問題描述

SELECT ifnull(字段A,字段B) FROM tbl ....

這里我想的是如果字段A為空就取字段B的值，可以這樣寫似乎不對，求教~

(SELECT (CASE 字段A WHEN NOT NULL THEN 字段A ELSE 字段B END) FROM tbl WHERE tb1.id=tb2.id) as name

這是完整語句，最終name無法實現我想要的效果

問題解答

用 COALESCE(A,B)SELECT COALESCE(A,B) FROM tbl

select (case A when not null then A else B end) as result from tbl

去掉了is可以了

SELECT CASE WHEN BIRTHDAY IS NULL THEN PASSWORD ELSE BIRTHDAY ENDFROM table_name;

(SELECT (CASE 字段A WHEN IS NOT NULL THEN 字段A ELSE 字段B END) FROM tbl WHERE tb1.id=tb2.id) as name

IS NOT NULL