sql count distinct values

, as shown in result 1. Figure 1. Obviously, the result is 0 Therefore, when you specify Count (*), Count (1), or whatever Count ('anything '), the results will be the same, because these values are not NULL, as shown in 2. Figure 2. As long as a non-NULL expression is specified in

Count different values in a time span. The number of occurrences of the period. Here, I want to query the number of times that the periods field of each month has different values in one year. For example, in the-4 month, periods appears 3 times for 2 and 3 once for 3. The most important thing is periods. You don't know how many of them exist...

result is 0. So when you specify count (*) or COUNT (1) or count (' anything '), the result will be the same, because these values are not NULL, as shown in Figure 2. Figure 2. As long as you specify a non-null expression in count, the result is no different What abo

(*) FROMuser_operation_log Statistics origin This column value is not a NULL number:? 1 SELECTcount(origin) FROMuser_operation_log So we can use this feature to achieve the above requirements.First notation (implemented with count)? 12345 SELECTcount(origin = ‘iPhone‘ OR NULL) AS iPhone,count(origin = ‘Android‘ OR NULL) AS Android,

>>> Rdd = Sc.parallelize ([("a","1"), ("b", 1), ("a", 1), ("a", 1)])>>>rdd.distinct (). Countbykey (). Items () [('a', 2), ('b', 1)]or: fromoperatorImportaddRdd.distinct (). Map (lambda x: (x[0], 1)). Reducebykey (ADD)rdd.distinct (). Keys (). Map (Lambda x: (x, 1)). Reducebykey (ADD)distinct (numpartitions=none)Return a new rdd containing the distinct elements in this rdd.Sorted(SC. Parallelize([1123]).

Label:The format of a general SELECT statement is as follows: 1. Querying all columns of a specified table SELECT * from Table name [ where condition ] [group by Group column name ] [ having aggregate function ] [ORDER BY Sort Column name asc| DESC] Multiple tables can be written in the table name area 2. Query some columns of the specified table: Select {[DISTINCT] column name, column name,...} from table name [where condition ] [group by Group c

. First of all, naturally think of using the distinct function to weighSELECT DISTINCT ID, Description from BThe result is 1 records are not removed, because distinct is in multi-column, that is, must be ID and description all the same will be rejected.After searching the internet, it was said that using select *, COUNT