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# PostgreSQL STRING_AGG Function

**Summary**: in this tutorial, you will learn how to use the PostgreSQL `STRING_AGG()` function to concatenate strings and place a separator between them.

## Introduction to PostgreSQL STRING_AGG() function

The PostgreSQL `STRING_AGG()` function is an aggregate function that concatenates a list of strings and places a separator between them. It does not add the separator at the end of the string.

The following shows the syntax of the `STRING_AGG()` function:

```sql
STRING_AGG ( expression, separator [order_by_clause] )
```

The `STRING_AGG()` function accepts two arguments and an optional `ORDER BY` clause.

- `expression` is any valid expression that can resolve to a character string. If you use other types than character string type, you need to explicitly [cast](../postgresql-tutorial/postgresql-cast) these values of that type to the character string type.
- `separator` is the separator for concatenated strings.

The `order_by_clause` is an optional clause that specifies the order of concatenated results. It has the following form:

```sql
ORDER BY expression1 {ASC | DESC}, [...]
```

The `STRING_AGG()` is similar to the [`ARRAY_AGG()`](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-array_agg) function except for the return type. The return value of the `STRING_AGG()` function is a string whereas the return value of the `ARRAY_AGG()` function is an [array](../postgresql-tutorial/postgresql-array).

Like other aggregate functions such as [`AVG()`](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-avg-function), [`COUNT()`](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-count-function), [`MAX()`](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-max-function), [`MIN()`](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-min-function), and [`SUM()`](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-sum-function), the `STRING_AGG()` function is often used with the [`GROUP BY`](../postgresql-tutorial/postgresql-group-by) clause.

## PostgreSQL STRING_AGG() function examples

We will use the `film`, `film_actor`, and `actor` tables from the [sample database](../postgresql-getting-started/postgresql-sample-database) for the demonstration:

### 1) Using PostgreSQL STRING_AGG() function to generate a list of comma-separated values

This example uses the `STRING_AGG()` function to return a list of actor's names for each film from the `film` table:

```sql
SELECT
    f.title,
    STRING_AGG (
	a.first_name || ' ' || a.last_name,
        ','
       ORDER BY
        a.first_name,
        a.last_name
    ) actors
FROM
    film f
INNER JOIN film_actor fa USING (film_id)
INNER JOIN actor a USING (actor_id)
GROUP BY
    f.title;
```

Here is the partial output:

```
            title            |                                                                                                   actors
-----------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Academy Dinosaur            | Christian Gable,Johnny Cage,Lucille Tracy,Mary Keitel,Mena Temple,Oprah Kilmer,Penelope Guiness,Rock Dukakis,Sandra Peck,Warren Nolte
 Ace Goldfinger              | Bob Fawcett,Chris Depp,Minnie Zellweger,Sean Guiness
 Adaptation Holes            | Bob Fawcett,Cameron Streep,Julianne Dench,Nick Wahlberg,Ray Johansson
...
```

### 2) Using the PostgreSQL STRING_AGG() function to generate a list of emails

The following example uses the `STRING_AGG()` function to build an email list for each country, with emails separated by semicolons:

```sql
SELECT
    country,
    STRING_AGG (email, ';') email_list
FROM
    customer
INNER JOIN address USING (address_id)
INNER JOIN city USING (city_id)
INNER JOIN country USING (country_id)
GROUP BY
    country
ORDER BY
    country;
```

The following picture shows the partial output:

![PostgreSQL STRING\_AGG function email list example](https://neon.com/postgresqltutorial/PostgreSQL-STRING_AGG-function-email-list-example.png)

## Summary

- Use the PostgreSQL `STRING_AGG()` function to concatenate strings and place a separator between them.

---

## Related docs (PostgreSQL Aggregate Functions)

- [ARRAY_AGG](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-array_agg)
- [AVG](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-avg-function)
- [BOOL_AND](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-bool_and)
- [BOOL_OR](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-bool_or)
- [COUNT](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-count-function)
- [MAX](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-max-function)
- [MIN](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-min-function)
- [SUM](https://neon.com/postgresql/postgresql-aggregate-functions/postgresql-sum-function)