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How to check whether particular value in field in MySQL exists


How to check whether particular value in field in MySQL exists

By : YassineSIDKI
Date : November 22 2020, 03:03 PM
should help you out MySqlCommand.ExecuteScalar returns the first column of the first row returned by your query. This means (for your actual query) a NULL (if the username doesn't exist) or a string with the same username passed as parameter for the where condition. In any case not an integer.
So you just need to check if the object returned is null(Nothing in VB.NET).
code :
Dim result = cmd.ExecuteScalar()
if result IsNot Nothing then
  ... user exists....
query = "SELECT COUNT(*) FROM dbase.tblusers WHERE username = @username"
Private Sub btnCheckUser_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCheckUser.Click
    Dim userName = txtUsername.Text
    If IsUserExist(userName) Then
        MsgBox("user exists")
    Else
        MsgBox("user does not exists")
    End If
End Sub
With cmd
   .Parameters.AddWithValue("@username", userName)
   ....


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MySQL C API: check if a field exists

MySQL C API: check if a field exists


By : user155369
Date : March 29 2020, 07:55 AM
seems to work fine For anyone interested, this is something I wrote using the comments, and finally ended up using.
code :
if (mysql_query(con, "SELECT field FROM table WHERE userName='user1'")) 
{
    finish_with_error(con);
}

MYSQL_RES *result = mysql_store_result(con);

if (result == NULL) 
{
    finish_with_error(con);
}  

MYSQL_ROW row;
MYSQL_FIELD *field;

if (row = mysql_fetch_row(result))
{
    printf("%s\n", row[0]);
    db_pwd = row[0];
}
MySQL Trigger Check if Row Field Exists

MySQL Trigger Check if Row Field Exists


By : YoungNong
Date : March 29 2020, 07:55 AM
it fixes the issue The error isn't related to the columns referenced in the UPDATE statement.
The big problem is the unqualified reference to size in the trigger body. If the intent is to detect a change in the value assigned to size, we should be comparing the value of NEW.size to OLD.size.
code :
DELIMITER $$

DROP TRIGGER IF EXISTS tb_ins $$

CREATE TRIGGER tb_ins 
BEFORE UPDATE ON tb
FOR EACH ROW
BEGIN
   IF NOT (NEW.size <=> OLD.size) THEN
      -- value of size column has been modified
      BEGIN END;
   END IF;
END$$
MySQL - How to check if a value exists before appending to a TEXT Field?

MySQL - How to check if a value exists before appending to a TEXT Field?


By : Soham Acharya
Date : March 29 2020, 07:55 AM
hop of those help? It looks like event_types is a denormalized field, containing a comma-separated sequence of text strings. With respect, this is a notorious database design antipattern. The next programmer to work on your code will be very unhappy indeed.
I'll answer your question even though it pains me.
code :
FIND_IN_SET('testEvent', event_types)
  ...UPDATE event_types = IF(FIND_IN_SET('testEvent',event_types) > 0,
                             CONCAT(event_types, ',', 'testEvent'),
                             event_types)
CREATE TABLE event_types (
    event_id INT(11) NOT NULL,
    event_type VARCHAR(50) NOT NULL,
    PRIMARY KEY (event_id, event_type)
)
 INSERT IGNORE INTO event_types (event_id, event_type)
                         VALUES (1,       'testEvent');
  SELECT e.event_id, GROUP_CONCAT(t.event_type ORDER BY t.event_type) event_types
    FROM events e
    LEFT JOIN event_types t ON e.event_id = t.event_it
   GROUP BY e.event_id
  SELECT event_id FROM event_types WHERE event_type='testEvent')
MySQL: How to check if a field value exists in a comma separated field in the same table

MySQL: How to check if a field value exists in a comma separated field in the same table


By : user2515246
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , I have a table that contains two string values. The second column col2 contains a series of a comma separated strings. The following is a simple example: , You can do it with this:
code :
select *
from tablename 
where 
  concat(',', col2, ',') like
  concat('%,aaa:000.', substring_index(col1,'aaa:',-1), '/,%')
select *
from tablename 
where 
  concat(',', col2, ',') like
  concat('%,aaa:000.', substring_index(col1,'aaa:',-1), '/,%')
  or
  concat(',', col2, ',') like
  concat('%,aaa:000.', substring_index(col1,'aaa:',-1), ',%')
mysql check if field value exists in another table

mysql check if field value exists in another table


By : Jose Luis Acuna Camp
Date : March 29 2020, 07:55 AM
To fix the issue you can do Try JOIN these two tables and take products with ProductCode or SampleRefNum is null from STOCK_LIST
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