sql count distinct values

heavy field, can be a single field name, can also be nested field names, query is the search criteria, can be empty; Example: Db.collection.distinct ("user", {"age": {$gt: 28}});//For querying different user names of age older than 28 years In addition to the above usage, you can use one of the following methods: Db.runcommand ({"distinct": "CollectionName", "Key": "Distinctfied", "Query": CollectionName: Go to the collection name of the statis

How to Use distinct to query multiple unique record values in mysql How to Use distinct to query multiple unique record values in mysql When using mysql, you sometimes need to query records with unique fields. Although mysql provides the keyword distinct to filter out redun

When MySQL is used to query multiple non-repeated record values using distinct, it is sometimes necessary to query records with no repeated fields, although mysql provides the keyword distinct to filter out redundant duplicate records and retain only one record, it is often used to return the number of records that do not repeat, rather than returning all

When using mysql, you sometimes need to query records with unique fields. Although mysql provides the keyword distinct to filter out redundant duplicate records, only one record is retained, but it is often used to return the number of records that do not repeat, instead of returning all values that do not record the record. The reason is that distinct can only r

When using MySQL, there are times when you need to query for records that are not duplicated in a field, although MySQL provides a distinct keyword to filter out excess duplicates, but it often only uses it to return the number of records that are not duplicates, rather than using it to return all values that are not logged. The reason for this is that distinct c

higher than count (COL), so do not use count (col) when you can use COUNT (*). the execution efficiency of count(COL) is higher than the count (distinct col), but this conclusion is not very significant, and both methods are als

-1872672 to 71-3249712 to 45-1867722-51-5454September 724-80-9391756-30-7391807-91-6654.846 to 92-7186899 to 46-2035998 to 72-3567 (19 row (s) affected) The output of statements that involve distinct depends on the column sorting rule or the expression that uses distinct. For more information about the effects of different sorting rules, see basic knowledge of SQL