What would happen if we run SELECT WHERE columnName = zero in MySQL?

The following syntax will fetch all the values from the column −

select * from yourTableName where yourColumnName=0;

Let us first create a table −

mysql> create table DemoTable1791
     (
     FirstName varchar(20)
     );
Query OK, 0 rows affected (0.00 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1791 values('David');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1791 values('John');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1791 values('Carol');
Query OK, 1 row affected (0.00 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1791;

This will produce the following output −

+-----------+
| FirstName |
+-----------+
| David     |
| John      |
| Carol     |
+-----------+
3 rows in set (0.00 sec)

Here is the query wherein we are implementing select where value is zero −

mysql> select * from DemoTable1791 where FirstName=0;

This will produce the following output

+-----------+
| FirstName |
+-----------+
| David     |
| John      |
| Carol     |
+-----------+
3 rows in set, 3 warnings (0.00 sec)