Podcast
Questions and Answers
What is the purpose of the HAVING clause in SQL?
What is the purpose of the HAVING clause in SQL?
- To filter the results after aggregation based on conditions (correct)
- To filter individual rows before aggregation
- To apply aggregate functions to each row
- To combine multiple tables into one result set
Which of the following statements correctly uses GROUP BY in conjunction with HAVING?
Which of the following statements correctly uses GROUP BY in conjunction with HAVING?
- SELECT course, MAX(max_enrl) FROM courses WHERE MAX(max_enrl) > 60
- SELECT product_id, COUNT(*) FROM products GROUP BY product_id HAVING COUNT(*) > 1 (correct)
- SELECT species, AVG(age) FROM animals HAVING AVG(age) > 10 GROUP BY species
- SELECT product_id, SUM(unit_price) FROM products HAVING SUM(unit_price) > 10
Which aggregate function is used to find the total capacity of courses in a SQL query?
Which aggregate function is used to find the total capacity of courses in a SQL query?
- AVG()
- SUM() (correct)
- MAX()
- COUNT()
What will the SELECT statement 'SELECT CONCAT(first_name, last_name) AS full_name FROM users;' return?
What will the SELECT statement 'SELECT CONCAT(first_name, last_name) AS full_name FROM users;' return?
Which of the following queries uses the HAVING clause correctly?
Which of the following queries uses the HAVING clause correctly?
In which part of a SQL query does the HAVING clause appear?
In which part of a SQL query does the HAVING clause appear?
What does the COALESCE() function do in SQL?
What does the COALESCE() function do in SQL?
Which SQL operation is mandatory in a SELECT statement?
Which SQL operation is mandatory in a SELECT statement?
What is the primary purpose of the HAVING clause in SQL?
What is the primary purpose of the HAVING clause in SQL?
Which operation allows you to group rows that have the same values in specified columns?
Which operation allows you to group rows that have the same values in specified columns?
Which SQL function is used to return a single value summarizing multiple rows?
Which SQL function is used to return a single value summarizing multiple rows?
What does the LIKE operator do in SQL?
What does the LIKE operator do in SQL?
What is the result of using the BETWEEN clause in an SQL query?
What is the result of using the BETWEEN clause in an SQL query?
How can you ensure that the results of an SQL query are unique?
How can you ensure that the results of an SQL query are unique?
Which clause is used to specify conditions for grouping in SQL?
Which clause is used to specify conditions for grouping in SQL?
What does the COUNT function do in SQL?
What does the COUNT function do in SQL?
Which wildcard character matches exactly one character in SQL string functions?
Which wildcard character matches exactly one character in SQL string functions?
What is the primary function of the WHERE clause in SQL?
What is the primary function of the WHERE clause in SQL?
When using GROUP BY, what happens to the number of rows in the result set?
When using GROUP BY, what happens to the number of rows in the result set?
Which aggregate function would you use to calculate the average value in a specific column?
Which aggregate function would you use to calculate the average value in a specific column?
What is the correct SQL statement to group data by 'category' and find the highest price in each category?
What is the correct SQL statement to group data by 'category' and find the highest price in each category?
Why should the LIMIT clause always be used with an ORDER BY clause?
Why should the LIMIT clause always be used with an ORDER BY clause?
What does the GROUP BY clause do in a SQL query?
What does the GROUP BY clause do in a SQL query?
Which of the following is NOT an aggregate function in SQL?
Which of the following is NOT an aggregate function in SQL?
How does the ORDER BY clause behave by default when sorting rows?
How does the ORDER BY clause behave by default when sorting rows?
What will happen if you omit the GROUP BY clause when using an aggregate function?
What will happen if you omit the GROUP BY clause when using an aggregate function?
In a SQL query, what is the primary function of the LIMIT clause?
In a SQL query, what is the primary function of the LIMIT clause?
Which of the following correctly describes a use case for the HAVING clause?
Which of the following correctly describes a use case for the HAVING clause?
What is the typical use of the GROUP BY clause in combination with aggregate functions?
What is the typical use of the GROUP BY clause in combination with aggregate functions?
Which SQL command is primarily used to summarize data across multiple rows?
Which SQL command is primarily used to summarize data across multiple rows?
How would you avoid getting unpredictable output when using LIMIT in a query?
How would you avoid getting unpredictable output when using LIMIT in a query?
Flashcards
HAVING Clause
HAVING Clause
Filters groups of rows in a SQL query based on aggregate functions (like SUM, AVG, COUNT).
HAVING Clause Example
HAVING Clause Example
Show courses with total capacity greater than 60; show products with total unit price greater than 10.
SQL SELECT Statement
SQL SELECT Statement
Selects data from a database table.
GROUP BY Clause
GROUP BY Clause
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Aggregate Functions
Aggregate Functions
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CONCAT()
CONCAT()
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SUBSTRING()
SUBSTRING()
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COALESCE()
COALESCE()
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ORDER BY Clause
ORDER BY Clause
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ASC
ASC
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DESC
DESC
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LIMIT Clause
LIMIT Clause
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SUM aggregate function
SUM aggregate function
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AVG aggregate function
AVG aggregate function
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MAX aggregate function
MAX aggregate function
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MIN aggregate function
MIN aggregate function
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WHERE clause
WHERE clause
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SELECT statement
SELECT statement
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Table
Table
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Column
Column
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Row
Row
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SELECT *
SELECT *
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FROM Clause
FROM Clause
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LIKE Operator
LIKE Operator
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BETWEEN Operator
BETWEEN Operator
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COUNT Function
COUNT Function
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DISTINCT Keyword
DISTINCT Keyword
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Study Notes
Lecture 09: Select Statement and Clauses
- The lecture covers Select Statements and Clauses in MySQL.
- The outline includes Recap, Clauses, and More Functions.
- The example provided shows a SELECT statement to retrieve specific columns (customer_id, first_name, last_name) from a customer table.
Select Statement Example
- The example retrieves columns customer_id, first_name, and last_name.
- The data is sourced from the "customer" table.
- Sample data is provided, including customer IDs, names, and other data elements.
Select Statement - Select All
- The example includes a query to select all columns from the "customer" table.
- Data includes customer ID, first name, last name, joined date, birth date, phone, address, city, state, and customer points.
- Data shows various values for each column illustrating the structure of the database table.
Clause - Order
- The SELECT and FROM clauses are fundamental to a SELECT statement.
- These two clauses are the only required components of a query.
Count and Distinct
- The COUNT function returns the total number of rows in a table.
- The DISTINCT keyword filters out duplicate values.
WHERE Clause - Condition
- The WHERE clause filters results based on conditions.
- It uses Boolean expressions and logical operators.
- An example shows selecting rows where the phone number is not NULL to remove any missing data.
WHERE Clause - Operations
- The WHERE clause allows various operations.
- These operations include LIKE, BETWEEN, IN, NULL, comparisons, AND, and OR.
WHERE Clause - LIKE operation
- The LIKE operation matches a string against a pattern.
- Wildcard characters, %, are used to match any sequence of zero or more characters, and _, for any single character.
WHERE Clause - BETWEEN
- The BETWEEN operator filters rows within a specified range.
- It can be used with numbers and expressions.
WHERE Clause - IN
- The IN operator filters rows based on a list.
- It is used to compare values to a comma-separated list.
WHERE Clause - NULL
- The IS NULL operator checks if a value is null ensuring correct handling of missing data.
WHERE Clause - Comparison Operators
- Various comparison operators (e.g., =, <>, <, >, <=, >=) can be used with the WHERE clause to filter data.
WHERE Clause - AND
- The AND operator combines multiple conditions in a WHERE clause, resulting in only rows matching all conditions.
WHERE Clause - OR
- The OR operator allows multiple conditions to be present in WHERE clause, allowing a row to be included if any condition is met.
HAVING Clause
- The HAVING clause filters groups of rows based on conditions.
- It works in conjunction with the GROUP BY clause.
Functions - CONCAT()
- The CONCAT() function concatenates strings into one.
Functions - GROUP_CONCAT()
- The GROUP_CONCAT() function concatenates values from multiple rows within a group, defined by the GROUP BY clause.
Functions - SUBSTRING()
- The SUBSTRING() function extracts a portion of a string.
- Providing the starting position and the length.
Functions - COALESCE()
- The COALESCE() function returns the first non-NULL value in a list of expressions, allowing to handle missing or null values (in tables).
Functions - ROUND()
- The ROUND() function rounds a numeric value to a specific number of decimal places.
Order of Clauses
- The standard order for SQL clauses:
- SELECT
- FROM
- WHERE (optional)
- GROUP BY (optional)
- HAVING (optional)
- ORDER BY (optional)
- LIMIT (optional)
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