Steps to reproduce:

Precondition: MySQL database

1. Import the host: mysql_lld_master.yaml (Note: this import file is for 8.0 version)
2. Start the server, and execute the LLD
3. Check the discovered items, for example, discovered script item:

      SELECT LENGTH(params), CHAR_LENGTH(params) FROM items WHERE key_='m1.script[a]';

1. Execute the LLD again, and check the server's logs

Result:
On step 2 the items are discovered with no LLD rule error, but params is silently truncated to fit items.params (text, 65535 bytes):

LENGTH(params)  CHAR_LENGTH(params)
65532           16383

LLD update (step #4) - fails with query failed error in the log.

[Z3005] query failed: [1406] Data too long for column 'params' at row 1 [update items set params='return '𝕏.....

Also note, that discovered telemetry query item is broken on the frontend in such scenario. See screenshot:

Note: seems that issue is present for

• Items: params, description, posts, headers, query
• Triggers: description
• Host: macros description, value, SNMP interface parameters

Expected:
A discovered value that doesn't fit its DB field should be rejected during discovery, and LLD rule should display the correct error, why the item was not created.