表达式

<field1_name> <mathematical_operator> <value>

age字段值加一

取集合中age字段，age值加1

> db.exec( "select age + 1 from foo.bar" )
{
}

比较表达式

<field1_name> <comparison_operator> <value> <> <field1_name> <comparison_operator> <value>

• age字段大于11

查询匹配age大于11的记录。

> db.exec( "select * from foo.bar where age > 11" )
{
  "_id": {
  "$oid": "5aa3330fdc5673331f000000"
  },
  "name": "Lucy",
}

• age字段大于等于11，且name为Harry

> db.exec( "select * from foo.bar where age >= 11 AND name = 'Harry'" )
{
  "_id": {
  "$oid": "5aa35dbedc5673331f000001"
  },
  "name": "Harry",
}