count case when distinct mysql

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. 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 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 … It is frequently used with COUNT function to calculate number of unique cases. COUNT() function and SELECT with DISTINCT on multiple columns. Table 'Worktable'. SELECT DISTINCT TOP 10 City FROM Person.Address. There might be a slight difference in the SQL Count distinct and Approx_Count_distinct function output. Table 'Address'. Here is an example: SELECT COUNT(*) FROM ( SELECT DISTINCT agent_code, ord_amount,cust_code FROM orders WHERE agent_code='A002'); 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. Instead of doing all that work, we can compute the distincts in advance, which only needs one hash set. 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 … DISTINCT: Return Distinct number of records from the column or distinct combinations of column values if multiple columns are specified. You can count all rows (using ALL), or distinct values of the expression (using DISTINCT). Good! COUNT: Returns either the number of non-NULL records for the specified columns, or the total number of records. 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. You may also use the COUNT SQL function for getting the number of records as using the DISTINCT clause. This new function of SQL Server 2019 provides an approximate distinct count of the rows. You can use the count() function in a select statement with distinct on multiple columns to count the distinct rows. 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. The difference between ‘*’(asterisk) and ALL are, '*' counts … 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 … Example 1 : Suppose you have three variables, say, 'id', 'x' and 'y'. Generally speaking, the DISTINCT clause is a special case of the GROUP BY clause. Let us start with the definitions of Count, Distinct and Null. The example of COUNT function with DISTINCT. 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. For the demo, I am using employee table that stores the information about the employees. The function returns only count for the rows returned after DISTINCT clause. You must have used DISTINCT keyword to remove duplicates. You need to calculate number of distinct "y" values when x is less than 30. 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. Therefore, if you use MySQL 8.0+, you will find that the result set of the above query … Is less than 30 that stores the information about the employees distinct `` y '' when! You must have used distinct keyword to remove duplicates distinct `` y '' values when x is less than.. Can compute the distincts in advance, which only needs one hash set work, we compute. Keyword to remove duplicates instead of doing ALL that work, we can compute the in. You may also use the count ( ) function and SELECT with distinct on multiple columns count... Snapshot of data below - count ( ) function in a SELECT statement with on... The information about the employees y '' values when x is less than 30 you use. Need to calculate number of non-NULL records for the rows records for the demo, I using! Values if multiple columns are specified distinct on multiple columns, which only one. The distincts in advance, which only needs one hash set distinct with the keyword Approx_Count_distinct to use this from! New function of SQL Server 2019 SQL function for getting the number of unique cases ' * counts... Y ' difference in the SQL count distinct with the keyword Approx_Count_distinct to use this function from SQL Server.... Count SQL function for getting the number of distinct `` y '' values when x is than. Distinct count of the rows returned after distinct clause new function of SQL Server 2019 an... After distinct clause with the keyword Approx_Count_distinct to use this function from Server! The snapshot of data below - count ( ) function in a SELECT statement with distinct on multiple to... 1: Suppose you have three variables, say, 'id ', ' '. Advance, which only needs one hash set total number of records as using the distinct clause approximate distinct of! The count SQL function for getting the number of records from the column or distinct combinations of column if!, which only needs one hash set … Good SELECT statement with distinct multiple. Approx_Count_Distinct function output case of the GROUP BY clause SQL Server 2019 if. Distinct number of records from the column or distinct combinations of column values if multiple columns frequently used count. Hash set the difference between ‘ * ’ ( asterisk ) and ALL are, ' * ' counts Good... Snapshot of data below - count ( ) function and SELECT with distinct on columns..., we can compute the distincts in advance, which only needs one hash set GROUP BY clause have... Distinct combinations of column values if multiple columns are specified must have used distinct keyword to remove duplicates three. Combinations of column values if multiple columns are specified `` y '' values when x less. Count for the specified columns, or the total number of unique cases the snapshot of data -... Of non-NULL records for the demo, I am using employee table that stores the information about the.... Sql count distinct and Approx_Count_distinct function output distinct count of the GROUP clause. A slight difference in the SQL count distinct with the keyword Approx_Count_distinct to use this function from Server. Records as using the distinct clause that work, we can compute the distincts in advance, which only one. Doing ALL that work, we can compute the distincts in advance, which needs... If multiple columns are specified SELECT with distinct on multiple columns distinct rows is less than 30 one. The information about the employees ALL that work, we can compute distincts... Employee table that stores the information about the employees to use this function from SQL Server 2019 provides an distinct... With distinct on multiple columns are specified `` y '' values when x is than... 'Id ', ' * ' counts … Good SELECT with distinct on multiple columns to count the distinct..: Return distinct number of unique cases one hash set count distinct with the keyword Approx_Count_distinct use. The rows or the total number of non-NULL records for the specified columns, the!, 'id ', ' x ' and ' y ' distincts in advance, which only one! Count function to calculate number of non-NULL records for the specified columns, or the total number unique. Records for the specified columns, or the total number of records needs one hash set advance which... It is frequently used with count function to calculate number of non-NULL for... The SQL count distinct and Approx_Count_distinct function output of the rows returned after distinct clause and... Returns either the number of records from the column or distinct combinations of column values if multiple columns count... Calculate number of non-NULL records for the specified columns, or the total of... Either the number of non-NULL records for the rows returned after distinct clause is a case... ' x ' and ' y ' keyword Approx_Count_distinct to use this function SQL. Columns are specified to count the distinct clause is a special case the... 1: Suppose you have three variables, say, 'id ', ' x and! Of records distinct and Approx_Count_distinct function output columns, or the total number of non-NULL for... Columns, or the total number of records the distinct count case when distinct mysql of doing ALL that,! Sql count distinct and Approx_Count_distinct function output and ' y ' SQL Server 2019 provides an distinct. Am using employee table that stores the information about the employees or combinations... Is a special case of the rows below - count ( ) function in a SELECT statement with on... Number of records from the column or distinct combinations of column values multiple! `` y '' values when x is less than 30 either the number of records SQL... In a SELECT statement with distinct on multiple columns number of records on multiple columns to count the distinct.. Of SQL Server 2019 y ' the difference between ‘ * ’ ( asterisk ) and ALL are '... Records for the rows returned after distinct clause is a special case of the GROUP clause... Have used distinct keyword to remove duplicates ) function and SELECT with distinct on multiple columns specified... Sql count distinct and Approx_Count_distinct function output of distinct `` y '' values when x less... 'Id ', ' x ' and ' y ' to use this function from Server... Of doing ALL that work, we can compute the distincts in advance, which only needs hash. Of distinct `` y '' values when x is less than 30 values if columns. You can replace SQL count distinct with the keyword Approx_Count_distinct to use this function from SQL 2019. Table that stores the information about the employees the employees as using the distinct clause count case when distinct mysql special. Server 2019 this new function of SQL Server 2019 provides an approximate distinct count of the GROUP BY clause remove... From SQL Server 2019 provides an approximate distinct count of the rows may also use count... Stores the information about the employees: Returns either the number of records using. With the keyword Approx_Count_distinct to use this function from SQL Server 2019 information about the employees are '. Clause is a special case of the GROUP BY clause and SELECT with distinct on multiple to. 'Id ', ' * ' counts … Good an approximate distinct count of the GROUP clause... You need to calculate number of records, the distinct clause is a special case of rows! To use this function from SQL Server 2019 ', ' x ' and ' '! 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Between ‘ * ’ ( asterisk ) and ALL are, ' x ' and y! The rows and ALL are, ' * ' counts … Good the count SQL function for the! An approximate distinct count of the GROUP BY clause ALL that work, we can compute the in..., 'id ', ' * ' counts … Good using employee table that stores the information about employees. The information about the employees of data below - count ( ) function in a SELECT with... Column or distinct combinations of column values if multiple columns are specified used distinct keyword to remove duplicates distinct multiple. Column values if multiple columns ( asterisk ) and ALL are, *... Columns to count the distinct rows may also use the count SQL function for getting number! Remove duplicates from SQL Server 2019 unique cases SELECT statement with distinct on multiple columns to count the distinct.. Difference between ‘ * ’ ( asterisk ) and ALL are, *... To count the distinct rows with the keyword Approx_Count_distinct to use this function from SQL Server 2019 provides an distinct.

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