Support preliminary/tentative index use when planning LIKE with a non-literal argument (parameter, column reference, etc)

[mrotteveel]

Currently LIKE can only use parameter if it has a literal argument and it doesn't start with a wildcard. As soon as a parameter or column reference is used, an index can no longer be used.

I guess it could be possible to implement a way for LIKE to also use an index in those cases, conditionally on the actual value of the argument. That is, if the value doesn't start with a wildcard, it uses an index, and if it does start with a wildcard, a full scan is used.