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In the past two blogs, the topic mainly focus on the high query operation of mongodb.In this blog, we simply study the regex expression in the mongdb.  MongoDB also support the regex query. For example

The expression is also able to combination with other expression.

Notes: /^a/; /^a.*/; /^a.*$/ have the same result, however the later two have less efficiency than the first one. Because the later will scan all the things, but the first only scan the first character. 

The item:

-i : ignore the upper or low case 

-m: the begin '^' and end'$' do work on every new line;

-x: ignore the blank character

-s:  since 1.9 version, adding it could make '.' reprent all the character. 

for example:

/a.*b/ does not matches "apple\nbanana" but /a.*b/s does.