資料結構
網路
RDBMS
作業系統
Java
MS Excel
iOS
HTML
CSS
Android
Python
C 程式設計
C++
C#
MongoDB
MySQL
Javascript
PHP
物理
化學
生物
數學
英語
經濟
心理學
社會科學
時尚研究
法律研究在一個 MySQL 查詢中實現多個 COUNT()
為此，使用 CASE 語句。首先，建立一個表 −
mysql> create table DemoTable -> ( -> LastName varchar(100) -> ); Query OK, 0 rows affected (0.60 sec)
使用 insert 命令在表中插入一些記錄 −
mysql> insert into DemoTable values('Smith');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values('Brown');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values('Brown');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('Smith');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('Taylor');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('Taylor');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Miller');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Miller');
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable values('Miller');
Query OK, 1 row affected (0.12 sec)使用 select 語句顯示錶中的所有記錄 −
mysql> select *from DemoTable;
輸出
這將產生以下輸出 −
+----------+ | LastName | +----------+ | Smith | | Brown | | Brown | | Smith | | Taylor | | Taylor | | Miller | | Miller | | Miller | +----------+ 9 rows in set (0.00 sec)
以下是查詢，在一個查詢中實現多個 COUNT() 方法 −
mysql> select COUNT(CASE WHEN LastName='Smith' THEN 1 END) AS TotalFrequency, -> COUNT(CASE WHEN LastName='Brown' THEN 1 END) AS TotalFrequency, -> COUNT(CASE WHEN LastName='Taylor' THEN 1 END) AS TotalFrequency, -> COUNT(CASE WHEN LastName='Miller' THEN 1 END) AS TotalFrequency -> from DemoTable;
輸出
這將產生以下輸出 −
+----------------+----------------+----------------+----------------+ | TotalFrequency | TotalFrequency | TotalFrequency | TotalFrequency | +----------------+----------------+----------------+----------------+ | 2 | 2 | 2 | 3 | +----------------+----------------+----------------+----------------+ 1 row in set (0.00 sec)
於以下日期更新： 30-6 月-2020
693 次瀏覽
廣告