我正在尝试查询“标签”列中的所有唯一值。标签列中的每一行都可以包含多个值。因此，在不被迫进行规范化的情况下，如何查询多值列？
示例行：
Networking Professionalism Time Management Communication, Networking Career Management, Professionalism Networking Communication Attitude, Interpersonal Skills, Professionalism Business Protocol, Career Management, Communication, Leadership Business Protocol, Networking
如果最大元素数量是可预测的，则可以使用此方法（请注意，您需要使用UNION，而不是UNION ALL）
UNION
UNION ALL
Select DISTINCT thefield from thetable where Instr(thefield, ',') = 0 UNION Select Distinct Mid(thefield, 1, Instr(thefield, ',')) from thetable Where len(thefield) - len(replace(thefield,',','')) = 1 UNION Select Distinct Mid(thefield, Instr(thefield, ',')+1) from thetable Where len(thefield) - len(replace(thefield,',','')) = 1 UNION Select Distinct Mid(thefield, Instr(thefield, ',')+1, Instr(Instr(thefield, ',')+1,thefield, ',')) from thetable Where len(thefield) - len(replace(thefield,',','')) = 2 UNION Select Distinct Mid(thefield, Instr(Instr(thefield, ',')+1,thefield, ',')+1) from thetable Where len(thefield) - len(replace(thefield,',','')) = 2 --.. and so on (repeat last two Selects as many time as you wish, increasing the where condition by one for each pair)
看起来有些笨拙，但应该可以完成工作。未经测试，因此，在值之前或之后可能会出现一个逗号逗号
