Question

postgresql建了索引，查询用不上怎么回事

Answer 1

问题源自一个帅哥在建索引发生表锁的问题。先介绍一下Postgresql的建索引语法：
Version:9.1
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ name ] ON table [ USING method ]
( { column | ( expression ) } [ COLLATE collation ] [ opclass ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ WITH ( storage_parameter = value [, ... ] ) ]
[ TABLESPACE tablespace ]
[ WHERE predicate ]
这里不解释语法的诸多参数使用(排序，使用方法，填充因子等)，主要说一下concurrently的使用场景。