Re: Proposal for col LIKE $1 with generic Plan

Thanks to the get_index_clause_from_support, we can use index for WHERE a like
'abc%' case. However this currently only works on custom plan. Think about the
case where the planning takes lots of time, custom plan will not give a good
result. so I want to see if we should support this for a generic plan as well.

The first step of this is we need to find an operator to present prefix is just
literal. which means '%' is just '%', not match any characters. After trying
'like' and '~' operator, I find none of them can be used. for example:

PREPARE s AS SELECT * FROM t WHERE a LIKE ('^' || $1);
EXECUTE s('%abc');

'%' is still a special character to match any characters.  So '~' is.  So I think

we need to define an new operator like text(a) ~^ text(b), which means a 

is prefixed with b literally. For example:

'abc' ~^ 'ab` -> true
'abc' ~^ 'ab%' -> false

so the above case can be written as:

PREPARE s AS SELECT * FROM t WHERE a ~^ $1;