# Concatenate strings and arrays
<a name="concatenating-strings-and-arrays"></a>

Concatenating strings and concatenating arrays use similar techniques.

## Concatenate strings
<a name="concatenating-strings"></a>

To concatenate two strings, you can use the double pipe `||` operator, as in the following example.

```
SELECT 'This' || ' is' || ' a' || ' test.' AS Concatenated_String
```

This query returns:


****  

| \$1 | Concatenated\$1String | 
| --- | --- | 
| 1 |  `This is a test.`  | 

You can use the `concat()` function to achieve the same result.

```
SELECT concat('This', ' is', ' a', ' test.') AS Concatenated_String
```

This query returns:


****  

| \$1 | Concatenated\$1String | 
| --- | --- | 
| 1 |  `This is a test.`  | 

You can use the `concat_ws()` function to concatenate strings with the separator specified in the first argument.

```
SELECT concat_ws(' ', 'This', 'is', 'a', 'test.') as Concatenated_String
```

This query returns:


****  

| \$1 | Concatenated\$1String | 
| --- | --- | 
| 1 |  `This is a test.`  | 

To concatenate two columns of the string data type using a dot, reference the two columns using double quotes, and enclose the dot in single quotes as a hard-coded string. If a column is not of the string data type, you can use `CAST("column_name" as VARCHAR)` to cast the column first.

```
SELECT "col1" || '.' || "col2" as Concatenated_String
FROM my_table
```

This query returns:


****  

| \$1 | Concatenated\$1String | 
| --- | --- | 
| 1 |  `col1_string_value.col2_string_value`  | 

## Concatenate arrays
<a name="concatenating-arrays"></a>

You can use the same techniques to concatenate arrays.

To concatenate multiple arrays, use the double pipe `||` operator.

```
SELECT ARRAY [4,5] || ARRAY[ ARRAY[1,2], ARRAY[3,4] ] AS items
```

This query returns:


****  

| \$1 | items | 
| --- | --- | 
| 1 |  `[[4, 5], [1, 2], [3, 4]]`  | 

To combine multiple arrays into a single array, use the double pipe operator or the `concat()` function.

```
WITH
dataset AS (
  SELECT
    ARRAY ['Hello', 'Amazon', 'Athena'] AS words,
    ARRAY ['Hi', 'Alexa'] AS alexa
)
SELECT concat(words, alexa) AS welcome_msg
FROM dataset
```

This query returns:


****  

| \$1 | welcome\$1msg | 
| --- | --- | 
| 1 |  `[Hello, Amazon, Athena, Hi, Alexa]`  | 

For more information about `concat()` other string functions, see [String functions and operators](https://trino.io/docs/current/functions/string.html) in the Trino documentation.