How to delete rows from table based on another table

[Sas_noob25]

I have a problem I'm trying to solve, and not really sure where to start. 

I have two tables Table A and Table B. I'm trying to delete ALL of the customer IDs from Table A if they appear in Table B, but Table A sometimes has multiple entries for the same customer ID. My end result should be Table A with only records that are not in Table B.

Example:

Table A

Customer ID	Date
A	5/7/2020
A	5/11/2020
B	5/8/2020
B	5/9/2020
B	5/10/2020
C	5/11/2020

Table B

Customer ID	Delete Flag
B	Y
B	Y
A	Y

In this example I would only want Customer ID C to show up in my final table.

I have a few thousand rows of data in Table A that I'm checking against. Any help is greatly appreciated!

[svh · Accepted solution]

This is relatively straightforward with a subquery like this:

(I have altered the name of the variable "Customer ID". It can work as a named literal like this: 'Customer ID'n

proc sql;
   create table want as
   select * from A
  where customer_ID not in (select customer_ID from B);
quit;

[Sas_noob25]

Thank you! Super easy way to do this, not sure how I didn't think of this.

[Kurt_Bremser]

If data size and performance is an issue, use a hash object:

data want;
set a;
if _n_ 01
then do;
  declare hash b (dataset:"b");
  b.definekey("customer_id");
  b.definedone();
end;
if b.check() ne 0;
run;

[Reeza]

proc sort data=tableB out=b_unique nodupkey;
by customerID;
run;

proc sort data=tableA;
by customerID;

data tableC;
merge tableA(in=ina) b_unique(in=inb drop=deleteflag);
by customerID;
if not inb;
run;

A SQL way that will delete records from the table - test thoroughly before using something like this:

data tableA;
infile cards dlm='09'x;
input CustomerID  $	Date : ddmmyy10.;
format date date9.;
cards;
A	5/7/2020
A	5/11/2020
B	5/8/2020
B	5/9/2020
B	5/10/2020
C	5/11/2020
;;;;
run;

data tableB;
infile cards dlm='09'x;
input CustomerID $	DeleteFlag $;
cards;
B	Y
B	Y
A	Y
;;;;
run;

proc sql;
delete * from tableA where customerID  in (select distinct(CustomerID) from TableB);
quit;

[Sas_noob25]

Thank you!

This step below worked as well.

proc sort data=tableB out=b_unique nodupkey;
by customerID;
run;

proc sort data=tableA;
by customerID;

data tableC;
merge tableA(in=ina) b_unique(in=inb drop=deleteflag);
by customerID;
if not inb;
run;