如何使用 MySQL 查詢來尋找列中特定 id 的字串計數？

為此，請使用 MySQL 中的 CHAR_LENGTH() 函數。讓我們先建立一個表-

mysql> create table DemoTable
   (
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   Subject longtext
   );
Query OK, 0 rows affected (1.17 sec)

現在您可以使用插入命令在表中插入一些記錄-

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;

輸出

+----+---------------+
| Id | Subject       |
+----+---------------+
| 1  | MySQL,MongoDB |
| 2  | MySQL,MongoDB |
| 3  | MongoDB       |
| 4  | MySQL         |
+----+---------------+
4 rows in set (0.00 sec)

下面是透過對列中特定id的MySQL 查詢來尋找字串計數的查詢。我們在這裡檢查 id 1 -

mysql> select Id,char_length(Subject) - char_length(REPLACE((Subject), ',', ''))+1 
   AS FreqSubject from DemoTable WHERE char_length(Subject) > 0 AND Id = 1;

輸出

+----+-------------+
| Id | FreqSubject |
+----+-------------+
| 1  | 2           |
+----+-------------+
1 row in set (0.02 sec)

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