SQL Server Multi-table connection update

One, MS SQL Server Multi-Table Association update

SQL Server provides the FROM clause of the update, which connects the table that will be updated to its data source. Although only one table can be updated, it is possible to reference data other than the table to be updated in an update expression by connecting the table that will be updated with its data source.
General form:

Update A SET field 1=b table field expression, fields 2=b table segment expression from B WHERE logical expression

For example:

UPDATE dbo. Table2
SET dbo. Table2.colb = dbo. Table2.colb + dbo. Table1.colb
FROM dbo. Table2
INNER JOIN dbo. Table1
On (dbo. Table2.cola = dbo. Table1.cola);


The actual update is performed on the table to be updated, not on the new result set formed by the FROM clause

SQL Server Multi-table connection update