DISTINCT: Return Distinct number of records from the column or distinct combinations of column values if multiple columns are specified. Generally speaking, the DISTINCT clause is a special case of the GROUP BY clause. You can use the count() function in a select statement with distinct on multiple columns to count the distinct rows. 这里说的双count(distinct)是指类似下面的语句 select day,count(distinct session_id),count(distinct user_id) from log a group by day; 如果要执行这样的语句，前提必须设置参数:set hive.groupby.... 同时有COUNT和GROUP BY的慢查询sql优化实例 SELECT DISTINCT TOP 10 City FROM Person.Address. COUNT: Returns either the number of non-NULL records for the specified columns, or the total number of records. Instead of doing all that work, we can compute the distincts in advance, which only needs one hash set. Table 'Address'. This new function of SQL Server 2019 provides an approximate distinct count of the rows. Example 1 : Suppose you have three variables, say, 'id', 'x' and 'y'. Let us start with the definitions of Count, Distinct and Null. Count(distinct CASE Date WHEN '01/02/2010' THEN Compte ELSE null END) AS [Comptes Unique Fév] Viewing 4 posts - 1 through 4 (of 4 total) You must be logged in to reply to this topic. There might be a slight difference in the SQL Count distinct and Approx_Count_distinct function output. Count distinct builds a hash set for each group — in this case, each dashboard_id — to keep track of which values have been seen in which buckets. SQL COUNT( ) with All In the following, we have discussed the usage of ALL clause with SQL COUNT() function to count only the non NULL value for the specified column within the argument. Here is an example: SELECT COUNT(*) FROM ( SELECT DISTINCT agent_code, ord_amount,cust_code FROM orders WHERE agent_code='A002'); Output: You may also use the COUNT SQL function for getting the number of records as using the DISTINCT clause. COUNT() function and SELECT with DISTINCT on multiple columns. COUNT CASE, COUNT DISTINCT 조건에 따른 카운트 및 중복을 제거한 카운트를 세보자 COUNT CASE (조건 카운트) 특정 조건에 해당하는 행의 카운트를 세보자 SELECT COUNT(CASE WHEN … The difference between DISTINCT clause and GROUP BY clause is that the GROUP BY clause sorts the result set whereas the DISTINCT clause does not.. Notice that MySQL 8.0 removed the implicit sorting for the GROUP BY clause. Table 'Worktable'. The difference between ‘*’(asterisk) and ALL are, '*' counts … It is frequently used with COUNT function to calculate number of unique cases. For the demo, I am using employee table that stores the information about the employees. You must have used DISTINCT keyword to remove duplicates. If you specify the asterisk character (*), then COUNT returns a count of all of the rows that matched the predicate, including duplicates and nulls, or a count in a given … The example of COUNT function with DISTINCT. See the snapshot of data below - You can replace SQL COUNT DISTINCT with the keyword Approx_Count_distinct to use this function from SQL Server 2019. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. You can count all rows (using ALL), or distinct values of the expression (using DISTINCT). Good! Now, in certain situations you may also want to include DISTINCT in your CASE WHEN statements with COUNT.Take a look: SELECT COUNT(DISTINCT CASE WHEN pay_date BETWEEN '2015-06-01' AND '2015-06-05' THEN candidate_id END) AS accepted_student, COUNT(DISTINCT CASE WHEN pay_date = '2015-06-06' THEN candidate_id END) AS conditionally_accepted_student, COUNT(DISTINCT CASE … The function returns only count for the rows returned after DISTINCT clause. Therefore, if you use MySQL 8.0+, you will find that the result set of the above query … You need to calculate number of distinct "y" values when x is less than 30. 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