Updating values in sql
In some databases, such as Postgre SQL, when a FROM clause is present, what essentially happens is that the target table is joined to the tables mentioned in the fromlist, and each output row of the join represents an update operation for the target table.When using FROM, one should ensure that the join produces at most one output row for each row to be modified.Because of this indeterminacy, referencing other tables only within sub-selects is safer, though often harder to read and slower than using a join.  Set the value of column C1 in table T to 1, only in those rows where the value of column C2 is "a".I have a database with account numbers and card numbers.Sebastian covers a technique for this in a recent blog post: sqlity.net/en/2867/update-from-select This will tend to work across almost all DBMS which means learn once, execute everywhere. Col2 AS _Col2 FROM T1 JOIN T2 ON T1= T2/*Where clause added to exclude rows that are the same in both tables Handles NULL values correctly*/ WHERE EXISTS(SELECT T1. I know this is old, but just wanted to say this one worked for me.If that is more important to you than performance you might prefer this answer, especially if your update is a one off to correct some data. My server wont allow FROM to be used in an UPDATE statement. This may be a niche reason to perform an update (for example, mainly used in a procedure), or may be obvious to others, but it should also be stated that you can perform an update-select statement without using join (in case the tables you're updating between have no common field).In other words, a target row shouldn't join to more than one row from the other table(s).
Compound assignment operator: = Add and assign -= Subtract and assign *= Multiply and assign /= Divide and assign %= Modulo and assign &= Bitwise AND and assign ^= Bitwise XOR and assign |= Bitwise OR and assign Returns updated data or expressions based on it as part of the UPDATE operation.
Common table expressions can also be used with the SELECT, INSERT, DELETE, and CREATE VIEW statements.
For more information, see WITH common_table_expression (Transact-SQL). For information about table hints, see Table Hints (Transact-SQL).
Vonki solution below works: UPDATE [Sales_Lead].[dbo].[Sales_Import] SET [Account Number] = Retrieve Account Number. As well as being standard SQL and thus more portable it also will raise an error in the event of there being multiple joined rows on the source side (and thus multiple possible different values to use in the update) rather than having the final result be undeterministic. Don't update a value with the same value, it generates extra logging and unnecessary overhead.
Account Number FROM Retrieve Account Number WHERE [Sales_Lead].[dbo].[Sales_Import]. UPDATE [Sales_Lead].[dbo].[Sales_Import] SET [Account Number] = Retrieve Account Number. See example below - it will only perform the update on 2 records despite linking on 3. Account Number Thank you for your interest in this question.