SELECT DISTINCT 列名 FROM 表名; 在这个查询中,列名是要选择非重复值的列的名称,表名是要查询的表的名称。 优势: 简单易用:使用DISTINCT关键字可以轻松选择非重复的列值,无需复杂的逻辑或编程。 提高查询效率:通过去除重复的行,可以减少查询结果的大小,从而提高查询的性能和效率。 应用场景: 数据去重:当需要从...
WHERE agent_code='A002': This line specifies a condition for filtering the results. It filters the results to only include rows where the value in the 'agent_code' column is 'A002'. This condition acts as a filter, allowing only rows with 'A002' as the agent code to be included in t...
(c1 INT PRIMARY KEY, c2 INT) PARTITION BY KEY(c1) PARTITIONS 4; Query OK, 0 rows affected obclient> INSERT INTO t3 VALUES(5,5),(1,1),(2,2),(3,3); Query OK, 4 rows affected Records: 4 Duplicates: 0 Warnings: 0 obclient> SELECT * FROM t3; +---+---+ | c1 | c2 | ...
-- select all countries from the Customers tableSELECTcountryFROMCustomers; This SQL command will return all country entries, including duplicates, from theCustomerstable. To learn more, visitSQL SELECT. Write an SQL query to filter out all the duplicate entries. Suppose you have a table namedLis...
SELECT语句中的算术表达式和空值 首先介绍显示表结构的命令 DESCRIBEcommand 描述命令:显示表结构 isplaying the Table Structure You can display the structure of a table by using the DESCRIBE command. The command displays the column names and the data types, and it shows you whether a column must cont...
简单地使用.drop_duplicates()获取不同的值: # SQL SELECT DISTINCT column_a FROM table_df # Pandas table_df['column_a'].drop_duplicates() SELECT a as b 如果你想重命名一个列,使用.rename(): # SQL SELECT column_a as Apple, column_b as Banana FROM table_df # Pandas table_df[['column...
SELECT Company FROM Cars; Here is the result: Company Toyota Toyota Honda Chevrolet Ford BMW Audi As you can see in the result above we have two entries for Toyota because in our table cars Toyota had two different models for that company. Sometimes you might want to remove duplicates like...
GROUP BY 函数就是 SQL 中用来实现分组的函数,其用于结合聚合函数,能根据给定数据列的每个成员对查询结果进行分组统计,最终得到一个分组汇总表。 语法: SELECT`column_name`, aggregate_function(`column_name`)FROM`table_name`WHERE`column_name`operatorvalueGROUPBY`column_name`; ...
02 sec) -- 4、当创建了联合索引之后再次使用age,phone进行排序 mysql> explain select id,age,phone from tb_user order by age , phone; +---+---+---+---+---+---+---+---+---+---+---+---+ | id | select_type | table | partitions | type | possible_keys ...
USEAdventureWorks2022; GOSELECTName, ProductNumber, ListPriceASPriceFROMProduction.ProductWHEREProductLine ='R'ANDDaysToManufacture <4ORDERBYNameASC; GO B. Use SELECT with column headings and calculations The following examples return all rows from theProducttable. The first example returns total sales...