Get records from previous day to today

Question

hi
i have 1 main table, table A, which has all the data .
now i have table b which has previous day data and table c which has current data. i need to compare table a(each column)
to each column in table b and c
and need to find out rows that has been changed from yesterday to today and send that data.
table B and table C doesnt have any date which say which date it got changed

Answer 1

>> I have 1 main table, table A, which has all the data .<<
What is a “main table”? I never used or heard that term. I am old, so I remember “main” or “master” tape files, however. 
No table should have all the data in a schema that has more than one relationship in it. Where is the DDL?  
>> now I have table b which has previous day data and table c which has current data <<
NO! This design error is called “Attribute splitting” and it usually comes from programmers like you who are using SQL to write 1950's magnetic tape files. Would you have a “Male_Personnel” and a “Female_Personnel”  table or a “Personnel” table? Those
two absurd tables were split on sex_code, just like you want to split this unknown data on a “<something>_date” attribute. 
>>  I need to compare table a(each column) to each column in table b and c and need to find out rows that has been changed from yesterday to today and send that data. <<
No, you need to stop trying to write SQL until you know what you are doing. To track the history of, say, Foobars we need to see time as a continuum and model it as (begin_date, end_date) pairs that define when a foobar had a particular value. Here is the skeleton. 
CREATE TABLE Foobar_History 
(foo_id CHAR(9) NOT NULL, 
 start_date DATE NOT NULL, 
 end_date DATE, --null means current 
 CHECK (start_date <= end_date),
 foo_status INTEGER NOT NULL, 
 PRIMARY KEY (foo_id, start_date)); 
When the end_date is NULL, that state of being is still current. You use a simple query for the status on any particular date;
SELECT * 
  FROM Foobar
 WHERE @in_cal_date
     BETWEEN start_date
      AND COALESCE (end_date, CURRENT_TIMESTAMP);
There are more tricks in the DDL to prevent gaps, etc
CREATE TABLE Events
(event_id CHAR(10) NOT NULL,
 previous_event_end_date DATE NOT NULL  
 CONSTRAINT Chained_Dates  
  REFERENCES Events (event_end_date), 
 event_start_date DATE NOT NULL, 
 event_end_date DATE UNIQUE, -- null means event in progress
  PRIMARY KEY (event_id, event_start_date), 
 CONSTRAINT Event_Order_Valid 
  CHECK (event_start_date <= event_end_date), 
 CONSTRAINT Chained_Dates 
  CHECK (DATEADD(DAY, 1, previous_event_end_date) = event_start_date)
-- CHECK (previous_event_end_date + INTERVAL '01' DAYS) = event_start_date)
-- disable the Chained_Dates constraint
ALTER TABLE Events NOCHECK CONSTRAINT Chained_Dates;
GO
-- insert a starter row
INSERT INTO Events(event_id, previous_event_end_date, event_start_date, event_end_date)
VALUES ('Foo Fest', '2010-01-01', '2010-01-02', '2010-01-05');
GO
-- enable the constraint in the table
ALTER TABLE Events CHECK CONSTRAINT Chained_Dates;
GO
-- this works
INSERT INTO Events(event_id, previous_event_end_date, event_start_date, event_end_date)
VALUES ('Glob Week', '2010-01-05', '2010-01-06', '2010-01-10');
-- this fails
INSERT INTO Events(event_id, previous_event_end_date, event_start_date, event_end_date)
VALUES ('Snoob', '2010-01-09', '2010-01-11', '2010-01-15');  
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