如何使用MySQL查询在列中查找特定ID的字符串计数？
为此，请在MySQL中使用CHAR_LENGTH()函数。让我们首先创建一个表-
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Subject longtext );
现在您可以使用insert命令在表中插入一些记录-
mysql> insert into DemoTable(Subject) values('MySQL,MongoDB');
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable(Subject) values('MySQL,MongoDB');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable(Subject) values('MongoDB');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable(Subject) values('MySQL');
Query OK, 1 row affected (0.15 sec)
Display all records from the table using select statement :
mysql> select *from DemoTable;输出结果
+----+---------------+ | Id | Subject | +----+---------------+ | 1 | MySQL,MongoDB | | 2 | MySQL,MongoDB | | 3 | MongoDB | | 4 | MySQL | +----+---------------+ 4 rows in set (0.00 sec)
以下是在列中使用特定ID的MySQL查询来查找字符串计数的查询。我们正在这里检查ID1-
mysql> select Id,char_length(Subject) - char_length(REPLACE((Subject), ',', ''))+1 AS FreqSubject from DemoTable WHERE char_length(Subject) > 0 AND Id = 1;
输出结果
+----+-------------+ | Id | FreqSubject | +----+-------------+ | 1 | 2 | +----+-------------+ 1 row in set (0.02 sec)