0 0 votes Notice that we can always map 1:1 or l:N relationships in a manner similar M:N to relationships by using the cross-reference (relationship relation) approach, as we discussed earlier. This alternative is particularly useful when few relationship instances exist, in order to avoid null values in foreign keys. In this case, the primary key of the relationship relation will be only one of the foreign keys that reference the participating entity relations. For a 1:N relationship, the primary key of the relationship relation will be the foreign key that references the entity relation on the N-side. For a 1:1 relationship, either foreign key can be used as the primary key of the relationship relation as long as no null entries are present in that relation In new table created for 1:1 or 1:N , does it include entries for all the entities or only those who are participating in relationship TO AVOID NULLS ex: Table 1 or table how will it be ? Databases database-normalization er-diagram databases + – jatin khachane 1 1.2k views answer comment Share Follow Print See all 5 Comments 5 5 Comments reply Show 2 previous comments Shaik Masthan commented Oct 24, 2018 reply Follow flag ok, now i understood... just think if it includes null..... what is the key of that relationship table ? then key leads to NULL right? ∴ it just includes which are mapped only 0 0 replyShare jatin khachane 1 commented Oct 24, 2018 reply Follow flag Ok thats y we maintain separte table for 1:1 and 1:M if participating entites are very less...so that less record to maintain in relationship table.. 0 0 replyShare Shaik Masthan commented Oct 24, 2018 reply Follow flag it's depend upon your requirement someone requirement is " Minimum no.of tables. " where someone requirement is " Minimum space wasted. " 0 0 replyShare Please log in or register to add a comment.
