Sql Update from One Table to Another Based on ID Match

Cooking Up SQL Dialects

Stir the SQL pot, and we see a mix of dialects, each with its own flavors for the update recipe:

For SQL Server, whip this up. We call it UPDATE FROM JOIN:

UPDATE Table1
SET Table1.target_column = Table2.source_column
FROM Table2
WHERE Table1.ID = Table2.ID;
-- SQL Server says: I like it "FROM" the top!


MySQL or MariaDB offers a slightly tweaked soup:

UPDATE Table1, Table2
SET Table1.target_column = Table2.source_column
WHERE Table1.ID = Table2.ID;
-- MySQL says: No "FROM," no problem. Just commas for me, please!


PostgreSQL brings its own bowl to the table:

UPDATE Table1
SET target_column = Table2.source_column
FROM Table2
WHERE Table1.ID = Table2.ID;
-- PostgreSQL says: I am the 'FROM' runner!


Escaping the SQL Pitfall Dungeon

While embarking on updating tables, sidestep these common booby traps:

• The Double Agent: Watch out for duplicates! Multiple rows in Table2 with the same ID can ambush your updates.
• Null's Stealth: If untreated, NULLs can silently wipe your data. Beware!
• The Shapeshifter: Confirm target_column and source_column have the same data type, or deal with some transformation terrors.

The MERGE Magic Wand

For heavy lifting, the MERGE command comes handy, updating, inserting, and even vanishing rows in just one wave:

MERGE INTO Table1 USING Table2
ON Table1.ID = Table2.ID
WHEN MATCHED THEN
    UPDATE SET Table1.target_column = Table2.source_column;
-- Merge says: When matched, do magic! Otherwise, poof! Options you have.


This spell ensures that the update happens only on a match. And if it's a mismatch, you still have options!

Guardian of Data Integrity

Protect your database kingdom with these steps:

1. Stand Guard with Transactions: Guard your update statement with a transaction, committing only after successful validation.
2. The Inspection Round: Measure twice. Verify the row counts and data samples pre and post updates.
3. The Safety Vault: Always keep a backup. You never know when you might need it!