All:
I am pretty new to SQL, I wonder how can I update certain field value across multiple tables in SQLITE3 database?
For example:
the database is company.db, inside it, there are 50 tables, each table has a column called company_name, now some company's names changed, so I need to update that info in all tables, I wonder how to do it in SQL?
Thanks
Related
Something went wrong during a structure synchronization between two databases.
One of our production databases now is missing a key table 'customers' (which just about every other table has foreign keys to)
I'm trying to recreate the table from last night's backup (I don't want to restore the entire db - just recreate this table as the data in it does not change that much and I don't want to lose the transactional data from today)
The hassle seems to be that all the foreign key data for this table still exists in INFORMATION_SCHEMA.KEY_COLUMN_USAGE and I am getting 121 and 150 errors when I try run the CREATE TABLE query.
I've manually deleted all FK to the missing table and I am still getting errno 150 when trying to recreate the table. Any ideas where else there might be lost references to this table that is stopping me creating it again?
This was eventually resolved by multiple consultations of the SHOW ENGINE INNODB STATUS query.
The missing table had various indexes - example on the customer name there was an index "customer_name_idx". The CREATE TABLE query asked for this index to be created. The show engine innodb status return was "could not create table because index customer_name_idx already exists."
There was no reference to this index, to any primary key or to the table itself in any of the meta-data tables - I checked
INFORMATION_SCHEMA.INNODB_SYS_INDEXES
INFORMATION_SCHEMA.TABLE_SCHEMA
INFORMATION_SCHEMA.STATISTICS -INFORMATION_SCHEMA.TABLE
so I could not explain why this error was being thrown.
My guess, after the fact, is that MySQL is holding a cached copy of the information_schema meta data in memory and was consulting that, and maybe that only gets refreshed if you restart MySQL?
The solution was to give the indexes new names as a short term fix, and to rename them during our next scheduled downtime.
Once these were made, the table was created and the backup data could be reinstated.
I want to save the results of my sqlite query in a new sqlite file. in other words, I want to have a new sqlite database with the data which resulted from my query on my previous data set.
All I have found on the internet was how to export the query results to csv or sql. but I want my new data set to be sqlite.
Also, is there any way to save the query results on the same data set (like what we do in excel)? Thank you!
You can ATTACH another database file to an existing connection and create or insert data into a table in that other database.
Something like:
ATTACH DATABASE 'other.db' AS other;
CREATE TABLE other.foo AS SELECT * FROM main.foo; -- create and populate a table
INSERT INTO other.bar SELECT * FROM main.foo; -- insert into an existing table
DETACH other;
I'm developing a Rust application for user registration via SSH (like the one working for SDF).
I'm using the SQLite3 database as a backend to store the information about users.
I'm opening the database file (or creating it if it does not exist) but I don't know the approach for checking if the necessary tables with expected structure are present in the database.
I tried to use PRAGMA schema_version for versioning purposes, but this approach is unreliable.
I found that there are posts with answers that are heavily related to my question:
How to list the tables in a SQLite database file that was opened with ATTACH?
How do I retrieve all the tables from database? (Android, SQLite)
How do I check in SQLite whether a table exists?
I'm opening the database file (or creating it if it does not exist)
but I don't know the approach for checking if the necessary tables
I found querying sqlite_master to check for tables, indexes, triggers and views and for columns using PRAGMA table_info(the_table_name) to check for columns.
e.g. the following would allow you to get the core basic information and to then be able to process it with relative ease (just for tables for demonstration):-
SELECT name, sql FROM sqlite_master WHERE type = 'table' AND name LIKE 'my%';
with expected structure
PRAGMA table_info(mytable);
The first results in (for example) :-
Whilst the second results in (for mytable) :-
Note that type is blank/null for all columns as the SQL to create the table doesn't specify column types.
If you are using SQLite 3.16.0 or greater then you could use PRAGMA Functions (e.g. pragma_table_info(table_name)) rather than the two step approach need prior to 3.16.0.
I have a live table in dynamo with about 28 million records in it.
The table has a number of GSI that I'd like to change to be LSIs however LSIs can only be created when the table is created.
I need to create a new table and migrate the data with minimum downtime. I was thinking I'd do the following:
Create the new table with the correct indexes.
Update the code to write records to the old and new table. When this starts, take a note of the timestamp for the first record.
Write a simple process to sync existing data for anything with a create date prior to my first date.
I'd have to add a lock field to the new table to prevent race conditions when an existing record is updated.
When it's all synced we'd swap to using the new table.
I think that will work, but it's fairly complicated and feels prone to error. Has anyone found a better way to do this?
Here is an approach:
(Let's refer to the table with GSIs as oldTable and the new table with LSIs as newTable).
Create newTable with the required LSIs.
Create a DynamoDB tirgger for the oldTable such that for every new record coming to the oldTable insert the same record to the newTable. (This logic needs to be in the AWS Lambda).
Make your application point to the newTable.
Migrate all the records from oldTable to newTable.
I have a massive database (~800 GB) with several indexed tables. I need to copy one table (including indexes) to a new database. Copying the table itself is pretty straightforward.
$ sqlite3 newDB
> attach database 'oldDB.db' as oldDB
> create table newTable as select * from oldDB.oldTable
But I can't seem to find any information on a way to also copy over an index. Is there any way to do this? Since the tables are so large I'd really like to avoid having to re-index them.
SQLite has no mechanism to copy index contents.
If this particular table would be the majority of the data in the database, the fastest way to copy it would be to copy the database file and then to drop all other tables.
But otherwise, there you cannot avoid the reindex operation.
Please note that CREATE TABLE ... AS ... does copy only the contents of the table, but not the complete table definition (such as column types or constraints).
Copying large table in a single transaction is not a good idea. If you really have to you should turn off journaling first (destination database):
PRAGMA journal_mode=OFF;
As the others have stated, the index cannot be broken out. I suspect that time spent copying the database and then dropping a very large table would be longer than just -> 1. creating the new destination database, 2. determining the original CREATE TABLE statement (from the SQLITE_MASTER table of the source database) and recreating the table in the destination database. Then 3. just ATTACH your destination database to the source database and INSERT INTO destinationdb.tablename SELECT * FROM sourcedb.tablename;* to get the copy rolling.