Mysql – Finding missing records from two tables

This should do the trick for you:

DELIMITER $$
DROP TRIGGER IF EXISTS `employee_INSERT` $$
CREATE TRIGGER `employee_INSERT` 
AFTER INSERT ON `employee`
FOR EACH ROW
BEGIN
    INSERT INTO employee_tools (Id, Tool)
    SELECT new.Id, tools.Tool_Name 
            FROM tools
            WHERE tools.Division = new.Division;
END $$
DELIMITER ;

So, your approach is good in my opinion, with little tweaks:

First, when you create the temp table, or when you are generating the hash value, use DATE function (You mentioned is but not sure you're using it in the query):

SELECT ...., crc32(CONCAT(column1, DATE(column10))),

so you don't have to deal with 'fuzziness' [Assuming that you want the preciseness to be at day level]

To get the records that exist in one table, and not the other:

SELECT applicationtable.id, applicationtable.column1 
FROM applicationtable 
LEFT JOIN backendtable USING (id, column1) 
WHERE backendtable.id IS NULL [AND backendtable.column1 IS NULL]
UNION
SELECT backendtable.id, backendtable.column1 
FROM backendtable 
LEFT JOIN applicationtable USING (id, column1) 
WHERE applicationtable.id IS NULL [AND applicationtable.column1 IS NULL]

To get the records that have different values for the same PK:

SELECT applicationtable.id, applicationtable.column1 
FROM applicationtable 
INNER JOIN backendtable USING (id, column1) 
WHERE applicationtable.crc32_value <> backendtable.crc32_value

Be careful though:

• If NULL value is allowed in column2 or in column10, CRC32 would give the same "null", even if the second field has a value, and this will not be reported by the query as "NULL <> NULL"
• It is very unlikely to get collided CRC32 values, but it is not impossible. MD5 would be an option, but more expensive one.
• Having [AND backendtable.column1 IS NULL] in the WHERE clause is not necessary if the field is defined to be NOT NULL