The Ultimate Guide to High Availability with MariaDB

COALESCE

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语法:

COALESCE(value,...)

说明:

返回结果中第一个非空的值，如果结果集中都不为空，则返回null。最后一个参数必须赋值。

例子:

MariaDB [(none)]> SELECT COALESCE(NULL,1);
+------------------+
| COALESCE(NULL,1) |
+------------------+
|                1 |
+------------------+
1 row in set (0.00 sec)

MariaDB [(none)]> SELECT COALESCE(NULL,NULL,NULL);
+--------------------------+
| COALESCE(NULL,NULL,NULL) |
+--------------------------+
|                     NULL |
+--------------------------+
1 row in set (0.00 sec)

MariaDB [(none)]>

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