Syntax error Resolve an error whenever multiple rows are returned in MySQL Benchmark?

Resolve an error whenever multiple rows are returned in MySQL Benchmark?

You will get an error whenever you return multiple rows in the benchmark. Return a scalar value or single row instead of multiple rows. The syntax is as follows −

SELECT yourColumnName FROM yourTableName WHERE yourCondition.

To understand the above syntax, let us create a table. The query to create a table is as follows −

mysql> create table UserDemo
   -> (
   -> UserId int,
   -> UserName varchar(20),
   -> RegisteredCourse varchar(10)
   -> );
Query OK, 0 rows affected (0.67 sec)

Insert some records in the table using insert command. The query is as follows −

mysql> insert into UserDemo values(1,'John','Java');
Query OK, 1 row affected (0.16 sec)
mysql> insert into UserDemo values(2,'Larry','C');
Query OK, 1 row affected (0.21 sec)
mysql> insert into UserDemo values(3,'Carol','C++');
Query OK, 1 row affected (0.11 sec)
mysql> insert into UserDemo values(4,'Mike','C#');
Query OK, 1 row affected (0.17 sec)

Display all records from the table using a select statement. The query is as follows −

mysql> select *from UserDemo;

The following is the output −

+--------+----------+------------------+
| UserId | UserName | RegisteredCourse |
+--------+----------+------------------+
|      1 | John     | Java             |
|      2 | Larry    | C                |
|      3 | Carol    | C++              |
|      4 | Mike     | C#               |
+--------+----------+------------------+
4 rows in set (0.00 sec)

Your benchmark error is as follows −

mysql> select benchmark(1000,(select RegisteredCourse from UserDemo));
ERROR 1242 (21000): Subquery returns more than 1 row

Since the subquery returned more than one row, therefore you need to return a single row. The query is as follows −

mysql> select RegisteredCourse from UserDemo where UserId=1;

The following is the output −

+------------------+
| RegisteredCourse |
+------------------+
| Java             |
+------------------+
1 row in set (0.00 sec)
Updated on: 2019-07-30T22:30:24+05:30

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