# 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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