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Lossless join decomposition
Decompositions are not always lossless.
Example
XYZ
X
Y
Z
1
aaa
666
1
bbb
777
2
aaa
777
XY = project(XYZ, [X, Y])
X
Y
1
aaa
1
bbb
2
aaa
XZ = project(XYZ, [X, Z])
X
Z
1
666
1
777
2
777
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