# CONCAT function
<a name="CONCAT"></a>

The CONCAT function concatenates two expressions and returns the resulting expression. To concatenate more than two expressions, use nested CONCAT functions. The concatenation operator (`||`) between two expressions produces the same results as the CONCAT function. 

**Note**  
For both the CONCAT function and the concatenation operator, if one or both expressions is null, the result of the concatenation is null. 

## Syntax
<a name="CONCAT-synopsis"></a>

```
CONCAT ( expression1, expression2 )
```

## Arguments
<a name="CONCAT-arguments"></a>

 *expression1*, *expression2*   
Both arguments can be a fixed-length character string, a variable-length character string, a binary expression, or an expression that evaluates to one of these inputs. 

## Return type
<a name="CONCAT-return-type"></a>

 CONCAT returns an expression. The data type of the expression is the same type as the input arguments. 

If the input expressions are of different types, AWS Clean Rooms tries to implicitly type casts one of the expressions. If values can't be cast, an error is returned.

## Examples
<a name="CONCAT-examples"></a>

The following example concatenates two character literals: 

```
select concat('December 25, ', '2008');

concat
-------------------
December 25, 2008
(1 row)
```

The following query, using the `||` operator instead of CONCAT, produces the same result: 

```
select 'December 25, '||'2008';

concat
-------------------
December 25, 2008
(1 row)
```

The following example uses two CONCAT functions to concatenate three character strings: 

```
select concat('Thursday, ', concat('December 25, ', '2008'));

concat
-----------------------------
Thursday, December 25, 2008
(1 row)
```

To concatenate columns that might contain nulls, use the [NVL and COALESCE functions](NVL_function.md). The following example uses NVL to return a 0 whenever NULL is encountered. 

```
select concat(venuename, concat(' seats ', nvl(venueseats, 0))) as seating
from venue where venuestate = 'NV' or venuestate = 'NC'
order by 1
limit 5;

seating                            
-----------------------------------
Ballys Hotel seats 0               
Bank of America Stadium seats 73298
Bellagio Hotel seats 0             
Caesars Palace seats 0             
Harrahs Hotel seats 0              
(5 rows)
```

The following query concatenates CITY and STATE values from the VENUE table: 

```
select concat(venuecity, venuestate)
from venue
where venueseats > 75000
order by venueseats;

concat
-------------------
DenverCO
Kansas CityMO
East RutherfordNJ
LandoverMD
(4 rows)
```

The following query uses nested CONCAT functions. The query concatenates CITY and STATE values from the VENUE table but delimits the resulting string with a comma and a space: 

```
select concat(concat(venuecity,', '),venuestate)
from venue
where venueseats > 75000
order by venueseats;

concat
---------------------
Denver, CO
Kansas City, MO
East Rutherford, NJ
Landover, MD
(4 rows)
```