Updating a table from a join
When you look at this it looks very simple but when we try to think the solution, I have seen developers coming up with many different solutions for example sometime they write cursor, table variables, local variables etc. Col2)) UPDATE CTE SET Col1 = _Col1, Col2 = _Col2from stackoverflow.“UPDATE Table1 SET Col2 = t2.
However, the easiest and the most clean way is to use JOIN clause in the UPDATE statement and use multiple tables in the UPDATE statement and do the task.
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Using UPDATE STATISTICS WITH FULLSCAN will scan the entire table.
set (col1,col7,col8) = (select -1, col7,col8 from tab b where a.col2 = b.col2 and a.col3 = b.col3 and a.col3 = b.col4 ) Don" id="ctl00_m_m_i_ctl00_gr_ctl05_bestanswerbody" class="textarea-bestanswerhidden" name="bestanswerbody" answerbody Id="5190407" / Method 1: update tab a set col1 = -1 where exists (select 1 from tab b where a.col2 = b.col2 and a.col3 = b.col3 and a.col3 = b.col4 ) Method 2: update tab a set (col1,col7,col8) = (select -1, col7,col8 from tab b where a.col2 = b.col2 and a.col3 = b.col3 and a.col3 = b.col4 ) where exists (select 1 from tab b where a.col2 = b.col2 and a.col3 = b.col3 and a.col3 = b.col4 ) Note: In Method 2 the sub-query must return only 1 row.
Using the INDEX option will update index statistics only.
2) By default, the UPDATE STATISTICS statement uses only a sample of records of the table.
In recent times I have seen a developer writing a cursor to update a table. We want to update the value from Table2 to Table1 for the rows where Col1 is 21 and 31. I resolved this by providing the alias name after update query:: UPDATE Table1 SET Col2 = t2.
When asked the reason was he had no idea how to use multiple tables with the help of the JOIN clause in the UPDATE statement. Additionally, we want to update the values of Col2 and Col3 only.
Search for updating a table from a join:
1) By default, the UPDATE STATISTICS statement updates both index and column statistics.