PostgreSQL, often referred to as Postgres, is a powerful open-source relational database management system (RDBMS) known for its scalability, robustness, and extensibility. It offers advanced features like ACID compliance, support for complex data types, and support for both SQL and NoSQL data. PostgreSQL is highly regarded for its performance, security, and reliability, making it a popular choice for applications ranging from small startups to large enterprises. Its active developer community continuously enhances and maintains the software. PostgreSQL is an excellent choice for data storage, analysis, and management in various domains, including web applications, data warehousing, and geospatial applications.
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Practice Test
51. In PostgreSQL, what does a common table expression (CTE) allow you to do?
A. Define temporary result sets within a query
B. Create temporary tables
C. Define table schemas
D. Create indexes on tables
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Answer: Define temporary result sets within a query
52. What is the purpose of the "WINDOW" clause in a PostgreSQL query?
A. To define a window frame for window functions
B. To specify the window size
C. To restrict access to certain rows
D. To create a virtual table
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Answer: To define a window frame for window functions
53. Which SQL clause is used to pivot rows into columns in PostgreSQL?
A. PIVOT
B. UNPIVOT
C. CROSS JOIN
D. CASE
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Answer: CASE
54. What is the purpose of the "LATERAL" keyword in a PostgreSQL query?
A. To reference columns from the preceding tables in a subquery
B. To order the result set
C. To create subqueries
D. To limit the number of rows returned
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Answer: To reference columns from the preceding tables in a subquery
55. What is a recursive common table expression (RCTE) in PostgreSQL used for?
A. To handle hierarchical data and recursive queries
B. To create temporary tables
C. To join multiple tables
D. To define primary keys
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Answer: To handle hierarchical data and recursive queries
56. What is the purpose of the "EXISTS" operator in a PostgreSQL query?
A. To check if a subquery returns any rows
B. To filter rows with specific criteria
C. To join multiple tables
D. To order the result set
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Answer: To check if a subquery returns any rows
57. In PostgreSQL, what does the "OVER" clause do in the context of window functions?
A. Defines the window frame for the function
B. Specifies the window size
C. Orders the result set
D. Groups the rows by a specific column
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Answer: Defines the window frame for the function
58. What is the purpose of the "UNION" operator in PostgreSQL?
A. Combines the result sets of two or more SELECT statements, removing duplicates
B. Joins multiple tables based on a common column
C. Calculates the average of a numeric column
D. Filters rows based on a specified condition
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Answer: Combines the result sets of two or more SELECT statements, removing duplicates
59. What does the "FULL OUTER JOIN" do in a PostgreSQL query?
A. Retrieves all records where there is a match in either the left or right table
B. Retrieves records that exist in both the left and right tables
C. Retrieves records that exist only in the left table
D. Retrieves records that exist only in the right table
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Answer: Retrieves all records where there is a match in either the left or right table
60. What does the "WITH ORDINALITY" option do when used with the "UNNEST" function in PostgreSQL?
A. Adds an ordinal position to each element in an array
B. Orders the result set based on a specific column
C. Adds a unique identifier to each row
D. Filters rows based on a specified condition
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Answer: Adds an ordinal position to each element in an array
