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Questions and Answers
What is the result of executing a DELETE query without a WHERE clause on the CUSTOMERS table?
What would happen if an UPDATE query is executed without a WHERE clause?
Which operators can be used to specify conditions in a WHERE clause?
How do you write an UPDATE query to change the ADDRESS for a specific customer in the CUSTOMERS table?
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What role does the WHERE clause serve when using a SELECT statement?
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What does the acronym CRUD represent in the context of a relational database?
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Which statement correctly describes the purpose of the INSERT INTO statement?
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In SQL, what is the output of a SELECT query?
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What happens when a DELETE query is executed without a WHERE clause?
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Which of the following is NOT a necessary component of an SQL INSERT INTO statement?
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Which SQL clause can be used in DELETE statements to specify which records to remove?
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What is the result of executing a SELECT statement without specifying any fields?
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If you want to combine multiple conditions in a DELETE query, which operators can you use?
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Study Notes
Data Manipulation Language (DML)
- DML is the subset of SQL used to manage data in a database.
- DML includes the following operations: Create, Read, Update, and Delete (CRUD).
Insert Query
- Purpose: To add new records to a database table.
-
Syntax:
INSERT INTO <table_name> (<column1>, <column2>, ... , <columnN>) VALUES (<value1>, <value2>, ... , <valueN>); -
Example:
INSERT INTO CUSTOMERS (ID, Name, Salary) VALUES (1, 'John', 50000); -
Alternative Syntax (optional):
INSERT INTO <table_name> VALUES (<value1>, <value2>, ... , <valueN>);(If values are provided for all columns in the table in the correct order) -
Note: The order of values provided in the
VALUESclause must match the order of the columns specified in the query.
Select Query
- Purpose: To retrieve data from a database table.
-
Syntax:
SELECT <column1>, <column2>, ... , <columnN> FROM <table_name>; -
Example:
SELECT ID, Name, Salary FROM CUSTOMERS; -
Note: You can select specific columns, all columns (
SELECT *), or a combination thereof. The result is a result-set, which is a table representation of the data.
Delete Query
- Purpose: To remove existing records from a database table.
-
Syntax:
DELETE FROM <table_name> WHERE <condition(s)>; -
Examples:
-
DELETE FROM CUSTOMERS WHERE ID = 6;(Deletes a specific record) -
DELETE FROM CUSTOMERS;(Deletes all records from the table)
-
-
Note: The use of a
WHEREclause is crucial for deleting specific records.
Update Query
- Purpose: To modify the data of existing records in a database table.
-
Syntax:
UPDATE <table_name> SET <column1> = <value1>, <column2> = <value2>, ... WHERE <condition(s)>; -
Examples:
-
UPDATE CUSTOMERS SET ADDRESS = 'New Address' WHERE ID = 6;(Updates the address of a specific record) -
UPDATE CUSTOMERS SET ADDRESS = 'New Address', SALARY = 60000;(Updates multiple columns for all records)
-
-
Note: Like
DELETE, the use ofWHEREclause is essential for specifying which records to modify.
Where Clause
- Purpose: To filter and restrict the data returned by the query.
-
Syntax: Used within
SELECT,UPDATE, andDELETEstatements. -
Syntax (example):
WHERE <condition(s)> -
Examples (Within
SELECT):-
SELECT ID, Name FROM CUSTOMERS WHERE SALARY > 50000;(Returns data only for customers with salary greater than 50000) -
SELECT ID, Name FROM CUSTOMERS WHERE City = 'London' AND Salary > 40000;(Returns data for customers who meet both conditions)
-
-
Notes:
- The
WHEREclause enables targeted data retrieval based on specified conditions. - It is used to filter and extract subsets of data from a table.
- Use of comparison operators (>, <, =, >=, <=, !=), logical operators (AND, OR, NOT), and parentheses can further refine the conditions in
WHEREclause.
- The
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Description
Test your knowledge of Data Manipulation Language (DML) in SQL. This quiz covers essential operations such as Create, Read, Update, and Delete (CRUD), along with syntax for Insert and Select queries. Perfect for anyone looking to enhance their database management skills.
