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Is there a way to use 2 columns to uniquely identify a row in MYSQL?


Is there a way to use 2 columns to uniquely identify a row in MYSQL?

By : Bellito
Date : September 20 2020, 04:00 AM
Any of those help You can try adding a unique constraint on the combination of first and last names:
code :
ALTER TABLE user
ADD CONSTRAINT name_unique UNIQUE KEY (firstname, lastname);
CREATE TABLE `user` (
    firstname` VARCHAR(10) NOT NULL,
    lastname` VARCHAR(10) NOT NULL,
    ...
    PRIMARY KEY (firstname, lastname)
)


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Uniquely identify HTML table in order to count columns

Uniquely identify HTML table in order to count columns


By : Sun
Date : March 29 2020, 07:55 AM
With these it helps I need to append columns to an HTML table in a specific location. This topic discusses doing that - pretty handy! My problem is that the columnCount() function shown below does not have the ability to target a specific table. It counts all TDs present in the HTML which ends up causing problems when generating an index value. , Take the table ID as a parameter:
code :
function countColumn(tableID) {
   var colCount = 0;
   $('#' + tableID + ' tr:nth-child(1) td').each(function () {
       if ($(this).attr('colspan')) {
           colCount += +$(this).attr('colspan');
       } else {
           colCount++;
       }
   });
   return colCount;
}
$.fn.colCount = function() {
   var colCount = 0;
   $('tr:nth-child(1) td', this).each(function () {
       if ($(this).attr('colspan')) {
           colCount += +$(this).attr('colspan');
       } else {
           colCount++;
       }
   });
   return colCount;
};
Uniquely identify same column name of two different table after join - mysql

Uniquely identify same column name of two different table after join - mysql


By : Neha Fakirde
Date : March 29 2020, 07:55 AM
I wish this help you As an IDEA, what you can do is, if you want to avoid columns of specific table & your statements have multiple table, you can try following,
Suppose you have 20 columns in table a & 5 columns in table b, you want to avoid col2,col3 & col4 of table b. Standard method is that you should write name of all columns of table a & required columns of table b. But you can avoid to write long list of 20 columns of table by writing a.* & then type required columns of table b. Please see below statement.
code :
Select a.*,b.col1,b.col4,b.col5 from a,b
Should I use my two columns that uniquely identify a record as primary key?

Should I use my two columns that uniquely identify a record as primary key?


By : Jun
Date : March 29 2020, 07:55 AM
wish helps you It is a good practise to never have your business values as table's primary key and always to use synthetic, e.g. autoincrement, values for this. You will make your life easier in the future when business requirements change :)
We are currently struggling with exactly this situation. Have a column with business values as a primary key for 2 years and now painfully introducing an autoincrement one.
How do I uniquely identify a database in MySql?

How do I uniquely identify a database in MySql?


By : Krenare Rexhepi
Date : March 29 2020, 07:55 AM
With these it helps No, the schema name is the identifier.
You may want to set server_id uniquely on each of your MySQL instances. This is an integer in the range 1 through 232-1 that you configure in your MySQL instance's my.cnf file.
code :
SELECT @@server_id;
Determine if columns of a pandas dataframe uniquely identify the rows

Determine if columns of a pandas dataframe uniquely identify the rows


By : user1524436
Date : March 29 2020, 07:55 AM
I hope this helps you . I'm looking for a way to determine if a column or set of columns of a pandas dataframe uniquely identifies the rows of that dataframe. I've seen this called the isid function in Stata. , You could make an index and check its is_unique attribute:
code :
import pandas as pd

df1 = pd.DataFrame([(1,2),(1,2)], columns=list('AB'))

df2 = pd.DataFrame([(1,2),(1,3)], columns=list('AB'))

print(df1.set_index(['A','B']).index.is_unique)
# False

print(df2.set_index(['A','B']).index.is_unique)
# True
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