Difference between revisions of "MongoDB QueryData"
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This is akin to a SQL query: | This is akin to a SQL query: | ||
| + | <pre font="blue"> | ||
SELECT * FROM Emp WHERE deptno=20 AND empno = 7902 | SELECT * FROM Emp WHERE deptno=20 AND empno = 7902 | ||
| + | </pre> | ||
However, could you just query using the empno? | However, could you just query using the empno? | ||
Revision as of 21:05, 18 October 2016
Show all data so far:
db.deptCollection.find()
Comes back messy, can make it better:
db.deptCollection.find().pretty()
Or just find one document:
db.deptCollection.find({"deptno":10}).pretty()
Finding an employee means using the array name too:
db.deptCollection.find({"employees.empno":7902}).pretty()
However, does mean you get back all the employees!
Since version 2.2 MongoDB's new $elemMatch can avoid this:
db.deptCollection.find({"deptno":20},
{ _id: 0, employees: {$elemMatch: {empno: 7902}}}).pretty()
$elemMatch limits the contents of the employees array to contain only the first element matching the $elemMatch condition.
_id is a unique value automatically generated by MongoDB (like a Primary Key). To see it:
db.deptCollection.find({"deptno":20},
{ employees: {$elemMatch: {empno: 7902}}}).pretty()
This is akin to a SQL query:
SELECT * FROM Emp WHERE deptno=20 AND empno = 7902
However, could you just query using the empno?
