SQL String Concatenation Across Databases

By Sharon Ben-Moshe · August 21, 2026 · 2 min read

Sharon Ben-Moshe is the founder of sqlfmt, a browser-based SQL formatter and validator with misspelled-keyword suggestions across PostgreSQL, MySQL, SQLite, SQL Server, and BigQuery.

Concatenate SQL strings with || or CONCAT, but NULL behavior differs by database. See portable patterns for PostgreSQL, MySQL, SQL Server, and BigQuery.

Quick answer

SQL string concatenation is not fully portable. PostgreSQL and BigQuery support `||`; MySQL, SQL Server, and BigQuery support CONCAT. The important difference is NULL handling: check the documented behavior of the chosen function before building labels, keys, or search text.

FAQs

What operator concatenates strings in SQL?

The `||` operator concatenates strings in PostgreSQL and BigQuery. Other databases also offer functions such as CONCAT, so confirm the target dialect before choosing syntax.

Does CONCAT ignore NULL values?

It depends on the database. SQL Server CONCAT converts NULL values to empty strings, while MySQL CONCAT returns NULL when an argument is NULL. Check the product documentation and make the required behavior explicit.

Why use COALESCE with SQL concatenation?

COALESCE can supply an empty string for an optional value, making the intended NULL behavior visible. It also makes test cases for incomplete names, addresses, or labels easier to reason about.

Is + a safe string concatenation operator in SQL?

Not as a portable choice. SQL Server supports + for strings, but type precedence and settings can affect behavior. Prefer the database’s documented CONCAT or `||` form for the query being written.

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Why does SQL string concatenation differ by database?

String concatenation joins text values into one string. SQL products expose it through operators, functions, and sometimes session settings with different type conversion and NULL rules.

The `||` operator is common in PostgreSQL and BigQuery. SQL Server’s CONCAT converts NULL arguments to empty strings, while MySQL’s CONCAT returns NULL if any argument is NULL. BigQuery’s CONCAT and operator documentation also define NULL propagation, so a cross-database query should not assume that a full name or key will survive missing parts unchanged.

Make an optional middle name explicit

SELECT
  CONCAT(
    first_name,
    ' ',
    COALESCE(middle_name, ''),
    ' ',
    last_name
  ) AS display_name
FROM people;

SQL String Concatenation Across Databases

Quick answer

FAQs

What operator concatenates strings in SQL?

Does CONCAT ignore NULL values?

Why use COALESCE with SQL concatenation?

Is + a safe string concatenation operator in SQL?

SQL LIKE Wildcards: %, _, and ESCAPE Explained

SQL CAST vs CONVERT: Safe Type Changes Across Databases

BigQuery UNNEST: Turn Arrays Into Rows Safely

Key takeaways

Why does SQL string concatenation differ by database?

How do you write portable concatenation?

Common mistakes to avoid

Official references

Quick answer

FAQs

What operator concatenates strings in SQL?

Does CONCAT ignore NULL values?

Why use COALESCE with SQL concatenation?

Is + a safe string concatenation operator in SQL?

Keep reading

SQL LIKE Wildcards: %, _, and ESCAPE Explained

SQL CAST vs CONVERT: Safe Type Changes Across Databases

BigQuery UNNEST: Turn Arrays Into Rows Safely

Key takeaways

Why does SQL string concatenation differ by database?

How do you write portable concatenation?

Common mistakes to avoid

Related SQL guides

Official references