5 rowsinset(0.02 sec) group by的使用对于基础去重来说, group by 的使用和distinct类似:单列去重 语法: SELECT columns FROM table_name WHERE where_conditions GROUP BY columns; 执行: mysql> select age from student group by age; +---+ | age | +---+ | 10 | | 12 | | 11 | | NULL |...
ToTable() has an overload which lets you specify whether or not to return only distinct values, and a params string[] argument to specify which columns you want in the new table. If you specify true as the first argument, only rows unique within the columns that you specify in the para...
Select Distinct Rows from DataTable ' True=distinct Dim table As DataTable = Me.SP3DPIA2014R1DataSet.SP3DPIA.AsDataView.ToTable(True, "ShortName") Sp3dpiareflection.sln
DISTINCT可选,显示结果是否去重 使用表达式堆查询的列进行运算 SELECT *|{column1 | expression, column2 | expression, ...} FROM tablename 使用as语句 SELECT columnname as 别名 from 表名 WHERE子句 ORDER BY子句 SELECT column1,column2,column3.. FROM table; order by column asc|desc, ... Order b...
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使用DISTINCT关键字:在SELECT语句中使用DISTINCT关键字可以去除重复的行,只返回唯一的行。例如,SELECT DISTINCT column_name FROM table_name WHERE condition; 使用聚合函数:聚合函数如COUNT、SUM、AVG等可以对查询结果进行汇总计算,从而返回唯一的行。例如,SELECT COUNT(column_name) FROM table_name WHERE condition; ...
SELECT DISTINCT Lastname ,FirstName ,MiddleName FROM Person.Person; Notice the first few rows in the result set in Figure 5. Figure 5. Duplicates in the first 2 columns using DISTINCT in a 3-column SELECT The first few rows are all unique. The DISTINCT keyword made sure that theMiddlenam...
6 rows in set (0.00 sec) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 查询指定数据 ; select * from 表名 where 字段名 = ’数据’; select * from 表名 where 字段名 比较运算符 数据; (后附比较运算符表) 查询表student里列num为901的学生信息: ...
SELECT first_name FROM contacts ORDER BY first_name; Code language: SQL (Structured Query Language) (sql) The query returned 319 rows, indicating that the contacts table has 319 rows. To get unique contact first names, you add the DISTINCT keyword to the above SELECT statement as follows: ...
SELECT DISTINCT accountid FROM table; COUNT DISTINCT子句 命令简介 COUNT DISTINCT支持计算去重之后的某一个column的个数,对于该列中出现多次的值只会被计算一次,和COUNT的计算类似,如果该列包含NULL值,它将不会计算在内。 语法说明 精确计算的语法示例如下: SELECT c1, COUNT(DISTINCT c2) FROM table GROUP BY...