Conditional update on Hana Studio (SQL Script) trigger

问题

I have two example tables:

    TABLE1:
      ID    | COLUMN_B| COLUMN_C
   _________|_________|_________
       1    |    0    |    1
    ________|_________|_________
       2    |    0    |    1
    ________|_________|_________
       3    |    0    |    1


    TABLE2:
      ID    | COLUMN_E| COLUMN_F
    ________|_________|________
       1    |    Y    |    X
    ________|_________|_________
       2    |    Y    |    X
    ________|_________|_________
       3    |    Y    |    X

What I would like to do is to write a trigger on Hana Studio using SQL Script to update column E from table 2 when column B from table 1 is updated to a specific value (let's say, 100). Rows from table 1 are referenced in table 2 with the first column (ID).

I wrote the following code:

create trigger "UPDATE_TABLES"
    after update of "COLUMN_B" on "TABLE1"
    referencing new row as new, old row as old
    for each row 
begin
    update "TABLE2"
    set "COLUMN_E" = 'my new value'
    where :old."COLUMN_B" = '100' and "TABLE1"."ID" = :old."ID";
end;

When I set TABLE1.COLUMN_B on row 1 to 100, I expect the code to change TABLE2.COLUMN_E to "my new value" on row 1, but nothing happens. Could anyone point what exactly I am doing wrong here?

回答1:

I guess the UPDATE statement in the trigger code should be slighly different as follows

create trigger "UPDATE_TABLES"
    after update of "COLUMN_B" on "TABLE1"
    referencing new row as new, old row as old
    for each row 
begin
    update "TABLE2"
    set "COLUMN_E" = 'my new value'
    where :new."COLUMN_B" = '100' 
    and TABLE2.ID = :old."ID";
end;

Otherwise, I get syntax error while creating the trigger Could you please verify?

回答2:

Rookie mistake. I wanted the column_e value to change on changes on values from column_b, but I was actually tracking the old values from column_b. Corrected it to:

create trigger "UPDATE_TABLES"
    after update of "COLUMN_B" on "TABLE1"
    referencing new row as new, old row as old
    for each row 
begin
    update "TABLE2"
    set "COLUMN_E" = 'my new value'
    where :new."COLUMN_B" = '100' and "TABLE1"."ID" = :old."ID";
end;

and it worked!

来源：https://stackoverflow.com/questions/52297810/conditional-update-on-hana-studio-sql-script-trigger