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Oddly, this is valid.
select * from (select * from t1) as ``;
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The SQL standard (2016) states this
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Syntax Rules
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1) An <identifier start> is any character in the Unicode General Category classes “Lu”, “Ll”, “Lt”, “Lm”,“Lo”, or “Nl”.
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NOTE 126 — The Unicode General Category classes “Lu”, “Ll”, “Lt”, “Lm”, “Lo”, and “Nl” are assigned to Unicode
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characters that are, respectively, upper-case letters, lower-case letters, title-case letters, modifier letters, other letters, and
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letter numbers.
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further https://mariadb.com/kb/en/identifier-names/ states
_Identifiers are not permitted to contain the ASCII NUL character (U+0000) and supplementary characters (U+10000 and higher). _
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