update one table with data from another table

This blog post illustrates how to update more than one column in a table with values from columns in another table and explains how to do it in two RDBMS that I use.

Table Structures and values:
TableA has four columns: a, b, c, d (a is the primary key column)
TableB has five columns: a1, b1, c1, d1, e1 (a1 and b1 together constitute the primary key for this table)
The foreign key relationship between the two tables is based on A.a = B.a1
The data in these 2 tables is as follows:
I. TableA
a b c d
1 x y z
2 a b c
3 t x z

II. TableB
a1 b1 c1 d1 e1
1 x1 y1 z1 40
2 a1 b1 c1 50

The requirement is to write a SQL to update columns b, c and d in TableA from the columns b1, c1 and d1 from TableB where-ever the join condition satisfies and e1 > 40 in TABLEB.

Oracle:
UPDATE TABLEASET (b, c, d) = (SELECT b1, c1, d1 from TABLEB WHERE TABLEB.a1 = TABLEA.a and TABLEB.e1 > 40)WHERE EXISTS (SELECT 1 from TABLEB WHERE TABLEB.a1 = TABLEA.a and TABLEB.e1 > 40)
/

Results after the update:
a b c d
————————————
1 x y z
2 a1 b1 c1
3 t x z


SQL Server:
UPDATE TABLEA
SET b = TABLEB.b1,
c = TABLEB.c1,
d = TABLEB.d1
FROM TABLEA, TABLEB
WHERE TABLEA.a = TABLEB.a1
AND TABLEB.e1 > 40
GO

Note: This is an extension in SQL Server i.e. the FROM clause – it does make it simple to understand and is a nice feature.
Results after the update:
a b c d
————————————
1 x y z
2 a1 b1 c1
3 t x z



Happy writing SQL