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Questions and Answers
Which of the following is NOT a type of inner join?
Which of the following is NOT a type of inner join?
- Cross-join
- Natural join
- Outer join (correct)
- Equi-join
What is the danger of using natural join in large databases?
What is the danger of using natural join in large databases?
- It can add a new column named the same as another column in the other table. (correct)
- It can cause data to be duplicated in the resulting table.
- It can cause NULL values to be included in the resulting table.
- It can result in slow performance or server crashes.
Which SQL implementations use hash joins or sort-merge joins instead of computing the Cartesian product?
Which SQL implementations use hash joins or sort-merge joins instead of computing the Cartesian product?
- All SQL implementations
- The text does not specify
- Only Microsoft T-SQL and IBM DB2
- Only PostgreSQL and MySQL (correct)
When should inner join be used with caution?
When should inner join be used with caution?
What is the difference between equi-join and natural join?
What is the difference between equi-join and natural join?
Which SQL notation for expressing joins is no longer considered a best practice?
Which SQL notation for expressing joins is no longer considered a best practice?
When can a left outer join be substituted for an inner join?
When can a left outer join be substituted for an inner join?
Which databases support natural joins?
Which databases support natural joins?
What is the downside of using inner join in large volume queries with database functions in an SQL Where clause?
What is the downside of using inner join in large volume queries with database functions in an SQL Where clause?
Which of the following is NOT a type of inner join?
Which of the following is NOT a type of inner join?
What is the danger of using natural join in large databases?
What is the danger of using natural join in large databases?
Which SQL implementations use hash joins or sort-merge joins instead of computing the Cartesian product?
Which SQL implementations use hash joins or sort-merge joins instead of computing the Cartesian product?
When should inner join be used with caution?
When should inner join be used with caution?
What is the difference between equi-join and natural join?
What is the difference between equi-join and natural join?
Which SQL notation for expressing joins is no longer considered a best practice?
Which SQL notation for expressing joins is no longer considered a best practice?
When can a left outer join be substituted for an inner join?
When can a left outer join be substituted for an inner join?
Which databases support natural joins?
Which databases support natural joins?
What is the downside of using inner join in large volume queries with database functions in an SQL Where clause?
What is the downside of using inner join in large volume queries with database functions in an SQL Where clause?
Which type of join is a special case of an equi-join?
Which type of join is a special case of an equi-join?
What are the two ways to express joins in SQL?
What are the two ways to express joins in SQL?
Which type of join should be used with caution when joining tables on columns that can contain NULL values?
Which type of join should be used with caution when joining tables on columns that can contain NULL values?
What are the three types of inner joins?
What are the three types of inner joins?
Which databases support natural joins?
Which databases support natural joins?
What can be used instead of an inner join when the join columns in one table may contain NULL values?
What can be used instead of an inner join when the join columns in one table may contain NULL values?
What is the danger associated with using natural joins in large databases?
What is the danger associated with using natural joins in large databases?
What is the difference between a hash join and a sort-merge join?
What is the difference between a hash join and a sort-merge join?
When can inner join be safely used in a database?
When can inner join be safely used in a database?
Study Notes
Understanding Inner Join in SQL
- Inner join requires matching column values in two tables and combines their values based on the join-predicate.
- Actual SQL implementations use hash joins or sort-merge joins instead of computing the Cartesian product, which is slower and requires a large amount of memory.
- SQL specifies two ways to express joins - explicit join notation and implicit join notation, but the latter is no longer considered a best practice.
- Inner join should be used with caution when joining tables on columns that can contain NULL values.
- Inner join can only be safely used in a database that enforces referential integrity or where join columns are guaranteed not to be NULL.
- A left outer join can be substituted for an inner join when the join columns in one table may contain NULL values.
- Inner join can result in slow performance or server crashes when used in large volume queries with database functions in an SQL Where clause.
- One can classify inner joins as equi-joins, natural joins, or cross-joins.
- An equi-join uses only equality comparisons in the join-predicate, while a natural join is a special case of equi-join.
- The natural join combines all tuples in two tables that are equal on their common attribute names, but it is considered dangerous and not recommended for use in large databases.
- Most experts discourage the use of NATURAL JOINs due to the danger of inadvertently adding a new column named the same as another column in the other table.
- PostgreSQL, MySQL, and Oracle support natural joins, while Microsoft T-SQL and IBM DB2 do not.
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Description
Test your knowledge of Inner Join in SQL with this informative quiz. Learn about the different types of inner joins, their advantages and disadvantages, and when to use them. Understand the implications of using inner join on tables with NULL values and explore the alternative options available. Know the difference between equi-joins, natural joins, and cross-joins. Take this quiz to enhance your understanding of SQL and improve your database querying skills.
