Python 或 Excel：如何比较 2 列，然后在新列中写入第 3 列的值？

Question

I have 2 tables that look like this:

Table 1

| ID | Tel. |   Name  |
|:--:|:----:|:-------:|
| 1  | 1234 | Denis   |
| 2  | 4567 | Michael |
| 3  | 3425 | Peter   |
| 4  | 3242 | Mary    |

Table 2

| ID | Contact Date |
|:--:|:------------:|
| 1  | 2014-05-01   |
| 2  | 2003-01-05   |
| 3  | 2020-01-10   |
| 4  | NULL         |

Now I want to Compare the First Table with the second table with the ID column to look if contact 1 is already in the list where people were contacted. After this, I want to write the Contact Date into the first table to see the last contact date in the main table.

How would I do this?

Thanks for any answers!!

Answer 1

Here's a solution that might get your interest using MySQL ; Then if you want to implement it into Python will be easy.

First, Let's create our T1 Table AS CODED

create table T1(
    id integer primary key,
    tel integer, 
    name varchar(100)
    );

create table T2(
    id integer primary key,
    contactDate date
    );

Second Table T2

create table T2(
    id integer primary key,
    contactDate date
    );

Insertion Of T1 AND T2 :

-- Table 'T1' Insertion

insert into T1(id, tel, name) VALUES 
    (1, 1234, "Denis"),
    (2, 4567, "Michael"),
    (3, 3425,"Peter"),
    (4, 3242, "Mary");

-- Table 'T2' Insertion              
              
insert into T2(id, contactDate) VALUES 
    (1, 20140105),
    (2, 20030105),
    (3, 20201001),
    (4, Null);    

Then, Create T3 With the Select Statement for both tables using INNER JOIN For Joins Results

CREATE TABLE T3 AS
    SELECT T1.id, T1.name, T1.tel, T2.contactDate
    FROM T1
    INNER JOIN T2 ON T1.id=T2.id;

Then, SELECT to check the results

select * from T3;

OUTPUT

| id |   name  | tel  | contactDate |
|:--:|:-------:|------|-------------|
| 1  | Denis   | 1234 | 2014-01-05  |
| 2  | Michael | 4567 | 2003-01-05  |
| 3  | Peter   | 3425 | 2020-10-01  |
| 4  | Mary    | 3242 | NULL        |

I Hope This Helps. I was really trying to merge the T3 ---> contactDate with T1 for like 3 hours. But it was process heavy. I will attach Links that could help you more.

Reference

INNER JOIN

SQL ALTER TABLE Statement

SQL Server INSERT Multiple Rows

INSERT INTO SELECT statement overview and examples

SQL INSERT INTO SELECT Statement