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This query erroneously returns NULL:
SELECT UNHEX(CONCAT('414c2', HEX(8+ROUND(RAND()*7)),SUBSTR(SHA(''),6,7),HEX(2+ROUND(RAND())*8)));
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If I remove HEX, it correctly returns a string in hexadecimal format:
SELECT CONCAT('414c2', HEX(8+ROUND(RAND()*7)),SUBSTR(SHA(''),6,7),HEX(2+ROUND(RAND())*8));
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+------------------------------------------------------------------------------------+
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| CONCAT('414c2', HEX(8+ROUND(RAND()*7)),SUBSTR(SHA(''),6,7),HEX(2+ROUND(RAND())*8)) |
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+------------------------------------------------------------------------------------+
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| 414c2B3ee5e6bA |
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+------------------------------------------------------------------------------------+
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If I now add a user variable assignment, it erroneously returns a broken hexadecimal string:
SELECT @a:=CONCAT('414c2', HEX(8+ROUND(RAND()*7)),SUBSTR(SHA(''),6,7),HEX(2+ROUND(RAND())*8));
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+----------------------------------------------------------------------------------------+
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| @a:=CONCAT('414c2', HEX(8+ROUND(RAND()*7)),SUBSTR(SHA(''),6,7),HEX(2+ROUND(RAND())*8)) |
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+----------------------------------------------------------------------------------------+
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| 414c299 ee56b2 |
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+----------------------------------------------------------------------------------------+
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The same problem is reproducible in a simplified query:
SELECT @a:=CONCAT('2', '2', SUBSTR(SHA(''),6,7));
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+-------------------------------------------+
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| @a:=CONCAT('2', '2', SUBSTR(SHA(''),6,7)) |
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+-------------------------------------------+
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| 223ee5 6b |
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+-------------------------------------------+
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