ClickHouse/doc/reference/en/functions/conditional_functions.rst

Conditional functions
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if(cond, then, else), оператор cond ? then : else
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Returns 'then' if 'cond != 0', or 'else' if 'cond = 0'.
'cond' must be UInt 8, and 'then' and 'else' must be a type that has the smallest common type.