MySQL Operators API Reference

`SELECT`

5 methods

SELECT 语句中可用的子句。

{ $match: <query> }

从表中读取行，可选按布尔条件过滤。

Name	Type	Description
query	object	Selector document.

Stage

mongodb

{ $match: { status: 'active', age: { $gte: 18 } } }

{ $group: { _id: <expr>, <field>: { <accumulator>: <expr> } } }

基于连接谓词组合两个表的行；支持 INNER、LEFT、RIGHT、FULL。

Name	Type	Description
_id	expression	Group key expression; null groups all documents.
accumulator	string	$sum, $avg, $max, $min, $push, $addToSet, etc.

Stage

mongodb

{ $group: { _id: '$dept', avgSalary: { $avg: '$salary' } } }

{ $project: <specification> }

按列出的列分组行并应用聚合函数，用 HAVING 过滤分组。

Name	Type	Description
specification	object	Field inclusion (1), exclusion (0) or expression.

Stage

mongodb

{ $project: { name: 1, age: 1, _id: 0 } }

{ $lookup: { from, localField, foreignField, as } }

按给定列排序结果集并限制返回行数。

Name	Type	Description
from	string	Foreign collection name.
localField	string	Field from the input documents.
foreignField	string	Field from the foreign collection documents.
as	string	Output array field name.

Stage

mongodb

{ $lookup: { from: 'orders', localField: '_id', foreignField: 'userId', as: 'orders' } }

{ $sort: { <field>: 1 | -1 } }

Aggregation stage that sorts documents by the given fields; 1 ascending, -1 descending.

Name	Type	Description
field	string	Field path to sort by.

Stage

mongodb

{ $sort: { createdAt: -1 } }