The predicates in the query in Listing 7 are weakly selective so that a full table scan of the PDBXML table is required.

清单7中查询的谓词选择性较弱，因此需要对pdbxml表进行全表扫描。

youdao

That is, over the past generation the most selective schools in the country got into the habit of listing a high sticker price and then discounting that price as needed in order to fill a class.

FORBES