+
Addition.
If both operands are integers, the result is calculated with BIGINT precision. If either integer is unsigned, the result is also an unsigned integer.
For real or string operands, the operand with the highest precision determines the result precision.
SELECT 3+5; +-----+ | 3+5 | +-----+ | 8 | +-----+
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https://mariadb.com/kb/en/addition-operator/