Sql updating multiple rows from another table

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In this article I will demonstrate a fast way to update rows in a large table Consider a table called which has more than 5 millions rows.Suppose you want to update a column with the value 0, if it that column contains negative value.In addition, my related problem was that only some of the columns were modified and many rows had no edits to these columns, so I wanted to leave those alone - basically restore a subset of columns from a backup of the entire table.If you want to just restore all rows, skip the where clause.But since the UPDATE has no WHERE clause, it will update all rows, even those where the subquery returns NULL.Consequently, to prevent this, you might do this: One potential issue may arise when the subquery actually finds more than one matching row in tbl B.

Many a times, you come across a requirement to update a large table in SQL Server that has millions of rows (say more than 5 millions) in it.UPDATE Table1 T1 SET T1= (SELECT T2FROM Table2 T2 WHERE T2= T1.id), T1= (SELECT T2FROM Table2 T2 WHERE T2= T1.id) WHERE T1IN (SELECT T2FROM Table2 T2 WHERE T2= T1.id); The full example is here: beef is in having the columns that you want to use as the key in parentheses in the where clause before 'in' and have the select statement with the same column names in parentheses.where (column1,column2) in ( If your table t1 and it's backup t2 have many columns, here's a compact way to do it.I have a SQL query where I am trying to update a column in a table (tbl A) from data in another table (tbl B).This works fine when I try to update all the records in tbl A, however, in this case I only have missing data which I have identified and populated in tbl B.

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