This article provides a comprehensive guide to using SQLite expressions. We’ll explore the different types of expressions, see relevant examples, and learn how to use expressions across various SQL statements. By the end, you’ll know how to use SQLite expressions for your projects and tasks.
What's in this article
What are SQLite Expressions?
SQLite expressions are constructs that evaluate a single data value. They allow you to define calculations, manipulate data, and add logic within SQL statements.
There are several types of expressions in SQLite:
- Arithmetic expressions: Perform mathematical calculations using operators like addition and multiplication.
- Comparison expressions: Evaluate conditions and return boolean values using comparison operators.
- Logical expressions: Combine multiple boolean expressions using logical operators like AND, OR.
- String expressions: Operate on textual strings using functions or concatenation.
- Date and time expressions: Use built-in date functions to work with dates and times.
With these expression types, you can transform and analyze data in powerful ways directly within your SQL queries.
Arithmetic expressions allow you to perform basic mathematical operations and functions.
The basic arithmetic operators supported are:
- Addition (
- Subtraction (
- Multiplication (
- Division (
These allow you to construct expressions that evaluate to numeric values, like
2 + 3 or
revenue - expenses.
Some handy mathematical functions are also available:
ABS(x)– Returns the absolute value of x
ROUND(x)– Rounds x to the nearest integer
CEIL(x)– Rounds x up to the next largest integer
These functions expand your options for numeric calculations.
Here are some simple example expressions:
-- Simple calculations SELECT 2 * 3; -- Returns 6 SELECT MAX(price * quantity) FROM OrderDetails; -- Calculates total price -- Using functions SELECT ROUND(15.7); -- Returns 16 SELECT ABS(amount) FROM Transactions; -- Gets the positive value
This demonstrates basic arithmetic expressions in action. The real utility comes from integrating them into more complex SQL queries, which we’ll see later.
Comparison expressions evaluate conditions and return boolean values. They allow you to test values against expected criteria.
The standard comparison operators are:
- Equal (
- Not Equal (
- Greater Than (
- Less Than (
Here are some example comparison expressions:
price = 100 orderDate <> '2020-01-01' quantity > 10 rating <= 5
These expressions are evaluated to either TRUE or FALSE, depending on the values.
Let’s see some comparisons in practice:
-- Comparing numbers SELECT productCode FROM Products WHERE price > 50; -- Comparing strings SELECT name FROM Contacts WHERE state != 'CA';
Here we filter records based on comparison logic. This is a common pattern with SQLite expressions.
Logical expressions allow you to combine multiple boolean (TRUE/FALSE) expressions using logic operators.
The logical SQLite operators are:
AND– Returns TRUE if both component expressions are TRUE
OR– Returns TRUE if either component expression is TRUE
NOT– Flips a boolean value (converts TRUE to FALSE)
quantity > 50 AND price < 10 inStock OR shippingDays < 3 NOT expired
These expressions evaluate to a boolean result by applying logical rules.
Some usage examples:
-- Combining conditions SELECT * FROM Products WHERE stockLevel > 10 AND price < 5; -- Negating conditions SELECT * FROM Orders WHERE NOT shipped;
Here we filter data by combining logical expressions. The
NOT operator is useful for inverting boolean checks.
String expressions allow you to manipulate textual strings.
The string concatenation operator in SQLite is
'Hello ' || 'world!' -- Returns 'Hello world!'
This joins together strings.
Some handy string functions are:
LENGTH(string)– Returns the length of a string
UPPER(string)– Converts string to upper case
LOWER(string)– Converts string to lower case
-- Concatenating strings SELECT firstName || ' ' || lastName AS fullName FROM Contacts; -- Changing case SELECT UPPER(companyName) FROM Companies; SELECT LOWER(streetName) FROM Addresses;
Here we transform strings using concatenation and string functions. This can help normalize inconsistent data formats.
Date and Time Expressions
Date and time expressions enable working with temporal values.
Some useful date/time functions are:
DATE(datetime)– Returns the date portion
TIME(datetime)– Returns the time portion
DATETIME(date, time)– Combines date and time
-- Extracting date parts SELECT DATE(orderDateTime) FROM Orders; -- Formatting dates SELECT DATETIME(orderDate, '12:00:00') FROM Orders;
This provides flexibility for extracting specific date or time components from datetimes.
Using Expressions in SQL Statements
Now that we’ve covered the basics of expressions, let’s see how they integrate into full SQL statements.
Expressions are commonly used in:
SELECT– Define calculated columns
WHERE– Filter by conditions
ORDER BY– Sort by expressions
GROUP BY– Group by computed values
HAVING– Filter groups by aggregate calculations
SELECT name, quantity * unitPrice AS totalPrice FROM OrderDetails WHERE totalPrice > 100 ORDER BY totalPrice DESC GROUP BY name HAVING SUM(quantity) > 10;
Here expressions are leveraged across clauses for filtering, sorting, grouping, and aggregations.
When using expressions, keep in mind:
- Avoid SQL injection by using parameters instead of injecting raw values.
- Use prepared statements with bound parameters to safely insert data.
- Strive for clean, readable code with descriptive comments.
Adhering to best practices will help keep your SQLite databases secure and maintainable.
SQLite expressions provide powerful capabilities for transforming, filtering, and analyzing data within SQL queries. The major types of expressions include arithmetic, comparison, logic, string, and date/time.
Mastering expressions will allow you to tap into more of SQLite’s capabilities and efficiently manipulate data. Important use cases include calculated columns, conditional filtering, sorting, grouping, and aggregations.
You can build robust applications with SQLite by following security best practices like prepared statements and writing clean, readable code. The official SQLite documentation contains even more expression examples and syntax options, enabling you to continue enhancing your skills.