What types of physical table joins exist (Hash Join, Merge Join, Nested Loop)?
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Data Engineer
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What salary are you expecting?
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Have you worked with data vitrines (DWH layer)?
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Расскажи про пару своих наиболее существенных задач, связанных с качеством данных.
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What is CROSS JOIN? Have you worked with it?
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If you join transactions with clients by client_id and date_start (without BETWEEN), what will be captured in the result?
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Why are you looking for a new job now, do you want to change your job?
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What types of JOINs do you know? (logical)
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Is it possible to read data in parallel from a single Parquet file in Spark, or only with one core in one task?
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What are the advantages and disadvantages of row-oriented and column-oriented databases? Which is more effective for grouping and aggregation?
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Tell us about yourself — work experience, technology stack.
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If the executor has 10 cores, how many Tasks will be executed in parallel at the same time?
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Describe window functions in the most expanded form: what keywords are used and what each is responsible for.
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-- Given a table named numbers with one column num (integers, possibly repeating). -- Write an SQL query that splits the numbers into two columns: -- even – even numbers (sorted in ascending order) -- odd – odd numbers (sorted in ascending order) -- The numbers should be arranged row by row: in the first row – the first even and the first odd, -- in the second row – the second even and the second odd, and so on. -- If one group has more numbers than the other, the missing places should be filled with NULL. -- Original table -- num -- --------- -- [phone] -- Result of the query -- even | odd -- -----|----- -- 2 | 1 -- 4 | 3 -- 6 | 5 -- 8 | 7 -- 10 | 9 -- NULL | 11 -- NULL | 11
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Tell about your understanding of data quality — have you had experience working in this area?
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How does Nested Loop Join work and what is its algorithmic complexity? What about the complexity of the other three algorithms?
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What is an index? How does a clustered index differ from a non-clustered index?
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What physical JOINs do you know?
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Give a high-level overview of the Spark architecture: what components are there and how do they interact when executing an SQL query?
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What is LEFT SEMI JOIN and LEFT ANTI JOIN in Spark SQL, have you ever used them?
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