How to Update Table A Columns Based on Matching Usernames in Table B?

Updating Table A based on Matching Usernames in Table B

This guide demonstrates how to update columns in table table_a using data from table_b, matching rows based on a common "user_name" column. The goal is to populate column_a_1 and column_a_2 in table_a with values from column_b_1 and column_b_2 in table_b, respectively, for matching usernames.

SQL Solution:

The following SQL statement efficiently achieves this update:

UPDATE table_a
SET
    column_a_1 = (SELECT b.column_b_1 FROM table_b b WHERE b.user_name = table_a.user_name),
    column_a_2 = (SELECT b.column_b_2 FROM table_b b WHERE b.user_name = table_a.user_name)
WHERE
    EXISTS (SELECT 1 FROM table_b b WHERE b.user_name = table_a.user_name);

This query uses subqueries to fetch the appropriate values from table_b and applies them to the corresponding rows in table_a. The EXISTS clause ensures that only rows with matching usernames in both tables are updated, preventing errors if a username exists in table_a but not in table_b. Using aliases (like b for table_b) improves readability.

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