Here are top PostgreSQL interview questions,
1. What is PostgreSQL?
PostgreSQL
is a powerful open-source object-relational database management system (ORDBMS)
known for its robustness, extensibility, and SQL compliance.
2. How do you create a new database
in PostgreSQL?
To create a
new database, you can use the following SQL command:
```sql
CREATE DATABASE database_name;
```
3. How do you connect to a
PostgreSQL database using the command-line client?
You can
connect to PostgreSQL using the command-line client `psql` with the following
command:
```
psql -U username -d database_name -h host
-p port
```
Replace `username`, `database_name`,
`host`, and `port` with the appropriate values.
4. What is the command to create a
new table in PostgreSQL?
The SQL command
to create a new table is as follows:
```sql
CREATE TABLE table_name (
column1 datatype constraints,
column2 datatype constraints,
...
);
```
5. How do you insert data into a
PostgreSQL table?
To insert
data into a table, use the `INSERT INTO` statement as follows:
```sql
INSERT INTO table_name (column1, column2,
...)
VALUES (value1, value2, ...);
```
6. What is the difference between
`CHAR` and `VARCHAR` data types in PostgreSQL?
`CHAR` is a
fixed-length string type, while `VARCHAR` is a variable-length string type in
PostgreSQL. `VARCHAR` will use only as much storage as needed, whereas `CHAR`
will always use the specified length.
7. How can you retrieve all records
from a table in PostgreSQL?
You can use
the `SELECT` statement without specifying any conditions to retrieve all
records:
```sql
SELECT * FROM table_name;
```
8. What is the purpose of the
`WHERE` clause in PostgreSQL?
The `WHERE`
clause is used to filter records in a `SELECT`, `UPDATE`, or `DELETE` statement
based on specified conditions.
9. How do you update data in a
PostgreSQL table?
To update
data in a table, use the `UPDATE` statement as follows:
```sql
UPDATE table_name
SET column1 = value1, column2 = value2,
...
WHERE condition;
```
10. How can you delete records from
a PostgreSQL table?
To delete
records from a table, use the `DELETE FROM` statement along with the `WHERE`
clause to specify the condition for deletion:
```sql
DELETE FROM table_name
WHERE condition;
```
11. What is the use of the `LIMIT`
clause in PostgreSQL?
The `LIMIT`
clause is used to restrict the number of rows returned by a `SELECT` query. It
helps in pagination or when you want to retrieve a specific number of rows.
12. How do you add a new column to
an existing PostgreSQL table?
To add a
new column to an existing table, use the `ALTER TABLE` statement:
```sql
ALTER TABLE table_name
ADD COLUMN new_column_name datatype
constraints;
```
13. How can you define a primary key
when creating a table in PostgreSQL?
You can
define a primary key using the `PRIMARY KEY` constraint within the `CREATE
TABLE` statement:
```sql
CREATE TABLE table_name (
column1 datatype PRIMARY KEY,
column2 datatype,
...
);
```
14. What is the `SERIAL` data type
used for in PostgreSQL?
The
`SERIAL` data type is an auto-incrementing integer used to automatically
generate a unique value for each new row added to the table.
15. How do you create an index in
PostgreSQL?
To create
an index on a column for faster data retrieval, use the `CREATE INDEX`
statement:
```sql
CREATE INDEX index_name ON table_name
(column_name);
```
16. Explain the concept of foreign
keys in PostgreSQL.
In
PostgreSQL, foreign keys establish a relationship between two tables, where the
column with a foreign key references the primary key of another table.
17. What is the difference between
`INNER JOIN` and `LEFT JOIN` in PostgreSQL?
`INNER
JOIN` returns only the rows that have matching values in both tables, while
`LEFT JOIN` returns all rows from the left table and the matched rows from the
right table.
18. How can you perform a backup and
restore in PostgreSQL?
To perform
a backup, you can use the `pg_dump` utility, and to restore the backup, use the
`psql` command with the SQL backup file.
19. What is the purpose of the
`HAVING` clause in PostgreSQL?
The
`HAVING` clause is used to filter the results of aggregate functions in a
`GROUP BY` query, similar to the `WHERE` clause for individual rows.
20. How do you drop a table in
PostgreSQL?
To drop a
table and remove it from the database, use the `DROP TABLE` statement:
```sql
DROP TABLE table_name;
```
Above are few top PostgreSQL interview questions. Remember to prepare and expand on these answers.
Good luck with your interview! 👍
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