concat

This function is used to concatenate arrays or strings.

If multiple arrays are used as the input, all elements in the arrays are connected to generate a new array.

concat(array<T> <a>, array<T> <b>[,...])

If multiple strings are used as the input, the strings are connected to generate a new string.

concat(string <str1>, string <str2>[,...])

Using arrays as the input

**Table 1** Parameters
Parameter	Mandatory	Type	Description
a, b	Yes	STRING	Array In array<T>, T indicates the data type of the elements in the array. The elements in the array can be of any type. The data types of elements in arrays a and b must be the same. If the values of the elements in an array are NULL, the elements are involved in the operation.

Using strings as the input

**Table 2** Parameters
Parameter	Mandatory	Type	Description
str1, str2	Yes	STRING	String If the value of the input parameter is of the BIGINT, DOUBLE, DECIMAL, or DATETIME type, the value is automatically converted to the STRING type for calculation. For other types of values, an error is reported.

The return value is of the ARRAY or STRING type.

If the return value is of the ARRAY type and any input array is NULL, NULL is returned.
If the return value is of the STRING type and there is no parameter or any parameter is NULL, NULL is returned.

Connect the array (1, 2) and array (2, -2). An example command is as follows:
The value [1, 2, 2, -2] is returned.
```
select concat(array(1, 2), array(2, -2));
```
Any array is NULL. An example command is as follows:
The value NULL is returned.
```
select concat(array(10, 20), null);
```
Connect strings ABC and DEF. An example command is as follows:
The value ABCDEF is returned.
```
select concat('ABC','DEF');
```
The input is empty. An example command is as follows:
The value NULL is returned.
```
select concat();
```
The value of any string is NULL. An example command is as follows:
The value NULL is returned.
```
select concat('abc', 'def', null);
```