I've seen enough answers to know you can't easily check for columns in SQLITE before adding. I'm trying to make a lazy person's node in Node-Red where you pass a message to SQLITE which is the query. Adding a table if it does not exist is easy.
msg.topic='create table IF NOT EXISTS fred (id PRIMARY KEY);'; node.send(msg);
it occurred to me that adding a table which had the names of the fields would be easy - and if the field name is not in the table.... then add the field. BUT you can't add multiple fields at once - so I can't do this...
msg.topic='create table IF NOT EXISTS fred (id PRIMARY KEY, myfields TEXT);'; node.send(msg);
The problem with THAT is that I can't add this in later, there's no way to check before adding a field it the table exists!
This is what I WANT
msg.topic='create table IF NOT EXISTS fred (id PRIMARY KEY, myfields TEXT);'; node.send(msg);
msg.topic='if not (select address from myfields) alter table fred add column address text';
I just cannot think of any way to do this - any ideas anyone (the idea is that the node-red node would input a table, field and value and if the table didn't exist it would be created, if the field didn't exist it would be created, all before trying to add in the value).
You won't be able to make the ALTER TABLE conditional in the SQL itself. You'll need to handle that from your calling script.
Alternately, simply attempt to add the column to the table and accept failure as an outcome. Assuming the table exists, the only failure reason you could encounter is that the column already exists.
If you'd like to do something more graceful, you can check if the column exists in advance, then conditionally run the SQL from your calling application.
Related
I am currently working on a database structure in SQLite Studio (not sure whether that's in itself important, but might as well mention), and error messages are making me wonder whether I'm just going at it the wrong way or there's some subtlety I'm missing.
Assume two tables, people-basics (person-ID, person-NAME, person-GENDER) and people-stats (person-ID, person-NAME, person-SIZE). What I'm looking into achieving is "Every record in people-basics corresponds to a single record in people-stats.", ideally with the added property that person-ID and person-NAME in people-stats reflect the associated person-ID and person-NAME in people-basics.
I've been assuming up to now that one would achieve this with Foreign Keys, but I've also been unable to get this to work.
When I add a person in people-basics, it works fine, but then when I go over to people-stats no corresponding record exists and if I try to create one and fill the Foreign Key column with corresponding data, I get this message: "Cannot edit this cell. Details: Error while executing SQL query on database 'People': no such column: people-basics.person" (I think the message is truncated).
The DDL I currently have for my tables (auto-generated by SQLite Studio based on my GUI operations):
CREATE TABLE [people-basics] (
[person-ID] INTEGER PRIMARY KEY AUTOINCREMENT
UNIQUE
NOT NULL,
[person-NAME] TEXT UNIQUE
NOT NULL,
[person-GENDER] TEXT
);
CREATE TABLE [people-stats] (
[person-NAME] TEXT REFERENCES [people-basics] ([person-NAME]),
[person-SIZE] NUMERIC
);
(I've removed the person-ID column from people-stats for now as it seemed like I should only have one foreign key at a time, not sure whether that's true.)
Alright, that was a little silly.
The entire problem was solved by removing hyphens from table names and column names. (So: charBasics instead of char-basics, etc.)
Ah well.
In APEX, when performing a Data Load (e.g. upload of a csv file into APEX application), is it possible to validate input data using a transformation rule?
For example, suppose to upload data about cars that have been sold this month.
The target table has the column car_manufacturer and num_car_sold.
The column car_manufacturer must accept only three values, say ('A1', 'A2', 'A3').
In a pseudo PLSQL, just to give an idea:
IF :car_manufacturer IN ('A1, A2, A3') then :car_manufacturer else <error>
How can I check this in the upload phase? Is it possible to use a transformation rule, in order that if it fails, it returns an error message? Other ways?
Thanks in advance.
You could put a constraint on the table definition as per the other answer, or if you only want the error message for when the Data Load is used, you can use a Table Lookup.
Go to Shared Components -> Data Load Definitions
Open the Data Load Definition that you want to edit
Create Table Lookup
Select the column (e.g. car_manufacturer)
Set the Table Lookup attributes to a table that contains the list of valid values (you'll need either a table or a view for this)
Leave Insert New Value set to No (If set to 'No' (the default) then a new record will not be created in the lookup table if the lookup column value(s) entered do not already exist. If set to 'Yes' then a record will be created in the lookup table using the upload column(s) and the Upload Key Column will be retrieved from the newly created record.)
Set Error Message to the message you want to return if a match is not found.
How about having a check constraint on the table for the column "car_manufacturer"?
ALTER TABLE TABLE_NAME
ADD CONSTRAINT CHECK_CAR_MANUFACTURER
CHECK ( CAR_MANUFACTURER in ('A1', 'A2', 'A3'));
I am trying to make the "BRFID" field the primary key in this table but I get the following error. (see screenshot). I don't see any other indexed field in the table. I am new to access, what am I doing wrong?
screenshot here
A primary key cannot have any duplicate values. Your problem is that there are duplicates entries in the BRFID field. You need to correct that and make every value in that field unique before it can be a Primary Key field.
In the Query Wizard, there is a way to generate a query that identifies duplicate values. Use that to find the duplicates. You'll have to come up with the way to correct the problem.
I want to insert a record into a sqlite table if its actually not inserted.
Let's say it has three fields pk, name, address
I want to INSERT new record with name if that name not added preveously.
Can we do with this in a single Query. Seems like its slightly different from SQL Queries sometimes.
Yes, you can do that with a single query.
INSERT ON CONFLICT IGNORE should help you: http://www.sqlite.org/lang_conflict.html
Put a unique key on the name, this will create a conflict when you try inserting a record if the name already exists.
The default is ABORT, so without the IGNORE, the statement will return an error. If you don't want that, use IGNORE.
If you can't make use of a UNIQUE INDEX in combination with INSERT INTO or INSERT OR IGNORE INTO, you could write a query like this;
INSERT INTO table (column)
SELECT value
WHERE NOT EXISTS (SELECT 1
FROM table
WHERE column = value)
I have a sqlite table that was originally created with:
PRIMARY KEY (`column`);
I now need to remove that primary key and create a new one. Creating a new one is easy, but removing the original seems to be the hard part. If I do
.indices tablename
I don't get the primary key. Some programs show the primary key as
Indexes: 1
[] PRIMARY
The index name is typically in the [].
Any ideas?
You can't.
PRAGMA INDEX_LIST('MyTable');
will give you a list of indices. This will include the automatically generated index for the primary key which will be called something like 'sqlite_autoindex_MyTable_1'.
But unfortunately you cannot drop this index...
sqlite> drop index sqlite_autoindex_MyTable_1;
SQL error: index associated with UNIQUE or PRIMARY KEY constraint cannot be dropped
All you can do is re-create the table without the primary key.
I the database glossary; a primary-key is a type of index where the index order is typically results in the physical ordering of the raw database records. That said any database engine that allows the primary key to be changed is likely reordering the database... so most do not and the operation is up to the programmer to create a script to rename the table and create a new one. So if you want to change the PK there is no magic SQL.
select * from sqlite_master;
table|x|x|2|CREATE TABLE x (a text, b text, primary key (`a`))
index|sqlite_autoindex_x_1|x|3|
You'll see that the second row returned from my quick hack has the index name in the second column, and the table name in the third. Try seeing if that name is anything useful.