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Question-1. What is Kdb+?
Answer-1: Kdb+ is a high-performance columnar database with a built-in programming language called Q, designed for time-series data analysis.
Question-2. Who developed Kdb+?
Answer-2: Kdb+ was developed by Arthur Whitney and is maintained by KX Systems.
Question-3. What is K language?
Answer-3: K is a terse, high-performance programming language used as the foundation of Q, the query language of Kdb+.
Question-4. How is K different from Q?
Answer-4: K is lower-level and more concise, whereas Q is a more readable, SQL-like wrapper around K.
Question-5. What are the key features of Kdb+?
Answer-5: Columnar storage, in-memory processing, vectorized operations, and efficient handling of time-series data.
Question-6. What industries commonly use Kdb+?
Answer-6: Finance, telecommunications, IoT, and machine learning for real-time analytics.
Question-7. What is the main data structure in K?
Answer-7: The table, which is a collection of columnar vectors.
Question-8. How do you define a list in K?
Answer-8: L: (1;2;3;4)
Question-9. How do you create a dictionary in K?
Answer-9: D: (abc)!(10 20 30)`
Question-10. How do you create a table in K?
Answer-10: T: ([] sym:ABC; price:100 200 300)`
Question-11. How do you query data in Kdb+?
Answer-11: Using select statements: select from T where sym=A`
Question-12. What is a symbol in Kdb+?
Answer-12: A unique, interned string optimized for fast lookup.
Question-13. What is the difference between a list and a vector in K?
Answer-13: A vector is a homogeneous list of the same type, while a list can be heterogeneous.
Question-14. How do you perform a sum operation in K?
Answer-14: +/ 1 2 3 4 returns 10.
Question-15. What does count do in K?
Answer-15: Returns the number of elements in a list or table column.
Question-16. How do you define a function in K?
Answer-16: {x+y} defines an anonymous function adding two numbers.
Question-17. What is an adverb in K?
Answer-17: An operator that modifies a function, such as / (each-right) and \ (each-left).
Question-18. What is the purpose of the flip function?
Answer-18: Converts rows to columns and vice versa in a table.
Question-19. How do you get unique elements from a list?
Answer-19: Using distinct: distinct 1 2 2 3 3 4 returns 1 2 3 4.
Question-20. How do you join two tables in K?
Answer-20: Using lj (left join) or aj (asof join).
Question-21. What is the default date format in Kdb+?
Answer-21: YYYY.MM.DD
Question-22. How do you get the current date in Kdb+?
Answer-22: .z.D
Question-23. How do you get the current time in Kdb+?
Answer-23: .z.T
Question-24. What is a keyed table in Kdb+?
Answer-24: A table where one or more columns serve as unique keys for fast lookups.
Question-25. How do you define a keyed table?
Answer-25: kt: sym xkey ([] sym:AB; price:100 200)`
Question-26. What is a foreign key in Kdb+?
Answer-26: A reference to another table's primary key for relational integrity.
Question-27. How do you filter data in Kdb+?
Answer-27: select from T where price>100
Question-28. What is the group function used for?
Answer-28: Groups table rows by a specific column.
Question-29. How do you concatenate lists in K?
Answer-29: 1 2 3, 4 5 6 results in 1 2 3 4 5 6.
Question-30. How do you check the type of a variable in K?
Answer-30: type function: type 42 returns -7 (integer type).
Question-31. How does Kdb+ handle missing data?
Answer-31: Using :: (null values) or 0N (null numeric values).
Question-32. How do you remove duplicates in K?
Answer-32: distinct list
Question-33. What does exec do in Kdb+?
Answer-33: Extracts specific columns from a table.
Question-34. How do you append a row to a table?
Answer-34: T,: (new_sym; new_price).
Question-35. What does update do in K?
Answer-35: Modifies column values: update price:price*1.1 from T.
Question-36. How do you drop a column from a table?
Answer-36: delete column_name from table_name.
Question-37. What does except do in K?
Answer-37: Removes elements that match a given list.
Question-38. What is where used for in Kdb+?
Answer-38: To filter rows based on conditions.
Question-39. How do you create a time-series data column?
Answer-39: times: 10:00 + til 5.
Question-40. What is the difference between til and asc?
Answer-40: til n generates numbers from 0 to n-1, while asc sorts in ascending order.
Question-41. What is each used for in K?
Answer-41: Applies a function to each element in a list.
Question-42. How do you define a rolling sum in K?
Answer-42: xsum each 1 2 3 4 results in 1 3 6 10.
Question-43. What is fby in K?
Answer-43: Groups a list and applies a function per group.
Question-44. What is parse used for?
Answer-44: Converts strings to K expressions.
Question-45. How do you generate a range of dates in Kdb+?
Answer-45: 2019.01.01 + til 10.
Question-46. What is a partitioned database in Kdb+?
Answer-46: A method for storing large time-series datasets efficiently.
Question-47. How does Kdb+ store large datasets?
Answer-47: Using splayed tables and partitioned databases.
Question-48. How do you save a table in Kdb+?
Answer-48: .Q.dpft or .Q.fu functions.
Question-49. How do you start a Kdb+ process?
Answer-49: q in the command line.
Question-50. What is the advantage of Kdb+ over traditional databases?
Answer-50: It offers superior performance for time-series data through columnar storage and in-memory processing.
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