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https://github.com/mahabubr/sql-query


https://github.com/mahabubr/sql-query

query sql

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README 

        
## Answer Questions



1. What is PostgreSQL?



- Postgresql is a relation database management system. postgres support SQL and JSON both for query. postgres used for advanced feature and powerful database management.



2. What is the purpose of a database schema in PostgreSQL?



- schema is a model of database. the purpose of postgres is a manage table, view, functions, constraints, indexes, sequences etc. postgres support many schemas on single database. database have many schema and schema have many tables.



3. Explain the primary key and foreign key concepts in PostgreSQL.



- Primary key used for specific column is unique. Foreign key used for relation to table and link up two or more tables. primary key is contain unique and the value not null. foreign key refer another table. in one table have one primary key. but foreign key have more in a table.



4. What is the difference between the VARCHAR and CHAR data types?



- VARCHAR and CHAR both is datatype on SQL. CHAR store characters in fixed length. but VARCHER hold characters length. CHAR is a fixed memory that we are mentions. but VARCHER is dynamic memory for what you give data.



5.  Explain the purpose of the WHERE clause in a SELECT statement.



- in condition we used WHERE and we use SELECT on get all or partial data. when need to condition on SQL query we need to use WHERE and on that SELECT we are use all query. we need declared SELECT on our every query.



6. What are the LIMIT and OFFSET clauses used for?



- LIMIT and OFFSET we used for pagination and get specific data onto database. limit give us how much data we need on page. and offset give the data on column number. we can dynamically handle the LIMIT and OFFSET for manage out table data. also we can add many operations on LIMIT AND OFFSET



7. How can you perform data modification using UPDATE statements?



- First we need to specify the table name that table data i need to update. then assign to new data that is update and column. then specify the row and column for where you update on WHERE clause. also we are make many conditions on WHERE. because we need to update our data on different way.



8. What is the significance of the JOIN operation, and how does it work in PostgreSQL?



- SQL JOIN operation used for join multiple table on one. SQL have many types JOIN Method. INNER JOIN, RIGHT JOIN, LEFT JOIN, FULL JOIN, CROSS JOIN etc. that join execute the table on condition and join the two or more table.



9. Explain the GROUP BY clause and its role in aggregation operations.



- GROUP BY used for manage the data and make together the same value. in SELECT statement used GROUP BY. operationally aggregate functions to produce summary reports from the database. it summarized the date into database.



10. How can you calculate aggregate functions like COUNT, SUM, and AVG in PostgreSQL?



- the count(), sum(), avg(), max() aggregation function use in SELECT. that function need integer value as parameter. the function calculate te value and add column on table. we used this aggregation function for calculate and data.



11. What is the purpose of an index in PostgreSQL, and how does it optimize query performance?



- in database indexing is powerful method. indexing used for manage data and fast the database. mainly used indexing for find our specific data in less time. its optimized database performance.



12. Explain the concept of a PostgreSQL view and how it differs from a table.



- VIEW is a virtual table of database. when we write query and manage by temporary table insert the data on VIEW. we can whenever get the data in VIEW when we need. view is a query of one or more tables that provides another way of presenting the information.