# Handling NULL
__*NULL Behavior*__
+ Passing **`NULL`** to the **`CONCAT()`** function causes it to return **`NULL`** 
+ **`CONCAT_WS()`** ignores NULL arguments
+ For example:
  + **`SELECT CONCAT('Welcome ', 'to ', NULL), CONCAT_WS(' ','Welcome','to', NULL);`**  
```
tidb> SELECT CONCAT('Welcome ', 'to ', NULL), CONCAT_WS(' ','Welcome','to' ,NULL);
+---------------------------------+------------------------------------+
| CONCAT('Welcome ', 'to ', NULL) | CONCAT_WS(' ','Welcome','to',NULL) |
+---------------------------------+------------------------------------+
| ~!@NULL@!~                            | Welcome to                         |
+---------------------------------+------------------------------------+
1 row in set (0.00 sec)
```

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