SQLite String Concatenation: Joining Strings in Queries

Concatenating strings in SQLite allows you to combine text from multiple sources into a single string. This is useful for formatting output and generating readable strings from column data.

SQLite doesn’t have a built-in CONCAT() function like some other database systems. However, it provides the || operator to concatenate strings together in queries.

By the end, you’ll be an expert at combining text strings from different sources in your SQLite database. Let’s get started!

SQLite lets you easily join text strings together using the || concatenation operator. To concatenate two columns like first and last name, simply go SELECT FirstName || ‘ ‘ || LastName to join them with a space in between. Make sure to add formatting characters between columns so the values don’t run together. You can concat as many strings as you want by chaining multiple || operators. Overall, concatenation with || is a simple but powerful way to combine text from different sources in SQLite for formatting query output.

What is String Concatenation?

String concatenation refers to joining two or more string values together to produce a single string.

For example, you might concatenate a first name and last name column to generate a full name using the SELECT statement as follows:

SELECT 
  FirstName || ' ' || LastName AS FullName
FROM Employees;

This joins the FirstName and LastName columns together with a space in between.

Concatenation is useful any time you need to combine text from different sources. Common uses include:

• Generating readable combined strings from column data
• Adding formatting and text characters like spaces, commas, etc.
• Combining string literals and column values
• Creating delimiter-separated strings

SQLite lets you easily concatenate strings using the || operator.

Also read: SQLite AND Operator

Concatenating Strings with ||

To concatenate two or more strings in SQLite, use the || operator:

string1 || string2 || stringN

For example:

SELECT 'Hello' || 'World';

-- Result: HelloWorld

The || operator joins the strings on either side of it. You can use multiple || operators to concatenate multiple values:

SELECT 'Hello' || ' ' || 'World' || '!'; 

-- Result: Hello World!

The strings can be literal values like the above, or column names from a table:

SELECT 
  FirstName || ' ' || LastName AS FullName 
FROM Employees;

This joins the FirstName and LastName column values together, separating them with a space.

You can concatenate as many strings as you want by chaining || operators. The result is a single combined string.

Also read: SQLite OR Operator

Adding Spaces Between Columns

A common use for concatenation is joining column values with spaces between them. For example, to combine first and last name columns into a full name:

SELECT
  FirstName || ' ' || LastName AS FullName
FROM Employees;

This adds a space between the first and last names. Without that space, the names would run together:

-- Don't do this
SELECT
  FirstName || LastName AS FullName 
FROM Employees;

-- Result: JohnDoe instead of John Doe

Make sure to add formatting characters like spaces when concatenating column values.

Real-World Examples of String Concatenation

Concatenation becomes more useful when you’re working with actual data.

Here are some real-world examples of using || to combine strings from a database table.

Full Name from First and Last Name

A common use is generating a full name column by joining first and last name:

SELECT
  first_name || ' ' || last_name AS full_name
FROM employees;

Results:

This readable full name column comes from concatenating the first and last name with a space in between.

Address from Columns

You can also concatenate different address fields into a single string:

SELECT
  first_name || ' ' || last_name AS full_name,
  street || ' ' || city || ', ' || state || ' ' || zip AS address  
FROM customers;

Results:

The address column combines street, city, state, and zip together with the proper formatting.

Also read: SQLite Show Table Columns: A Detailed Guide

Delimiter-Separated List from Column

Another useful technique is creating a delimiter-separated list from a column.

For example, comma-separated tags:

SELECT
  name,
  tag1 || ', ' || tag2 || ', ' || tag3 AS tags
FROM products;

Results:

The tags column joins all the tag columns with commas between them.

You can use this to easily create delimited lists from column data.

Also read: SQLite Show Tables

Literal Strings and Column Values

You can mix literal strings with column values:

SELECT
  'Name: ' || first_name || ' ' || last_name
FROM customers;

Results:

This prepends a literal “Name: ” string before each full name result.

Mixing literals and column values lets you add text around your concatenated results.

Formatting Concatenated Strings

When joining text strings together, you’ll often want to add formatting:

• Spaces – Separate words and columns
• Commas – Create comma-separated lists
• Parentheses – Enclose parts of the string

Make sure to add any necessary formatting characters and punctuation when concatenating strings.

Here are some examples:

-- Space between first and last name
SELECT
  first_name || ' ' || last_name 
FROM employees;

-- Comma-separated list
SELECT
  category1 || ', ' || category2 || ', ' category3 AS categories
FROM products; 

-- Parentheses around area code
SELECT
  '(' || area_code || ')' || ' ' || prefix || '-' || line_number AS phone_number
FROM customers;

Take the time to format your concatenated strings for readability. Don’t just blindly smash columns together.

Concatenating NULL Values in SQLite

In SQLite, concatenating with a NULL value will also return NULL.

For example:

SELECT 
  first_name || ' ' || NULL
FROM employees;

If first_name is not NULL, but the second value is NULL, the entire result will become NULL.

To avoid this, you can wrap columns in COALESCE():

SELECT
  first_name || ' ' || COALESCE(middle_name, '')
FROM employees; 

COALESCE() will return the second argument '' if middle_name is NULL. This ensures a non-NULL value is concatenated.

Handling NULL values is an important consideration when concatenating strings.

GROUP_CONCAT() Alternative in SQLite

SQLite doesn’t have an aggregate function like MySQL’s GROUP_CONCAT() to concatenate column values into a string per group.

However, you can emulate this behavior by grouping and concatenating with ||:

SELECT
  product_category,
  MAX(product_name || ', ') AS products 
FROM products
GROUP BY product_category;

This will concatenate the product_name values into a comma-separated string for each product_category group.

The MAX() and comma ensure only a single delimited string is returned per group.

So while SQLite doesn’t have built-in support for aggregating concatenated strings, you can create your own version with || and GROUP BY.

Nested Subquery Alternative in SQLite

Another alternative to concatenation is using a nested subquery:

SELECT
  first_name || ' ' || last_name AS full_name,
  (SELECT GROUP_CONCAT(order_id) 
   FROM orders
   WHERE customer_id = customers.id) AS order_ids
FROM customers;   

The subquery concats the order_id values for each customer_id.

This can be easier than concatenating in the outer query for more complex examples. But it’s potentially less performant.

Subqueries are powerful and often underutilized in SQLite. They can be a good alternative to complex nested concatenations.

When to Use Concatenation

Here are some good use cases for concatenating strings in SQLite:

• Generating full names, addresses, or other combined strings
• Creating delimiter-separated lists from columns
• Formatting strings with additional text, spaces, commas, etc.
• Combining column data with literal strings
• Emulating MySQL’s GROUP_CONCAT() (to a degree)

In general, any time you need to combine multiple text strings, || concatenation is the easiest method.

Concatenation Tips

Here are some tips to use string concatenation effectively:

• Add formatting like spaces, commas, and parentheses between concatenated values
• Wrap columns in COALESCE() to handle NULL values
• Use MAX() and GROUP BY to emulate MySQL’s GROUP_CONCAT()
• Consider a subquery for more complex concatenated strings

Taking the time to properly format your concatenated strings will produce easy-to-read combined values.

Summary

Concatenation with || is the best way to join text strings in SQLite.

The key points to remember are:

• SQLite has no built-in CONCAT() function, but || serves the same purpose
• You can concatenate any number of strings together
• Make sure to add formatting like spaces between columns
• Handle NULL values with COALESCE() to avoid NULL concatenation results
• For aggregating concatenated strings, emulate GROUP_CONCAT() with the MAX() function

Learning to effectively use the || operator will unlock all kinds of useful ways to combine strings in your SQLite database.