About naming fields
Field names must be unique, and can contain up to 100 characters. Follow these guidelines when naming fields:
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,(comma), +, -, *, /, ^, &, =, , >, <, ( ), [ ], { }, ", ; (semicolon), : (colon), :: (relational indicator), $ (variable indicator)
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If you're using ODBC or JDBC to share FileMaker Pro data, avoid using SQL keywords in field names.
Related topics 
Using a reserved word or symbol for a field or table name
Changing field names