How to copy data from one table to another (where both have other fields too that are not in common)?

Detailed insights to facilitate precision

Handling distinct columns

When encountering distinct columns among tables, customize your SELECT query to align with the layout of the destination table:

-- Get those exact columns with surgical precision! 💉💊
INSERT INTO Destination (ID, Country)
SELECT ID, Country
-- No extra columns invited to this party 🎉
FROM Source
WHERE condition_if_necessary;  -- We need bouncer conditions for the VIP club.


Taking care of updates

Targeting to update existing records sourced from another table using a common key? The UPDATE with a subquery, is your trusted ally (though SQLite gets quirky here):

-- SQLite enters the update party with a subquery disguise
UPDATE Destination
SET Destination.Country = (SELECT Source.Country FROM Source WHERE Source.ID = Destination.ID)
WHERE EXISTS (SELECT 1 FROM Source WHERE Source.ID = Destination.ID);  -- Knock, knock. Who's there? Exist. Exist Who? Existential crisis!


Best practices and preventive measures

Let's keep data loss at bay with table backups before trying out any data modifications. Trying the process with a designated subset of data is a sound practice for preserving data quality and reliability.

Eradicating redundancy with normalization

Normalization is a gardener's trick to minimize duplicate efforts. A consolidated list of shared qualities (like our Tulips), in a detached table, can streamline information retrieval.

Distinguishing between SQLite and SQL Server

Diversity is the name of the game when comparing SQLite and SQL Server. Each offering unique functions and methods for data manipulation. A chess player needs to know the moves, so does a developer!

Embracing virtual tables for superior performance

SQLite introduces its own superhero, virtual tables, as an impressive tool for efficient querying and non-traditional data resource management.

Time to level up: In-depth tricks

Tackling null values with COALESCE

Nulls during data transfer can be a cloud on a sunny day. SQLite's coalesce function is your silver lining providing a fallback value when nulls make an appearance:

-- Actual conversation: null values say, 'I don't exist.', COALESCE replies, 'I got your back!'
SELECT COALESCE(column_name, 'default_value') FROM table_name;


Considering MERGE as a potent alternative

Switch to SQL Server and MERGE becomes an attractive choice. It's a one-stop solution for complex operations like inserting, updating, and deleting rows from a table using another table's data.

Efficient updates with join

SQLite misses the direct JOIN feature in an UPDATE statement; subqueries are your saviour. SQL Server users get a direct shot:

UPDATE dest
SET dest.Country = src.Country
FROM Destination AS dest
INNER JOIN Source AS src
ON dest.ID = src.ID;


SQLite caution: altering tables

SQLite acts tricky while modifying tables- dropping a column or changing a column's type leads to a dead-end. Keep these limitations within sight to avert unwanted surprises.