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How can I add a new column which counts the number of rows as serial number in MySQL?
To add a new column that counts the number of rows as serial number, you can use the global variable in select statement.
Let us create a table. The query to create a table is as follows:
mysql> create table addColumnToCountAsSerialNumber -> ( -> Id int, -> Name varchar(20), -> Age int, -> Salary int -> ); Query OK, 0 rows affected (0.80 sec)
Insert some records in the table using insert command. The query is as follows:
mysql> insert into addColumnToCountAsSerialNumber values(10,'John',23,8576); Query OK, 1 row affected (0.10 sec) mysql> insert into addColumnToCountAsSerialNumber values(12,'Carol',21,4686); Query OK, 1 row affected (0.14 sec) mysql> insert into addColumnToCountAsSerialNumber values(9,'Mike',22,38585); Query OK, 1 row affected (0.11 sec) mysql> insert into addColumnToCountAsSerialNumber values(15,'Sam',25,38586); Query OK, 1 row affected (0.16 sec) mysql> insert into addColumnToCountAsSerialNumber values(20,'Bob',26,43544); Query OK, 1 row affected (0.17 sec) mysql> insert into addColumnToCountAsSerialNumber values(39,'Larry',29,485886); Query OK, 1 row affected (0.16 sec)
Display all records from the table using select statement. The query is as follows:
mysql> select *from addColumnToCountAsSerialNumber ;
The following is the output:
+------+-------+------+--------+ | Id | Name | Age | Salary | +------+-------+------+--------+ | 10 | John | 23 | 8576 | | 12 | Carol | 21 | 4686 | | 9 | Mike | 22 | 38585 | | 15 | Sam | 25 | 38586 | | 20 | Bob | 26 | 43544 | | 39 | Larry | 29 | 485886 | +------+-------+------+--------+ 6 rows in set (0.00 sec)
The following is the query to count each row as a serial number:
mysql> select @globalVar:=@globalVar+1 RowCount,tblColumns.* -> from (select @globalVar:=0) initializeGlobalVariable,addColumnToCountAsSerialNumber tblColumns;
The following is the output displaying the count in a new column “RowCount”:
+----------+------+-------+------+--------+ | RowCount | Id | Name | Age | Salary | +----------+------+-------+------+--------+ | 1 | 10 | John | 23 | 8576 | | 2 | 12 | Carol | 21 | 4686 | | 3 | 9 | Mike | 22 | 38585 | | 4 | 15 | Sam | 25 | 38586 | | 5 | 20 | Bob | 26 | 43544 | | 6 | 39 | Larry | 29 | 485886 | +----------+------+-------+------+--------+ 6 rows in set (0.06 sec)
Updated on: 30-Jul-2019
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