I am having a table Table1 with columns id1, id2, id3 all the columns are nullable
I may enter null or value to all columns in rows.
My question is I need to select the rows whose all the column values should not be null.
Thanks
There are totally around 300 columns in the table. I can't do the is null property for all the columns in where condition.
The answer to use a "function" to test the null-values is correct. The syntax depends on the database. If ISNULL() does not exist in your database then try:
SELECT * FROM Table1 WHERE id1 IS NOT NULL AND id2 IS NOT NULL AND id3 IS NOT NULL
And there is no way to short this down even if you have 300 fields in your table.
Don't understand why this question is getting negitive reviews - This question can be extended to people who inherited a large table from a non-programmer in a community (I know from previous experience), and likewise if the table is unknown. To downgrade this because its '300' columns is pointless IMO.
You need to do this:
SELECT *
FROM yourtable
WHERE
column1 IS NOT NULL
AND column2 IS NOT NULL
AND column3 IS NOT NULL
AND ....
Best bet is to either rethink the design of your tables, splitting them if required.
otherwise best bet is do it progmatically - grab the table metadata, itterate through the columns and drynamically create the SQL from there. Most coding languages have access to the tables metadata, failing that a second SQL is required for it.
But, best bet is to think how can I design the table better.
Are you saying you want to select the rows where none of the columns are null?
SELECT id1, id2, id3
FROM Table1
WHERE id1 IS NOT NULL AND id2 IS NOT NULL AND id3 IS NOT NULL
Sorry - I might be being a bit thick here. You're trying to get back the rows that have got SOMETHING in one of the columns (other than the id column)?
Can't you do;
create vw_View_Fields1to5 as
select id from employees
where name is not null or description is not null or field3 is not null
or field4 is not null or field5 is not null;
create vw_View_Fields6to10 as
select id from employees
where field6 is not null or field7 is not null or field8 is not null
or field 9 is not null or field10 is not null;
(etc)
select id from vw_View_Fields1to5
union
select id from vw_View_Fields6to10 .... (etc)
You'd have to take a DISTINCT or something to cut down the rows that fall into more than one view, of course.
If you want the rows back that have NOTHING in any column other than id, you'd switch 'or blah is not null' to be 'and blah is null' (etc).
Does that make sense... or am I missing something? :-)
EDIT: Actually, I believe the UNION process will only bring back distinct rows anyway (as opposed to UNION ALL), but I could be wrong - I haven't actually tried this.... (yet!)
you can try CLR stored procedure (if you're using SQL Server) or move this logic to the other layer of your application using C# or whatever language you're using.
another option is to create the query dynamically, concatenating your WHERE clause and EXECute your dynamically generated query.
Are you just reading the data, or will you want to try and update the rows in question?
I'm just wondering if there's something you can go by making a half-dozen views, each one based on say 50 columns being NOT NULL, and then linking them with some kind of EXISTS or UNION statement?
Can you tell us a bit more about what you want to do with your result set?
For the first time whatever Georgi or engram or robsoft is the way. However for subsequent stuff you can if possible alter the table and add one more column, called CSELECTFLAG, and initially updated this to Y for all columns that have values and N for others. Everytime there is an insert this needs to be updated. This would help make your subsequent queries faster and easier.
Related
Similar to this question and this solution for PostgreSQL (in particular "INSERT missing FK rows at the same time"):
Suppose I am making an address book with a "Groups" table and a "Contact" table. When I create a new Contact, I may want to place them into a Group at the same time. So I could do:
INSERT INTO Contact VALUES (
"Bob",
(SELECT group_id FROM Groups WHERE name = "Friends")
)
But what if the "Friends" Group doesn't exist yet? Can we insert this new Group efficiently?
The obvious thing is to do a SELECT to test if the Group exists already; if not do an INSERT. Then do an INSERT into Contacts with the sub-SELECT above.
Or I can constrain Group.name to be UNIQUE, do an INSERT OR IGNORE, then INSERT into Contacts with the sub-SELECT.
I can also keep my own cache of which Groups exist, but that seems like I'm duplicating functionality of the database in the first place.
My guess is that there is no way to do this in one query, since INSERT does not return anything and cannot be used in a subquery. Is that intuition correct? What is the best practice here?
My guess is that there is no way to do this in one query, since INSERT
does not return anything and cannot be used in a subquery. Is that
intuition correct?
You could use a Trigger and a little modification of the tables and then you could do it with a single query.
For example consider the folowing
Purely for convenience of producing the demo:-
DROP TRIGGER IF EXISTS add_group_if_not_exists;
DROP TABLE IF EXISTS contact;
DROP TABLE IF EXISTS groups;
One-time setup SQL :-
CREATE TABLE IF NOT EXISTS groups (id INTEGER PRIMARY KEY, group_name TEXT UNIQUE);
INSERT INTO groups VALUES(-1,'NOTASSIGNED');
CREATE TABLE IF NOT EXISTS contact (id INTEGER PRIMARY KEY, contact TEXT, group_to_use TEXT, group_reference TEXT DEFAULT -1 REFERENCES groups(id));
CREATE TRIGGER IF NOT EXISTS add_group_if_not_exists
AFTER INSERT ON contact
BEGIN
INSERT OR IGNORE INTO groups (group_name) VALUES(new.group_to_use);
UPDATE contact SET group_reference = (SELECT id FROM groups WHERE group_name = new.group_to_use), group_to_use = NULL WHERE id = new.id;
END;
SQL that would be used on an ongoing basis :-
INSERT INTO contact (contact,group_to_use) VALUES
('Fred','Friends'),
('Mary','Family'),
('Ivan','Enemies'),
('Sue','Work colleagues'),
('Arthur','Fellow Rulers'),
('Amy','Work colleagues'),
('Henry','Fellow Rulers'),
('Canute','Fellow Ruler')
;
The number of values and the actual values would vary.
SQL Just for demonstration of the result
SELECT * FROM groups;
SELECT contact,group_name FROM contact JOIN groups ON group_reference = groups.id;
Results
This results in :-
1) The groups (noting that the group "NOTASSIGNED", is intrinsic to the working of the above and hence added initially) :-
have to be careful regard mistakes like (Fellow Ruler instead of Fellow Rulers)
-1 used because it would not be a normal value automatically generated.
2) The contacts with the respective group :-
Efficient insertion
That could likely be debated from here to eternity so I leave it for the fence sitters/destroyers to decide :). However, some considerations:-
It works and appears to do what is wanted.
It's a little wasteful due to the additional wasted column.
It tries to minimise the waste by changing the column to an empty string (NULL may be even more efficient, but for some can be confusing)
There will obviously be an overhead BUT in comparison to the alternatives probably negligible (perhaps important if you were extracting every Facebook user) but if it's user input driven likely irrelevant.
What is the best practice here?
Fences again. :)
Note Hopefully obvious, but the DROP statements are purely for convenience and that all other SQL up until the INSERT is run once
to setup the tables and triggers in preparation for the single INSERT
that adds a group if necessary.
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...
So I have a table with data about an image. The table looks something like this...
ROWID|title|description|file_path
The file path contains the name of the image. I want to rename the image to match the ROWID.
How do I get the latest ROWID? I need to also account for rows that have been deleted as I am using this as an autoincremented primary key. Because, if a row within the table has been deleted it is possible for the table to look like this...
1|title A|description A|..\fileA.jpg
2|title B|description B|..\fileB.jpg
5|title E|description E|..\fileE.jpg
7|title G|description G|..\fileG.jpg
On top of that there could be one or more rows that have been deleted so the next ROWID could be 10 for all I know.
I also need to account for an fresh new table or a table that has had all data deleted and the next ROWID could be 1000.
In summary, I guess the real question is; Is there a way to find out what the next ROWID will be?
If you have specified AUTOINCREMENT in primary key field and table is not empty this query will return latest ROWID for table MY_TABLE:
SELECT seq
FROM sqlite_sequence
WHERE name = 'MY_TABLE'
What language? Looks like the c API has the following function:
sqlite3_int64 sqlite3_last_insert_rowid(sqlite3*);
http://www.sqlite.org/c3ref/last_insert_rowid.html
You could also just do:
select MAX(rowid) from [tablename];
Unfortunately neither of these methods completely worked the way I needed them to, but what i did end up doing was....
insert data into table with the fields I needed the rowid for filled with 'aaa'
then updated the rows with the data.
This seemed to solve my current issue. Hopefully it doesn't cause another issue down the road.
I think last_insert_rowid is what you want, usually.
Note that the rowid behavior is different depending on the autoincrement flag - either it will monotonically increase, or it will assume any free id. This will not usually affect any smaller use cases though.
Maybe i should do this in C# but i have more then one row with linkId X. I would like to remove it but i am unsure how. In code i could just use a foreach from 0 to n and remove any found rows with a greater (or !=) id but thats in code. Is there a less difficult way of doing it using sqlite?
Assuming the table's name is tableName and there is a primary key field named id, the following sql would do it. I think the following SQL query is general enough and should be able to be executed under any database engine.
delete from tableName
where id not in (
select min(id) from tableName
group by linkId
)
I want to get a number of rows in my table using max(id). When it returns NULL - if there are no rows in the table - I want to return 0. And when there are rows I want to return max(id) + 1.
My rows are being numbered from 0 and autoincreased.
Here is my statement:
SELECT CASE WHEN MAX(id) != NULL THEN (MAX(id) + 1) ELSE 0 END FROM words
But it is always returning me 0. What have I done wrong?
You can query the actual number of rows withSELECT Count(*) FROM tblName
see https://www.w3schools.com/sql/sql_count_avg_sum.asp
If you want to use the MAX(id) instead of the count, after reading the comments from Pax then the following SQL will give you what you want
SELECT COALESCE(MAX(id)+1, 0) FROM words
In SQL, NULL = NULL is false, you usually have to use IS NULL:
SELECT CASE WHEN MAX(id) IS NULL THEN 0 ELSE (MAX(id) + 1) END FROM words
But, if you want the number of rows, you should just use count(id) since your solution will give 10 if your rows are (0,1,3,5,9) where it should give 5.
If you can guarantee you will always ids from 0 to N, max(id)+1 may be faster depending on the index implementation (it may be faster to traverse the right side of a balanced tree rather than traversing the whole tree, counting.
But that's very implementation-specific and I would advise against relying on it, not least because it locks your performance to a specific DBMS.
Not sure if I understand your question, but max(id) won't give you the number of lines at all. For example if you have only one line with id = 13 (let's say you deleted the previous lines), you'll have max(id) = 13 but the number of rows is 1. The correct (and fastest) solution is to use count(). BTW if you wonder why there's a star, it's because you can count lines based on a criteria.
I got same problem if i understand your question correctly, I want to know the last inserted id after every insert performance in SQLite operation. i tried the following statement:
select * from table_name order by id desc limit 1
The id is the first column and primary key of the table_name, the mentioned statement show me the record with the largest id.
But the premise is u never deleted any row so the numbers of id equal to the numbers of rows.
Extension of VolkerK's answer, to make code a little more readable, you can use AS to reference the count, example below:
SELECT COUNT(*) AS c from profile
This makes for much easier reading in some frameworks, for example, i'm using Exponent's (React Native) Sqlite integration, and without the AS statement, the code is pretty ugly.