mysql - 如何在 select 语句中连接两个可能包含 NULL 值的列？

Question

我试过:

SELECT CONCAT(col1, col2) AS NewCol FROM tableName

它仅在 col1 和 col2 不为空时有效，否则 NewCol 变为空，即使 col1 和 col2 之一不为空。我希望它显示任何可用的值。

Answer 1

使用CONCAT_WS .

SELECT CONCAT_WS('', col1, col2) AS NewCol FROM tableName

如果两个值都是null，它将返回一个空字符串。

文档:

CONCAT_WS(separator,str1,str2,...)

CONCAT_WS() stands for Concatenate With Separator and is a special form of CONCAT(). The first argument is the separator for the rest of the arguments. The separator is added between the strings to be concatenated. The separator can be a string, as can the rest of the arguments. If the separator is NULL, the result is NULL.