(SQL Example for Citizen Data Scientist & Business Analyst)
SQL | ALTER (ADD, DROP, MODIFY)
ALTER TABLE is used to add, delete/drop or modify columns in the existing table. It is also used to add and drop various constraints on the existing table.
ALTER TABLE – ADD
ADD is used to add columns into the existing table. Sometimes we may require to add additional information, in that case we do not require to create the whole database again, ADD comes to our rescue.
Syntax:
ALTER TABLE table_name ADD (Columnname_1 datatype, Columnname_2 datatype, … Columnname_n datatype);
ALTER TABLE – DROP
Syntax:
ALTER TABLE table_name DROP COLUMN column_name;
ALTER TABLE-MODIFY
It is used to modify the existing columns in a table. Multiple columns can also be modified at once.
*Syntax may vary slightly in different databases.
Syntax(Oracle,MySQL,MariaDB):
ALTER TABLE table_name MODIFY column_name column_type;
Syntax(SQL Server):
ALTER TABLE table_name ALTER COLUMN column_name column_type;
Queries
Sample Table:
Student
ROLL_NO | NAME |
1 | Ram |
2 | Abhi |
3 | Rahul |
4 | Tanu |
QUERY:
- To ADD 2 columns AGE and COURSE to table Student.
ALTER TABLE Student ADD (AGE number(3),COURSE varchar(40));
OUTPUT:
ROLL_NO | NAME | AGE | COURSE |
1 | Ram | ||
2 | Abhi | ||
3 | Rahul | ||
4 | Tanu |
- MODIFY column COURSE in table Student
ALTER TABLE Student MODIFY COURSE varchar(20);
After running the above query maximum size of Course Column is reduced to 20 from 40.
- DROP column COURSE in table Student.
ALTER TABLE Student DROP COLUMN COURSE;
OUTPUT:
ROLL_NO | NAME | AGE |
1 | Ram | |
2 | Abhi | |
3 | Rahul | |
4 | Tanu |
Learn to Code SQL Example – SQL | ALTER (ADD, DROP, MODIFY)
Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause. The information presented here could also be found in public knowledge domains.
Learn by Coding: v-Tutorials on Applied Machine Learning and Data Science for Beginners
Latest end-to-end Learn by Coding Projects (Jupyter Notebooks) in Python and R:
All Notebooks in One Bundle: Data Science Recipes and Examples in Python & R.
End-to-End Python Machine Learning Recipes & Examples.
End-to-End R Machine Learning Recipes & Examples.
Applied Statistics with R for Beginners and Business Professionals
Data Science and Machine Learning Projects in Python: Tabular Data Analytics
Data Science and Machine Learning Projects in R: Tabular Data Analytics
Python Machine Learning & Data Science Recipes: Learn by Coding
R Machine Learning & Data Science Recipes: Learn by Coding
Comparing Different Machine Learning Algorithms in Python for Classification (FREE)
There are 2000+ End-to-End Python & R Notebooks are available to build Professional Portfolio as a Data Scientist and/or Machine Learning Specialist. All Notebooks are only $29.95. We would like to request you to have a look at the website for FREE the end-to-end notebooks, and then decide whether you would like to purchase or not.