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How do I create an indexes for "date"?
CentOS7, MongoDB server version: 3.4.2
db.animals.createIndex('date')
{
"ok" : 0,
"errmsg" : "The field 'key' must be an object, but got string",
"code" : 14,
"codeName" : "TypeMismatch"
}
db.animals.find({}, {date: 1}).limit(1)
{ "_id" : 3477, "date" : ISODate("2016-12-22T09:38:59Z") }
594
CREATE UNIQUE INDEX SyntaxON table_name (column1, column2, ...); Note: The syntax for creating indexes varies among different databases. Therefore: Check the syntax for creating indexes in your database.
1 Answer. If you have a dataframe named 'df' with DatetimeIndex, the following command will add a column labeled 'Timestamp' and the values corresponding to the values of the index: df['Timestamp'] = df. index.
Is it a good idea to have a index on the Timestamp column ? Yes, it is generally a good idea to have an index on a field used in a query criteria. This is really useful when there are a large number of documents (e.g., a million) in the collection. The index will be used to run the query fast.
If we want to create indexes for unique values in a column, we use the CREATE UNIQUE INDEX constraint. For example, -- create unique index CREATE UNIQUE INDEX college_index ON Colleges(college_code); Here, the SQL command creates a unique index named college_index on the Colleges table using the college_code column.
You can create simple index on key date using:
Ascending order: db.animals.createIndex({'date':1})
Descending order: db.animals.createIndex({'date':-1})
You may need to take a look at indexing doc before adding indexes
197
for single field you don't need to reverse the index as mongodb can use the index in either direction. It should only matter when you have a compound index and you have a sort going in different directions.
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