What will MySQL return if we use NULL as parameter, one of the parameters, and delimiter in CONCAT_WS() function?

NULL as two parameters

If we use NULL as two parameters in CONCAT_WS() function, MySQL will return blank output.

Example

mysql> Select CONCAT_WS('',NULL,NULL);
+-------------------------+
| CONCAT_WS('',NULL,NULL) |
+-------------------------+
|                         |
+-------------------------+
1 row in set (0.00 sec)

NULL as one of the parameters

If we use NULL as one of the parameters in the CONCAT_WS() function, MySQL will return the value of the other parameter as output .

Example

mysql> Select CONCAT_WS('',NULL,'Delhi');
+----------------------------+
| CONCAT_WS('',NULL,'Delhi') |
+----------------------------+
| Delhi                      |
+----------------------------+
1 row in set (0.00 sec)

mysql> Select CONCAT_WS('','Ram',NULL);
+--------------------------+
| CONCAT_WS('','Ram',NULL) |
+--------------------------+
| Ram                      |
+--------------------------+
1 row in set (0.00 sec)

NULL at delimiter

If we use NULL at delimiter in CONCAT_WS() function, MySQL will return NULL as output.

Example

mysql> Select CONCAT_WS(NULL, 'NEW','DELHI');
+--------------------------------+
| CONCAT_WS(NULL, 'NEW','DELHI') |
+--------------------------------+
| NULL                           |
+--------------------------------+
1 row in set (0.00 sec)

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