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select-mysql 嵌套查询，一个表的多个字段 作为另一个表的条件，若为空输出0，求高手
- WBOYOriginal
- 2016-06-06 09:34:351054browse
selectmysqlsql
SELECT daan
FROM 表A a，表B a
WHERE daan=b.选项1 or daan =b.选项2
问题来了
若 从表A 查 表B的选项，daan为空，怎么输出0
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