AND, OR and NOT Operators in SQL
In SQL, the AND, OR, and NOT operators are used to combine multiple conditions in a SELECT, INSERT, UPDATE, or DELETE statement. These operators are used to filter records based on multiple conditions.
Here is a brief overview of how each operator works:
- AND operator: The AND operator returns true if all the conditions separated by AND are true. For example, the following statement will return rows where the color is 'red' and the price is greater than 10:
SELECT * FROM products WHERE color = 'red' AND price > 10;
- OR operator: The OR operator returns true if any of the conditions separated by OR are true. For example, the following statement will return rows where the color is 'red' or the price is greater than 10:
SELECT * FROM products WHERE color = 'red' OR price > 10;
- NOT operator: The NOT operator negates the condition following it. For example, the following statement will return rows where the color is not 'red':
SELECT * FROM products WHERE NOT color = 'red';
Combined/Group Operators (AND, OR, NOT)
It's also possible to use parentheses to group conditions and control the order of precedence. For example:
SELECT * FROM products WHERE (color = 'red' OR color = 'blue') AND price > 10;
This statement will return rows where the color is either 'red' or 'blue', and the price is greater than 10.
When using the AND, OR, and NOT operators in SQL, it is important to use parentheses to clearly define the order of operations. For example, the statement
SELECT * FROM table WHERE column1 = value1 AND column2 = value2 OR column3 = value3could be interpreted in multiple ways depending on the order of operations. To ensure that it is clear that column1 and column2 must be true and column3 must be false, the statement should be written as
SELECT * FROM table WHERE (column1 = value1 AND column2 = value2).
It is also important to use uppercase for the operators. ANSI SQL standard use uppercase for the operators (AND, OR, NOT), so it's better to use uppercase to avoid confusion.
Another best practice is to use the NOT operator sparingly, as negating a large number of conditions can make the query harder to understand.
Additionally, it is important to use indexes on the columns that are being used in the WHERE clause to improve the performance of the query
Finally, It's also good idea to test your query using EXPLAIN command to check the query execution plan and indexes that being used by the query, This will give you an insight on how to improve your query.
ORoperators are used to filter records based on more than one condition.
ANDoperator displays a record if all the conditions separated by AND are
ORoperator displays a record if any of the conditions separated by
NOToperator displays a record if the condition(s) is
You now have the ability to retrieve the exact data you want. This opens up many possibilities.
You can use the
WHEREclause in conjunction with
NOT, allowing you to be very precise with your SQL queries.
Using uppercase letters for SQL keywords and lowercase letters for everything else. This is a common practice that helps make your queries more readable.