Microsoft Access 2003 SQL问题

我需要在Microsoft Access中合并几个具有不同结构的表

例如，我有一个表：

table1 (column_a,column_b,column_c),
table2 (column_a,column_c),
table3 (column_d)

SQL如下所示：

SELECT table1 column_a,column_b,column_c, Null as column_d FROM Table1
UNION
SELECT table2 column_a,Null as column_b, column_c, Null as column_d FROM Table2
UNION
SELECT table3 column_a, Null as column_b, Null as column_c, Null as column_d 
FROM Table3;

但有时MS Access会显示有关不兼容类型的错误消息

我认为这是因为在一个SELECT中具有空值的生成列的类型与另一个SELECT中相应的非自动生成列的类型不兼容

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有没有办法用null指定自动生成列的类型？

用空字符串替换null怎么样

e、 g

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你为什么需要工会？如果不是数据按摩/导入操作，则看起来像是架构问题。

SELECT col_a, col_b,       col_c,       '' as col_d FROM Table1
UNION
SELECT col_a, '' as col_b, col_c,       '' as col_d FROM Table2
UNION
SELECT col_a, '' as col_b, '' as col_c, '' as col_d FROM Table3;