("Col2", GetType(String)) newTable.Columns.Add(newColumn) ' Assign the table to the new data set newDataset.Tables.Add(newTable) ' Query the original data table returnung the columns Col1 and Col2, distinct collection Dim results = (From row In dataset.Tables(0).AsEnumerable() Select...
1、使用distinct去重 distinct用来查询不重复记录的条数,用count(distinct id)来返回不重复字段的条数。用法注意: distinct【查询字段】,必须放在要查询字段的开头,即放在第一个参数; 只能在SELECT 语句中使用,不能在 INSERT, DELETE, UPDATE 中使用; DISTINCT 表示对后面的所有参数的拼接取不重复的记录,即查出的参...
COUNT() function and SELECT with DISTINCT on multiple columns You can use the count() function in a select statement with distinct on multiple columns to count the distinct rows. Here is an example: SELECTCOUNT(*)-- Count the number of rows in the result setFROM(SELECTDISTINCTagent_code,or...
Re: Select count distinct multiple christian dickman October 13, 2006 04:34PM Re: Select count distinct multiple Marc Ayres October 16, 2006 07:39AM Re: Select count distinct multiple Marc Ayres October 16, 2006 12:40PM Sorry, you can't reply to this topic. It has been closed. ...
I've also run across this bug; in my case the unique index had a third column, and I noticed that the result of count distinct was the number of distinct rows for the first two columns. In other words, SELECT COUNT(DISTINCT a), COUNT(DISTINCT b) was equivalent to SELECT COUNT(DISTINC...
select DISTINCT age from p_user ORDER BY age asc; ② 按照年龄分组并count select *, COUNT(*) from p_user GROUP BY age; count( ):里面可以使用两种参数:*代表统计记录,字段名代表统计对应的字段(NULL不统计)。 count()是分组之后统计每组的记录数,单独执行count查询只会返回一行结果。
select DISTINCT NAME,age from p_user_2 1. 【2】字段别名 多表操作时可能会有字段名字重复,此时可重命名。 示例如下: select NAME [as] '用户名',age [as] '年龄' from p_user_2; -- as可缺省 1. 2. 3. 【3】数据源 数据源即数据的来源,关系型数据库数据来源为数据表。本质上只要保证数据类似...
Changing the category (not specific to a storage engine). COUNT() disposes of NULLs, but whether it should dispose of them in multi-column cases where only some of the columns are NULL is arguable. ie: I think that "2" is the logical return value for: SELECT COUNT(DISTINCT name, age...
If you useGROUP BY, output rows are sorted according to theGROUP BYcolumns as if you had anORDER BYfor the same columns. To avoid the overhead of sorting thatGROUP BYproduces, addORDER BY NULL: SELECTa,COUNT(b)FROMtest_tableGROUPBYaORDERBYNULL; ...
answer, however, youCASTyour 2 date columns to adatein yourSELECTbutnotin theGROUP BY. If those columns are a date and time value, then you're not grouping on the same values you have in yourSELECTand you will get a row for each distinct dateandtime on those columns, not just the ...