MySQL + SQL · Lesson 1
Er Diagram Symbols
ER Diagram Symbols
ER diagram standard shapes use करता है। हर symbol जानना common 2-3 mark exam question है।
Symbols
| Symbol | दर्शाता है |
|---|---|
| Rectangle | Entity |
| Ellipse (oval) | Attribute |
| Diamond | Relationship |
| Double ellipse | Multivalued attribute |
| Dashed ellipse | Derived attribute |
| Underlined ellipse | Key attribute |
| Double rectangle | Weak entity |
Example
Student (rectangle) — attributes roll_no (underlined oval), name (oval), phone (double oval = multivalued)। Student, Course से "enrolls" diamond के ज़रिए जुड़ता है।
सारांश
- Rectangle=entity, ellipse=attribute, diamond=relationship।
- Special: double ellipse=multivalued, dashed=derived, underline=key, double rectangle=weak entity।