Run CHECKSUM TABLE command against a table.
There is a caveat for this. According to the MySQL Documentation on CHECKSUM TABLE:
If the checksums for two tables are different, then it is almost
certain that the tables are different in some way. However, because
the hashing function used by CHECKSUM TABLE is not guaranteed to be
collision-free, there is a slight chance that two tables which are not
identical can produce the same checksum.
CHECKSUM TABLE is 99.99%, not 100%.
How can you aggressively check all the items of a table for matches and mismatches? You can actually run a great tool from Percona Tools called pt-table-sync. It will check for differences in tables between Master and Slave, as long as the table structure is identical.
For example, to sync the table
db.tb1 on a Slave in relation to its Master, run
pt-table-sync as follows:
pt-table-sync --print --sync-to-master h=SlaveIP,D=db,t=tbl > SQLtoFixDifferences.sql
When you run this, the table
db.tb1 on the Slave is compared to that of its Master using the Primary Key (or Unique Key is there is no Primary Key) of the Slave's
db.tb1. The output will be a series of SQL commands, usually
REPLACE INTO and
DELETE FROM. The script
SQLtoFixDifferences.sql is to be executed on the Slave. When done, the data in
db.tb1 should be identical to its counterpart on the Master.
To test it then, run these commands:
CHECKSUM TABLE db.tb1;
SELECT COUNT(1) FROM db.tb1;
The results should be identical on Master and Slave.
I have never used pt-table-sync. I have been using mk-table-sync (MAATKIT tool from Percona) for years and I know it has always worked for me. I fully trust Percona's pt-table-sync is at the least the same, if not superior, quality.