使用两个表进行Redshift表更新

Question

I have a requirement to work on an update. The requirement is to update table 2 using the data from table 1. Please find below sample records from the two tables:

TABLE A    
-----------------
colA | colB | colC
-----------------
 1    AAA      ABC
 2    BBB      DEF
 3    CCC      GHI
 3    CCC      HIJ

TABLE B    
-----------------
colA1 | colB1 | colC1
-----------------
 1     AAA      
 2     BBB
 3     CCC
 3     CCC

I need to update the colC1 with values of ColC. Expected output is shown below

TABLE B    
-----------------
colA1 | colB1 | colC1
-----------------
 1    AAA      ABC
 2    BBB      DEF
 3    CCC      GHI
 3    CCC      HIJ

Do we need to use a cursor for this or a simple update statement like shown below would do?

 Update table B
 set colC1 = table A.colC
 from TABLE A, TABLE B
 where colA1 = colA
 and colB1 = colB;

Answer 1

Your SQL seems perfectly fine.

Cursors are normally used for programmatic access to a database, where the program is stepping through the results one-at-a-time, with the cursor pointing to the 'current record'. That isn't needed in normal SQL update statements.

One thing to note... In Amazon Redshift, using an UDPATE on a row causes the existing row to be marked for deletion and a new row is created. (This is a side-effect of using a columnar database.) If many rows are updated, it means that the disk storage becomes less efficient. It can be improved by occasionally running VACUUM tablename , which will remove the deleted storage.