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25 DA Questions
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Flashcards in this deck (31)

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  • How to find duplicate rows in a table?

    SELECT column1, column2, COUNT() FROM table_name GROUP BY column1, column2 HAVING COUNT() > 1;

    sql queries

  • How to perform a left join and filter out nulls?

    SELECT * FROM table1 LEFT JOIN table2 ON table1.id = table2.id WHERE table2.column IS NOT NULL;

    sql joins

  • What is a window function?

    Operates over a set of rows related to the current row.

    sql functions

  • How to rank data using a window function?

    SELECT column1, RANK() OVER (ORDER BY column1) AS rank FROM table_name;

    sql ranking

  • How to calculate cumulative sum for a column?

    SELECT column1, SUM(column1) OVER (ORDER BY column1) AS cumulative_sum FROM table_name;

    sql cumulative

  • What is the difference between UNION and UNION ALL?

    UNION removes duplicates; UNION ALL keeps duplicates.

    sql sets

  • How to import a CSV file into pandas DataFrame?

    import pandas as pd; df = pd.read_csv('file.csv')

    python pandas

  • How to handle missing data in pandas?

    df.fillna(value=0, inplace=True)

    python data

  • How to use list comprehensions in Python?

    numbers = [x for x in range(10) if x % 2 == 0]

    python comprehensions

  • What is the difference between apply() and map() in pandas?

    apply() is for row/column-wise; map() is element-wise.

    python pandas

  • How to visualize data using matplotlib?

    import matplotlib.pyplot as plt; sns.histplot(df['column'], bins=10); plt.show()

    python visualization

  • How to calculate correlation in pandas?

    def calculate_correlation(df, col1, col2): return df[col1].corr(df[col2])

    python correlation

  • How to use VLOOKUP in Excel?

    =VLOOKUP(A2, Sheet2!A:B, 2, FALSE)

    excel vlookup

  • How to use XLOOKUP in Excel?

    =XLOOKUP(A2, Sheet2!A:A, Sheet2!B:B)

    excel xlookup

  • What is the difference between absolute and relative references?

    Absolute (\(A\)1) does not change; Relative (A1) adjusts.

    excel references

  • How to create a pivot table in Excel?

    Select the data > Insert > PivotTable.

    excel pivot

  • What can you do with a pivot table?

    Summarize data, perform aggregation, group data.

    excel analysis

  • How to use conditional formatting in Excel?

    Select cells > Home > Conditional Formatting > New Rule.

    excel formatting

  • How to use IF, AND, OR functions in Excel?

    =IF(AND(A1 > 10, OR(B1 < 5, C1 = 20)), 'Pass', 'Fail')

    excel functions

  • How to create a calculated column in Power BI?

    Use DAX: New Column = Table[column1] + Table[column2].

    power_bi dax

  • What is the difference between slicer and filter in Power BI?

    Slicer is visual; filter is backend-level.

    power_bi filters

  • How to create relationships between tables in Power BI?

    Manage relationships under 'Model' view.

    power_bi relationships

  • How to set up row-level security in Power BI?

    Define roles in 'Modeling' > Manage Roles.

    power_bi security

  • What is the purpose of CALCULATE and FILTER in DAX?

    CALCULATE() changes context; FILTER() applies filters.

    power_bi dax

  • How do you create a calculated field in Tableau?

    Go to 'Analysis' > 'Create Calculated Field'.

    tableau calculations

  • What types of calculations can you perform in Tableau?

    Basic arithmetic, logical tests, aggregate functions.

    tableau calculations

  • What is a parameter in Tableau?

    A dynamic input that users can control to change views.

    tableau parameters

  • How can parameters be used in Tableau?

    To filter views, change calculations, or control data shown.

    tableau parameters

  • How do you create a dual-axis chart in Tableau?

    Drag two measures to Rows or Columns, right-click an axis, select 'Dual-Axis'.

    tableau charts

  • How to optimize a Tableau dashboard for performance?

    Use extracts, reduce filters, limit high-granularity data, minimize worksheets.

    tableau performance

  • How do you create a custom date filter in Tableau?

    Use a calculated field with date parameters to filter ranges.

    tableau filters