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SQL Joins and Query Techniques: INNER, OUTER, CROSS, and Grouping
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What is the purpose of an SQL JOIN clause?
To combine rows from two or more tables based on a common field.
What does an INNER JOIN do? Returns combined column values of two tables based on the join condition.
What is a CROSS JOIN? Produces the Cartesian product of rows from two tables.
What is the result size of a CROSS JOIN?
The number of rows in the first table multiplied by the number of rows in the second table.
What does a LEFT OUTER JOIN return?
All rows from the left table and matched rows from the right table, filling unmatched rows with nulls.
What does a RIGHT OUTER JOIN return?
All rows from the right table and matched rows from the left table.
What is a FULL OUTER JOIN? Returns all rows when there is a match in one of the tables.
What is a NATURAL JOIN? An implicit join that uses common columns from both tables without an explicit join condition.
How does INNER JOIN differ from CROSS JOIN in terms of efficiency?
INNER JOIN is more efficient as it filters results based on the join condition, while CROSS JOIN can become inefficient with larger tables.
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What is the result of using a WHERE clause with a JOIN?
It filters the results based on specified conditions before the join is applied.
What does the AVG function calculate?
Calculates the average of all values in numeric columns.
What does the MIN function return? Returns the minimum value from a set of values.
What does the MAX function return? Returns the maximum value from a set of values.
What is a limitation of SQL built-in functions?
You cannot combine table column names with an SQL built-in function.
What is the significance of the GROUP BY clause?
It groups rows that have the same values in specified columns into summary rows.
What is the purpose of the SQL DATEDIFF() function?
Calculates the difference between two date values.
