I execute a query in my DB:
SELECT table1.*, tabl2.* FROM table1 JOIN table2 USING(id);
In these 2 tables i have a common column "id". What I have to ask, in order to get the column 'id' once time in the results and not twice?
I thought one solution is to write down in the query which columns I want. But If I want to avoid this (as there are many) ?
Will it work for you to name specific columns you need from both tables? something like:
SELECT table1.id, table2.other_column1, table2.other_column2 FROM table1 JOIN table2 USING(id);
You are selecting all fields from both tables by using (*)
Related
I need to build a query that I believe needs different types of joins, but I am not sure how to write it.
I have a customers table and an orders table. I need a query that will return 2 columns displaying the following:
1- list of all customer_id that have never had an order
2- list of all customer_ID that have 1 or more record in the orders table
I have this left join query but i feel like its missing something that indicates the customers column should not have a value on the orders table?
SELECT Customers.userid, Orders.userid
FROM Customers
LEFT JOIN ORDERS
ON Customers.userid=orders.USER_ID
I'm not sure I'm using right terminology here.
Basically I want to update entire "id" column using count(*) [485] as a delimiter, in an ascending order, so the resulting row value will correspond with rownumber (not the rowid).
If I understand you correctly, this should work for you:
UPDATE tbl_name SET id=rowid
EDIT
If that's is the case -> then it's a lit bit more tricky, since SQlite doesn't support variables declaration.
So what I suggest is,
To create temporary table from select of your original table which makes it's rowids to be as row numbers 1,2,3 etc...
Set it's rowNum (the needed row number column) as each rowid
Then replace the original table with it.
Like this: (assume original table called orig_name)
CREATE TABLE tmp_tbl AS SELECT rowNum FROM orig_name;
UPDATE tmp_tbl SET rowNum=rowid;
DROP TABLE orig_name;
CREATE TABLE orig_name AS SELECT rowNum FROM tmp_tbl;
DROP TABLE tmp_tbl;
Try this: http://www.sqlite.org/lang_createtable.html#rowid
You can use some inner database variables such as rowid, oid etc to get what you need.
[edit]
Think I just understood what you meant, you want for each insert action, add a value that is the total count of rows currently in the table?
If so, try something like this:
UPDATE tbl_name
SET id = (select count(*) from tbl_name)
WHERE yada_yada_yada
I'm working on a sqlite database and try to make a special request between two tables.
In the first table (table1 for example), i have two columns named "reference" and "ID". I want to search an ID in it, get it value in "reference" and display all informations from the table which have this value as name.
I try to find something on the internet but I didn't find an answer.
This is the request I made:
select * from (select Reference from table1 where Name='Value1')
It only give me the result of
select Reference from table1 where Name='Value1'
EDIT:
I want
select Reference from table1 where Name='Value1' => name of table
select * from name of table => show all elements
I'm new in sqlite but I hope you can help me.
Thank you by advance
Matt
If I understand your question correctly, I don't think there's a way to do it in sql completely (or at least not in a portable way). I'd recommend one of 3 solutions:
Do exactly what you want, but do some processing in Python. That means query your master table, then construct new query based on each of the rows returned.
If you have many tables, possibly changing dynamically - it may be a good idea to rethink your database design. Maybe you can move some of the changing table names into a new column and put your data in one table?
If you have only a few tables available as the Reference and they never change, you could join all the possible tables, like:
SELECT ... FROM table1
LEFT JOIN table2
ON table1.id = table2.id AND table1.Reference = "table2"
LEFT JOIN table3 ...
But you may need to explain it all a bit better...
I have 2 tables, headers with 2 millions rows and files with 30 rows.
I have a query that supposes to get the total number of headers for each directory.
The SQL looks like below:
SELECT files.dir_id, COUNT(*) AS "TOTAL"
FROM headers
LEFT JOIN files ON headers.file_id = files.file_id
GROUP BY files.dir_id
Currently, executing the SQL above is taking 20sec. How can I index it to make it faster?
I have tried CREATE INDEX IF NOT EXISTS HEADERS_FILE ON HEADERS(FILE_ID). This made GROUP BY file_id gets instant response (without left joining files table). However, it doesn't improve the performance for the original query above.
I'm thinking of something like CREATE INDEX INDEX_NAME ON HEADERS, FILES(FILE_ID, DIR_ID) should work. but I find no way in creating such index.
Appreciate for any help. Thanks!
The LEFT join prevents the database from using files as the outer table in the nested loop join.
Try using an inner join, and then adding the missing rows by hand; this might allow better optimization for the two subqueries:
SELECT files.dir_id, COUNT(*) AS "TOTAL"
FROM headers
-- LEFT JOIN expanded by hand for better optimization
INNER JOIN files ON headers.file_id = files.file_id
GROUP BY files.dir_id
UNION ALL
SELECT dir_id, 0
FROM files
WHERE file_id NOT IN (SELECT file_id
FROM headers)
If I have this statement,
SELECT table1.*, table2_1.`values` AS val_1
FROM table1 JOIN table2_1
ON table1.row_names=table2_1.row_names
I would actually like this the result joined back into table1. Any inclusion of a join statement after SELECT and before FROM gives me an error.
Why can I not save the results to a table, and is it possible to save it back to one of the original tables?
Because you do it the wrong way. SELECT statement will not modify you data no matter how much you want it. If you want to modify data, you need to use UPDATE statement.