KwickClips Databases and SQL · 43 sec · free
How do you stop two students sharing a roll number?
Short answer. Make roll the PRIMARY KEY.
What does DEFAULT do?
It supplies a value when none is given.
Remember
| PRIMARY KEY: unique, not empty |
| NOT NULL: must have a value |
| UNIQUE: no repeats |
| DEFAULT: ready value |
How do you stop two students sharing one roll number? Primary key blocks repeats and blanks. Not null needs a value. Unique blocks repeats. Primary key, unique and filled. Not null, filled. Unique, no repeats. Default, a ready value.
This clip is from the full lesson: SQL Data Definition: CREATE DATABASE, CREATE TABLE, ALTER and DROP — 6 minutes, with the tables, the quick answers and the whole lesson in text.
Useful for: CBSE Class 10 Information Technology (402), CBSE Class 10 Information Technology (402), CBSE Class 12 Computer Science (083), CBSE Class 11 Informatics Practices (065)
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