I have just started a full stack web developer course which includes PostgreSQL. I have been give some practice questions to do and when I clicked on run SQL it displays the id, first_name and last_name but when I entered in more lines of code to answer more questions and clicked on run SQL again, the id number changed to a completely different number and I don't understand why this is happening.
In the practice questions I was instructed to add more rows and then to update the entry with an id of 2 to something else but how can I update id 2 if the id numbers keep changing? id 2 wasn't even on the screen. What I understand of id serial primary key is that it auto increments the id when you add new rows but in this case the id keeps changing to random numbers, why does it do this? The screenshots are code from the course, not what I entered. http://sqlfiddle.com/#!17/a114f/2 this is the link but I am not sure if you anyone who has not signed up to the course can access it. Sorry if this is a really simple newbie question but I have spent a lot of time looking online and I really need to move forward.
As far as I can tell this is a bug in SQLFiddle.
Apparently the table definition (or something else) is shared with other users. If you do the same e.g. using db<>fiddle you always get the same ID after dropping and re-creating the tables:
db<>fiddle demo
SQLFiddle has never worked reliably for me anyway. Plus it seems to be stuck on a really old Postgres version. So you might use something different to practice your SQL skills or do your homework.
Like a_horse_with_no_name, I too prefer db<>fiddle for SQL code sharing. But if you're restricted to sqlfiddle for whatever reason, you can add a setval() command to your code to force the seeding value.
select setval('drivers_id_seq',1);
INSERT INTO drivers (first_name, last_name) VALUES ('Amy', 'Hua');
SELECT * from drivers;
See example here (link). Note that drivers_id_seq is a system-generated name that you can guess pretty easily (should you need to reseed the serial you create on another object).
In SQL Fiddle every time you click the button on the right its going to "rerun" your code.
However SQL Fiddle doesn't guarantee the primary keys are going to be the same, and isolates your code in such a way that definitely is causing the pk to increment.
http://sqlfiddle.com/#!17/a114f/2 Here's the original fiddle, and if you just jam on that submit button you can see the value changing each time.
Nothing in your code prevents duplication from concurring if you submitted it multiple times, but that would always have more than one row in the discover table.
Related
I have a sample of a stored procedure like this (from my previous working experience):
Select * from table where (id=#id or id='-999')
Based on my understanding on this query, the '-999' is used to avoid exception when no value is transferred from users. So far in my research, I have not found its usage on the internet and other company implementations.
#id is transferred from user.
Any help will be appreciated in providing some links related to it.
I'd like to add my two guesses on this, although please note that to my disadvantage, I'm one of the very youngest in the field, so this is not coming from that much of history or experience.
Also, please note that for any reason anybody provides you, you might not be able to confirm it 100%. Your oven might just not have any leftover evidence in and of itself.
Now, per another question I read before, extreme integers were used in some systems to denote missing values, since text and NULL weren't options at those systems. Say I'm looking for ID#84, and I cannot find it in the table:
Not Found Is Unlikely:
Perhaps in some systems it's far more likely that a record exists with a missing/incorrect ID, than to not be existing at all? Hence, when no match is found, designers preferred all records without valid IDs to be returned?
This however has a few problems. First, depending on the design, user might not recognize the results are a set of records with missing IDs, especially if only one was returned. Second, current query poses a problem as it will always return the missing ID records in addition to the normal matches. Perhaps they relied on ORDERing to ease readability?
Exception Above SQL:
AFAIK, SQL is fine with a zero-row result, but maybe whatever thing that calls/used to call it wasn't as robust, and something goes wrong (hard exception, soft UI bug, etc.) when zero rows are returned? Perhaps then, this ID represented a dummy row (e.g. blanks and zeroes) to keep things running.
Then again, this also suffers from the same arguments above regarding "record is always outputted" and ORDER, with the added possibility that the SQL-caller might have dedicated logic to when the -999 record is the only record returned, which I doubt was the most practical approach even in whatever era this was done at.
... the more I type, the more I think this is the oven, and only the great grandmother can explain this to us.
If you want to avoid exception when no value transferred from user, in your stored procedure declare parameter as null. Like #id int = null
for instance :
CREATE PROCEDURE [dbo].[TableCheck]
#id int = null
AS
BEGIN
Select * from table where (id=#id)
END
Now you can execute it in either ways :
exec [dbo].[TableCheck] 2 or exec [dbo].[TableCheck]
Remember, it's a separate thing if you want to return whole table when your input parameter is null.
To answer your id = -999 condition, I tried it your way. It doesn't prevent any exception
I need to replace all occurrences "google.com" that are met in the SQL db table Column1 with "newurl". It can be a full cell value, a part of it (substring of varchar()), can be met even several times in a cell.
Based on SO answer search-and-replace-part-of-string-in-database
this is what I need:
UPDATE
MyTable
SET
Column1 = Replace(Column, 'google.com', 'newurl')
WHERE
xxx
However, in that answer it is mentioned that
You will want to be extremely careful when doing this! I highly recommend doing a backup first.
What are the pitfalls of doing this query? Looks like it does the same what any texteditor would do by clicking on Replace All button. I don't think it is possible in my case to check the errors even with reserve copy as I would like to know possible errors in advance.
Any reasons to be careful with this query?
Again, I expect it replaces all occurences of google.com with 'newurl' in the Column1 of MyTable table in the SQL db.
Thank you.
Just create a test table, as a replica of your original source table, complete the update on there and check results.
You would want to do this as good SQL programming practice to ensure you don't mess up columns that should not be updated.
Another thing you can do is get a count of the records before hand that fit the criteria using a SELECT statement.
Run your update statement and if it's a 1-1 match on count, you should be good to go.
The only thing i can think of that would happen negatively in this respect is that additional columns get updated. Your WHERE clause is not specific for us to see, so there's no way to validate that what you're doing will do what you expect it to.
I think the person posting the answer is just being cautious - This will modify the value in Column1 for every row in MyTable, so make sure you mean it when you execute. Another way to be cautious would be to wrap it in a transaction so you could roll it back if you don't like the results.
Before you answer, let me emphasize that this is a question related to the Ingres RDBMS .
As many other Ingres users who complained about in the past on forums, I also experience the access issue when AUTO_INCREMENT is used... I need to find out the sequence used for the AUTO_INCREMENT field, so I can grant access to it in order to prevet some annoying exceptions...
Yes, when exception is thrown (JDBC) I get the name of the sequence in question, and I can fix it. But in the case I have bunch of tables, I may want to fix them all with a script.
How to find what sequence is used? (I mean its name)
Similarly, how to find out in what table is certain identity sequence used?
Example: $iiidentity_sequence_0012936
Try this
SELECT table_name,column_name, column_default_val
FROM iicolumns
WHERE column_always_ident = 'Y'
OR column_bydefault_ident = 'Y'
ORDER BY 1,2
I am writing a log viewer app in ASP.NET / C#. There is a report window, where it will be possible to check some information about the whole database. One kind of information there I want to display on the screen is the number of times each generator (an entity in my domain, not Firebirds sequence) appears in the table. How do I do that using COUNT ?
Do I have to :
Gather the key for each different generator
Run one query for each generator key using count
Display it somehow
Is there any way that I can do it without having to do two queries to the database? The database size can be HUGE, and having to query it "X" times where "X" is the number of generators would just suck.
I am using a Firebird database, is there any way to fetch this information from any metadata schema or there is no such thing available?
Basically, what I want is to count each occurrence of each generator in the table. Result would be something like : GENERATOR A:10 times,GENERATOR B:7 Times,Generator C:0 Times and so on.
If I understand your question correctly, it is a simple matter of using the GROUP BY clause, e.g.:
select
key,
count(*)
from generators
group by key;
Something like the query below should be sufficient (depending on your exact structure and requirements)
SELECT KEY, COUNT(*)
FROM YOUR_TABLE
GROUP BY KEY
I solved my problem using this simple Query:
SELECT GENERATOR_,count(*)
FROM EVENTSGENERAL GROUP BY GENERATOR_;
Thanks for those who helped me.
It took me 8 hours to come back and post the answer,because of the StackOverflow limitation to answer my own questions based in my reputation.
Basically, I am the new IT type guy, old guy left a right mess for me! We have a MS-Access DB which stores the answers to an online questionnaire, this particular DB has about 45,000 records and each questionnaire has 220 questions. The old guy, in his wisdom decided to store the answers to the questionnaire questions as text even though the answers are 0-5 integers!
Anyway, we now need to add a load of new questions to the questionnaire taking it upto 240 questions. The 255 field limit for access and the 30ish columns of biographical data also stored in this database means that i need to split the DB.
So, I have managed to get all the bioinfo quite happily into a new table with:
SELECT id,[all bio column names] INTO resultsBioData FROM results;
this didn't cause to much of a problem as i am not casting anything, but for the question data i want to convert it all to integers, at the moment I have:
SELECT id,CInt(q1) AS nq1.......CInt(q220) AS nq220 INTO resultsItemData FROM results;
This seems to work fine for about 400 records but then just stops, I thought it may be because it hit something it cant convert to a integer to start with, so i wrote a little java program that deleted any record where any of ther 220 answers wasnt 0,1,2,3,4 or 5 and it still gives up around 400 (never the same record though!)
Anyone got any ideas? I am doing this on my test system at the moment and would really like something robust before i do it to our live system!
Sorry for the long winded question, but its doing my head in!
I'm unsure whether you're talking about doing the data transformation in Access or SQL Server. Either way, since you're redesigning the schema, now is the time to consider whether you really want resultsItemData table to include 200+ fields, from nq1 through nq220 (or ultimately nq240). And any future question additions would require changing the table structure again.
The rule of thumb is "columns are expensive; rows are cheap". That applies whether the table is in Access or SQL Server.
Consider one row per id/question combination.
id q_number answer
1 nq1 3
1 nq2 1
I don't understand why your current approach crashes at 400 rows. I wouldn't even worry about that, though, until you are sure you have the optimal table design.
Edit: Since you're stuck with the approach you described, I wonder if it might work with an "append" query instead of a "make table" query. Create resultsItemData table structure and append to it with a query which transforms the qx values to numeric.
INSERT INTO resultsItemData (id, nq1, nq2, ... nq220)
SELECT id, CInt(q1), CInt(q2), ... CInt(q220) FROM results;
Try this solution:
select * into #tmp from bad_table
truncate table bad_table
alter bad_table alter column silly_column int
insert bad_table
select cast(silly_column as int), other_columns
from #tmp
drop table #tmp
Reference: Change type of a column with numbers from varchar to int
Just wrote a small java program in the end that created the new table and went through each record individually casting the fields to integers, takes about an hour and a half to do the whole thing though so i am still after a better solution when i come to do this with the live system.