Join many tables sql [closed] - mysql

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I want to create a view of my database. \in fact, my database contains around 20 tables and i want to join the tables based on the foreign keys but there are some duplicates columns. Is there an easy and fast way to do it ?

Answer 1

Here's something that might help. You'll have to list out the columns if you do not want the dupes. You can run
SQL Fiddle Example
select group_concat(concat(table_name,'.', column_name) separator ', ')
from information_schema.columns
where table_name in ('Students', 'ClassRoster');
This will list [table_name].[column_name] for all the columns in the tables you specify in one long string. You can then copy the result and paste it next to the SELECT in your query and remove all the dupe columns if you know them. This query will show columns where there is more than one and show the table as well.
select table_name, column_name
from INFORMATION_SCHEMA.COLUMNS
where column_name in (
select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS
group by COLUMN_NAME
having count(1) > 1)
order by column_name
It still is manual but will save you some time. With a little more effort you could tweak the queries to where the whole process is just one query and not manually remove anything.

Answer 2

Just determined which columns you need in your view and use AS to assign a specific name to all of them.
This is an example. Both table have col1 and col2 :
SQL Fiddle
MySQL 5.5.32 Schema Setup:
CREATE TABLE Table1
(`Id` int, `Col1` varchar(1), `Col2` varchar(1), `Id2` int)
;
INSERT INTO Table1
(`Id`, `Col1`, `Col2`, `Id2`)
VALUES
(1, 'A', 'B', 1),
(2, 'B', 'C', 2),
(3, 'D', 'E', 3)
;
CREATE TABLE Table2
(`Id` int, `Col1` varchar(1), `Col2` varchar(1))
;
INSERT INTO Table2
(`Id`, `Col1`, `Col2`)
VALUES
(1, 'A', 'B'),
(2, 'B', 'C'),
(3, 'D', 'E')
;
Query 1:
SELECT Table1.Id as ID,
Table1.Col1 as COL1,
Table1.Col2 as COL2,
Table2.Col1 as COL3,
Table2.Col2 as COL4
FROM Table1
INNER JOIN Table2 ON Table1.Id2 = Table2.Id
Results:
| ID | COL1 | COL2 | COL3 | COL4 |
|----|------|------|------|------|
| 1 | A | B | A | B |
| 2 | B | C | B | C |
| 3 | D | E | D | E |

Answer 3

You Should Use Alias in joining like this...
Select E.Name , U.Name,E.Age,U.Age
From
TblEmployee E
inner join
TblUser U on E.EmployeeId = U.EmployeeId
Note : The above Query is only a Example So that you can go ahead
Edit: you can also do your column name what you want like this
Select E.* , U.*, E.Age as Employee Age ,U.Age as UserAge
/* you can specify some column by E.Name and if you do not want then simplye do E.* by doing thing every column of your that table will be selected */
From TblEmployee E
inner join
TblUser U on E.EmployeeId = U.EmployeeId