Question

I have two similar tables table_a and table_b
table_a is my current data and I need to update this info using table_b which is a temporary table. The only difference between the two is table_a has a password field that table_b will not have.

I am trying to do a couple of things.

1.Compare the data based on the "user_id" field. 
2. If there is a user_id not found in table_b but there is one in table_a remove that row in table_a
3. If there is a user_id in table_b that is not found in table_a add that row of data to table_a
4. If the user_id is found in both then check two of the fields "email" and "job_code" and make sure they are both whatever table_b says.

Should I do this in separate MySQL statements in the order I have numbered above? below is my try at the above statements. Any help or troubleshoot is greatly appreciated. Thanks!

Statement 1:

SELECT * FROM table_a
WHERE table_a.user_id
NOT IN (
SELECT table_b.user_id
FROM table_b
WHERE table_a.user_id=table_b.user_id
)  // But how do I delete those records that are selected?

Statement 2:

SELECT * FROM table_b
WHERE table_b.user_id
NOT IN (
SELECT table_a.user_id
FROM table_a
WHERE table_a.user_id=table_b.user_id
) //How do I Insert these records that I have in table_b but not in table_a

Statement 3:

SELECT email FROM table_b
WHERE table_b.user_id = table_a.user_id,
AND table_b.email != table_a.email  //now I need to update table_a with the emails from table_b

Answer 1

Statement #1

DELETE A.*
FROM table_a A
LEFT JOIN table_b B
USING (user_id)
WHERE B.user_id IS NULL;

Statement #2

INSERT INTO table_b (column1,column2,...,columnN)
SELECT A.column1,A.column2,...,A.columnN
FROM table_b B LEFT JOIN table_a A
USING (user_id)
WHERE A.user_id IS NULL;

Statement #3

UPDATE table_a A INNER JOIN table_b B USING (user_id)
SET A.email = B.email,A.job_code = B.job_code;

UPDATE 2012-06-19 11:54 EDT

A and B are just aliases for the table.

For example, the query of Statement #3 could have been written like the following:

UPDATE table_a as A INNER JOIN table_b as B USING (user_id)
SET A.email = B.email,A.job_code = B.job_code;

or with no aliases whatsoever, like this:

UPDATE table_a INNER JOIN table_b USING (user_id)
SET table_a.email = table_b.email,table_a.job_code = table_b.job_code;