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Questions and Answers
What is crucial when combining tables to ensure accurate reporting?
What is crucial when combining tables to ensure accurate reporting?
What is the primary purpose of a subquery in SQL?
What is the primary purpose of a subquery in SQL?
What is the name of the chapter that covers SQL fundamentals?
What is the name of the chapter that covers SQL fundamentals?
What is the outcome of a subquery in SQL?
What is the outcome of a subquery in SQL?
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Why is it essential to write code that can adapt to changing data?
Why is it essential to write code that can adapt to changing data?
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What is the term for a query that is embedded within the WHERE clause of another SQL query?
What is the term for a query that is embedded within the WHERE clause of another SQL query?
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What is the purpose of the having clause in a select statement?
What is the purpose of the having clause in a select statement?
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What happens when you join multiple tables together?
What happens when you join multiple tables together?
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What is the best approach when combining more than two tables?
What is the best approach when combining more than two tables?
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What is the join condition used for?
What is the join condition used for?
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What happens to unmatched rows in an inner join?
What happens to unmatched rows in an inner join?
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What is the main difference between inner joins and outer joins?
What is the main difference between inner joins and outer joins?
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When designing a database, how are tables often designed to be joined?
When designing a database, how are tables often designed to be joined?
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What can SQL use to get to the result more efficiently?
What can SQL use to get to the result more efficiently?
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What is the purpose of using a table of constants in a SQL query?
What is the purpose of using a table of constants in a SQL query?
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Why is punctuation important in SQL queries?
Why is punctuation important in SQL queries?
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What is the significance of case sensitivity in Oracle?
What is the significance of case sensitivity in Oracle?
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What is the purpose of using views in SQL?
What is the purpose of using views in SQL?
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What is three-valued logic in SQL?
What is three-valued logic in SQL?
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What is the difference between a table and a view?
What is the difference between a table and a view?
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What is the benefit of saving the result of a select statement in a table?
What is the benefit of saving the result of a select statement in a table?
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What is the purpose of modifying data in a table?
What is the purpose of modifying data in a table?
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Study Notes
Combining Tables
- There are several ways to combine tables, including inner join, three types of outer join, union, cross join, and self join.
- The way tables are combined affects the results of later reporting, so it's essential to do it correctly.
- Code should be written to handle any data that could be put into the tables, not just the current data.
Subqueries
- A subquery or inner query or nested query is a query within another SQL query, embedded within the WHERE clause.
- Subqueries return data used in the main query as a condition to further restrict the data to be retrieved.
- The HAVING clause of the SELECT statement can be used to drop rows from a result table containing summarized data.
Inner Joins
- An inner join is the most frequently used method to combine several tables together.
- When joining tables, the tables are combined to form a new larger table, and then data is selected or summarized from this new table.
- The inner join is a method to combine several tables together, other methods include outer joins and unions.
- When combining more than two tables, the best approach is to join only two tables at a time, and then repeat the process.
- The join condition is the rule that matches rows of one table with rows of another table.
SQL Fundamentals
- Computers use the words AND, OR, and NOT in a precise way that is different from how they are used in English.
- Punctuation is very important in SQL, and some databases are case-sensitive.
- SQL uses three-valued logic, which means there can be nulls in the data.
Saving Results and Creating Tables
- The result of any select statement can be saved in a table or view.
- A table saves the actual data as it is at one particular moment in time, while a view saves the select statement and runs it again whenever the view is used.
- A table contains fixed data unless changed, while a view contains data that is constantly updated.
- One view can be built from another view.
- Restrictions apply when modifying data in a table, and tables can be created and modified using SQL.
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Description
Learn about SQL subqueries and how to write flexible code that adapts to changing data. Understand the importance of correct table combinations for accurate reporting.