# SERIAL()

## Function description

The SERIAL() function is used to serialize a connection string, combining a single or multiple columns/values into a binary format, with the return type `VARCHAR`. It is similar to [`CONCAT()`](../../../Functions-and-Operators/String/concat.md), but in `CONCAT()`, the type information of the value cannot be captured. Generally used with the [`SERIAL_EXTRACT()`](../../../Functions-and-Operators/Other/serial_extract.md) function.

If any of the parameters in `SERIAL()` is NULL, NULL is returned. To process NULL values, use [`SERIAL_FULL()`](serial_full.md).

## Function Syntax

```text
> SERIAL(para)
```

## Parameter definition

| Parameters | Description |
| ---- | ---- |
| para | Column/value to serialize |

## Example

```text
create table t1(a varchar(3), b int);
insert into t1 values("ABC",1);
insert into t1 values("DEF",NULL);

mysql> select serial(a,b) from t1;--The query returns the result of serialization of column a and column b. When there is a NULL value, the output is NULL
+-------------------+
| serial(a, b) |
+-------------------+
| FABC : |
| NULL |
+-------------------+
2 rows in set (0.00 sec)

mysql> select serial(a,'hello') from t1;--Query returns the result of a column and value hello combination serialization
+------------------------+
| serial(a, hello) |
+------------------------+
| FABC Fhello |
| FDEF Fhello |
+------------------------+
2 rows in set (0.00 sec)
```