[SQL] Index creation question for expression (col1 || '-' || col2)

[Ying Lu]

Greetings,

A question about creating index for the following expression.
CREATE INDEX idx_t1 ON test (col1 || '-' || col2);

May I know is it possible and how I may create index for the expression 
such as "col1 || '-' || col2" for a table please?

Thanks a lot,
Emi



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