# `sync-diff-inspector` Restrictions

+ Online check is not supported for data migration between `MySQL` and `TiDB`
+ In `TiDB` and `MySQL`, `FLOAT`, `DOUBLE` and other floating-point types are implemented differently, set **`ignore-columns`** in `Table Config` to skip checking these columns
+ Support checking tables that do not supply the primary key or the unique index, as a result, no uniqueness guarantee for such table rows during checking

+ Note that `JSON` type is supported from TiDB version 6.5.
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Online check is not supported for data migration between `MySQL` and `TiDB`. Ensure that no data is written into the upstream-downstream checklist, and that data in a certain range is not changed. You can check data in this range by setting range.

In `TiDB` and `MySQL`, `FLOAT`, `DOUBLE`and other `floating-point` types are implemented differently. `FLOAT` and `DOUBLE `respectively take 6 and 15 significant digits for calculating checksum. If you do not want to use this feature, set `ignore-columns` to skip checking these columns.

Support checking tables that do not supply the primary key or the unique index. However, if data is inconsistent, the generated SQL statements might not be able to repair the data correctly.

We will talk about `Table Config` later.