are keys that hold in some or all possible worlds that originate from an SQL table, respectively.
We propose a possible world semantics for keys over SQL tables. Possible keys hold in some possible world, while cer- tain keys hold in all possible worlds.
Nov 20, 2017 · I need to get IDs in a table that only have instances of certain keys in a column. Example: SELECT DISTINCT(myID1) as mainID FROM table1 WHERE ...
It turns out that possible keys capture the unique constraint of SQL, while certain keys extend primary keys to include NULL columns, and can be used for ...
Nov 11, 2021 · A foreign key is a column that refers to a primary key in some other table. That's it. It can have rules, like whether or not it can be null.