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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;
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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;
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What is a window function?
Operates over a set of rows related to the current row.
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How to rank data using a window function?
SELECT column1, RANK() OVER (ORDER BY column1) AS rank FROM table_name;
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How to calculate cumulative sum for a column?
SELECT column1, SUM(column1) OVER (ORDER BY column1) AS cumulative_sum FROM table_name;
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What is the difference between UNION and UNION ALL?
UNION removes duplicates; UNION ALL keeps duplicates.
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How to import a CSV file into pandas DataFrame?
import pandas as pd; df = pd.read_csv('file.csv')
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How to handle missing data in pandas?
df.fillna(value=0, inplace=True)
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How to use list comprehensions in Python?
numbers = [x for x in range(10) if x % 2 == 0]
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What is the difference between apply() and map() in pandas?
apply() is for row/column-wise; map() is element-wise.
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How to visualize data using matplotlib?
import matplotlib.pyplot as plt; sns.histplot(df['column'], bins=10); plt.show()
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How to calculate correlation in pandas?
def calculate_correlation(df, col1, col2): return df[col1].corr(df[col2])
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How to use VLOOKUP in Excel?
=VLOOKUP(A2, Sheet2!A:B, 2, FALSE)
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How to use XLOOKUP in Excel?
=XLOOKUP(A2, Sheet2!A:A, Sheet2!B:B)
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What is the difference between absolute and relative references?
Absolute (\(A\)1) does not change; Relative (A1) adjusts.
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How to create a pivot table in Excel?
Select the data > Insert > PivotTable.
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What can you do with a pivot table?
Summarize data, perform aggregation, group data.
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How to use conditional formatting in Excel?
Select cells > Home > Conditional Formatting > New Rule.
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How to use IF, AND, OR functions in Excel?
=IF(AND(A1 > 10, OR(B1 < 5, C1 = 20)), 'Pass', 'Fail')
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How to create a calculated column in Power BI?
Use DAX: New Column = Table[column1] + Table[column2].
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What is the difference between slicer and filter in Power BI?
Slicer is visual; filter is backend-level.
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How to create relationships between tables in Power BI?
Manage relationships under 'Model' view.
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How to set up row-level security in Power BI?
Define roles in 'Modeling' > Manage Roles.
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What is the purpose of CALCULATE and FILTER in DAX?
CALCULATE() changes context; FILTER() applies filters.
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How do you create a calculated field in Tableau?
Go to 'Analysis' > 'Create Calculated Field'.
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What types of calculations can you perform in Tableau?
Basic arithmetic, logical tests, aggregate functions.
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What is a parameter in Tableau?
A dynamic input that users can control to change views.
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How can parameters be used in Tableau?
To filter views, change calculations, or control data shown.
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How do you create a dual-axis chart in Tableau?
Drag two measures to Rows or Columns, right-click an axis, select 'Dual-Axis'.
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How to optimize a Tableau dashboard for performance?
Use extracts, reduce filters, limit high-granularity data, minimize worksheets.
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How do you create a custom date filter in Tableau?
Use a calculated field with date parameters to filter ranges.
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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;
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;
What is a window function?
Operates over a set of rows related to the current row.
How to rank data using a window function?
SELECT column1, RANK() OVER (ORDER BY column1) AS rank FROM table_name;
How to calculate cumulative sum for a column?
SELECT column1, SUM(column1) OVER (ORDER BY column1) AS cumulative_sum FROM table_name;
What is the difference between UNION and UNION ALL?
UNION removes duplicates; UNION ALL keeps duplicates.
How to import a CSV file into pandas DataFrame?
import pandas as pd; df = pd.read_csv('file.csv')
How to handle missing data in pandas?
df.fillna(value=0, inplace=True)
How to use list comprehensions in Python?
numbers = [x for x in range(10) if x % 2 == 0]
What is the difference between apply() and map() in pandas?
apply() is for row/column-wise; map() is element-wise.
How to visualize data using matplotlib?
import matplotlib.pyplot as plt; sns.histplot(df['column'], bins=10); plt.show()
How to calculate correlation in pandas?
def calculate_correlation(df, col1, col2): return df[col1].corr(df[col2])
How to use VLOOKUP in Excel?
=VLOOKUP(A2, Sheet2!A:B, 2, FALSE)
How to use XLOOKUP in Excel?
=XLOOKUP(A2, Sheet2!A:A, Sheet2!B:B)
What is the difference between absolute and relative references?
Absolute (\(A\)1) does not change; Relative (A1) adjusts.
How to create a pivot table in Excel?
Select the data > Insert > PivotTable.
What can you do with a pivot table?
Summarize data, perform aggregation, group data.
How to use conditional formatting in Excel?
Select cells > Home > Conditional Formatting > New Rule.
How to use IF, AND, OR functions in Excel?
=IF(AND(A1 > 10, OR(B1 < 5, C1 = 20)), 'Pass', 'Fail')
How to create a calculated column in Power BI?
Use DAX: New Column = Table[column1] + Table[column2].
What is the difference between slicer and filter in Power BI?
Slicer is visual; filter is backend-level.
How to create relationships between tables in Power BI?
Manage relationships under 'Model' view.
How to set up row-level security in Power BI?
Define roles in 'Modeling' > Manage Roles.
What is the purpose of CALCULATE and FILTER in DAX?
CALCULATE() changes context; FILTER() applies filters.
How do you create a calculated field in Tableau?
Go to 'Analysis' > 'Create Calculated Field'.
What types of calculations can you perform in Tableau?
Basic arithmetic, logical tests, aggregate functions.
What is a parameter in Tableau?
A dynamic input that users can control to change views.
How can parameters be used in Tableau?
To filter views, change calculations, or control data shown.
How do you create a dual-axis chart in Tableau?
Drag two measures to Rows or Columns, right-click an axis, select 'Dual-Axis'.
How to optimize a Tableau dashboard for performance?
Use extracts, reduce filters, limit high-granularity data, minimize worksheets.
How do you create a custom date filter in Tableau?
Use a calculated field with date parameters to filter ranges.
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