SQLite: How to Automatically Rename Columns from Same Table Join

sqlite

When I join two tables to avoid conflicts I use column aliases. But that is prone to errors if there a lot of columns. Also, some ORMS require to use hardcoded or dynamic prefixes to column names. Is there automatic way to rename columns in such a way that all columns from T22 start with "c_t22_" and all columns from T23 start with "c_t23_"?

select T1.id,
       T1.p1, T21.name as p1_name,
       T1.p2, T22.name as p2_name,
       T1.p3, T23.name as p3_name
from T1
join T2 as T21 on T1.p1 = T21.id,
join T2 as T22 on T1.p2 = T22.id,
join T2 as T23 on T1.p3 = T23.id

Best Answer

SQLite is designed as a small, embedded database to be accessed from a 'real' programming language, so it has no built-in mechanism for dynamic SQL.

You have to construct the SQL query from inside that other programming language; something like this:

cols = []
for tab in tables:
    for col in columns:
       cols.append("c_{}_{}".format(tab, col))
sql = "SELECT " + ", ".join(cols) + " ..."
execute(sql)

Related Solutions

Showing data in a table horizontally

It looks to me like you are trying to 'pivot' the data, which can be done with multiple case statements:

test data:

create table timestream(
  idTimestream integer primary key autoincrement
, time int not null
, value float not null
, idSensor integer not null);

insert into timestream(time, value, idSensor) values(1,0.1,100);

insert into timestream(time, value, idSensor) values(1,0.2,101);

insert into timestream(time, value, idSensor) values(1,0.3,102);

insert into timestream(time, value, idSensor) values(2,0.4,101);

query:

select time, sum(case idSensor when 100 then value end) as s100,
             sum(case idSensor when 101 then value end) as s101,
             sum(case idSensor when 102 then value end) as s102
from timestream
group by time;

time | s100 | s101 | s102
:--- | :--- | :--- | :---
1    | 0.1  | 0.2  | 0.3 
2    | null | 0.4  | null

dbfiddle here

Postgresql – Advice on scripting a “whitewashed” and downsized development db from main db

What you're referring to is usually called Test Data Management. There are several commercial solutions, e.g. IBM Optim Test Data Management (disclosure: I work for IBM, but don't speak for them). I'm not aware of any free products that can perform that function, so I'm afraid you'll have to stick to your Python scripts unless you have deep pockets.

On a side note, I would suggest using the same database platform, i.e. PostgreSQL, for both production and development -- it will probably save you some troubleshooting time later.

Best Answer

Related Solutions

Showing data in a table horizontally

Postgresql – Advice on scripting a “whitewashed” and downsized development db from main db

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