How to Update SQL Table Rows Based on Matching Usernames?

Update the row value in the table based on the matching username

Q: Update table value

In SQL Database, you have two tables, table_a and table_b, both of which have a common column called user_name. You want to copy specific columns (named column_b_1 and column_b_2) in table_b to corresponding columns (column_a_1 and column_a_2) in table_a based on matching user_name values. How can I achieve this using SQL statements?

Answer: Solution

If the appropriate indexes are in place, you can use the following UPDATE statement:

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

Note: This UPDATE statement uses a subquery to retrieve the column values ​​from table_b that correspond to each row in table_a that has a matching user_name.

If performance is a concern, consider using SELECT and JOIN operations to build a temporary table to store the modified rows. You can then delete the existing data from table_a and repopulate it from the temporary table.

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