Spurious Tuples in DBMS

In Database Management System (DBMS), data is represented in a tabular form through attributes and tuples i.e., columns and rows.
There are various operations (insert, delete, update, modify, etc.) that we can perform on tables. One such operation is join. When we combine two tables into one, we call it a join and it is denoted by ⨝.

Spurious Tuples :
Spurious Tuples are those rows in a table, which occur as a result of joining two tables in wrong manner. They are extra tuples (rows) which might not be required.

If relation is denoted by R, and its decomposed relations are denoted by R1, R2, R3….Rn, then, condition for not getting any Spurious Tuple is denoted by,

R1 ⨝ R2 ⨝ R3 .... ⨝ Rn = R

Whereas condition for getting Spurious Tuples is denoted by,

R ⊂ R1 ⨝ R2 ⨝ R3 .... ⨝ Rn

Example-1:
Example to check if given relation contains Spurious Tuples.
Let R be Relation, and R1 and R2 be relations which we get after decomposing R.



After performing join operation of relations R1 and R2 (R1 ⨝ R2), we get back original relation R.

The condition for no spurious tuples, R1 ⨝ R2 = R, is met. Hence, we do not get any Spurious Tuples.

Conclusion – No Spurious Tuple exists.

Example-2:
Example to check if given relation contains Spurious Tuples.
Let R be Relation, and R1 and R2 be relations which we get after decomposing R.

After performing join operation of relations R1 and R2 (R1 ⨝ R2), we do not get back original relation R.

The condition for spurious tuples, R ⊂ R1 ⨝ R2, is met. Hence, we get Spurious Tuples.

Conclusion – Spurious Tuples exist.

Note –
Rows in DBMS are called tuples. Whereas, columns in DBMS are called attributes. Spurious Tuples can be remembered as extra rows in table. The natural join leading to Spurious Tuples is called Lossy Join. The natural join not resulting in Spurious Tuples is called Lossless Join.

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