Re:Re: Different execution plan between PostgreSQL 8.2 and 12.5

Dear Adrian,

I appreciate your reply. Your reply gave me a new idea, 

it should not be the problem that the lower() function causes the unique index to fail. 

I checked the postgresql.conf file and found that shared_buffers, work_mem and maintenance_work_mem are default value, 

but in the postgresql.conf file of PostgreSQL 8.4, the value of these parameters are very large. 

When I changed the value of these parameters to a larger value, the problem solved.