ClickHouse/docs/en/sql_reference/functions/in_functions.md

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60	Implementing the IN Operator

Functions For Implementing the IN Operator

in, notIn, globalIn, globalNotIn

See the section IN operators.

tuple(x, y, …), operator (x, y, …)

A function that allows grouping multiple columns. For columns with the types T1, T2, …, it returns a Tuple(T1, T2, …) type tuple containing these columns. There is no cost to execute the function. Tuples are normally used as intermediate values for an argument of IN operators, or for creating a list of formal parameters of lambda functions. Tuples can’t be written to a table.

tupleElement(tuple, n), operator x.N

A function that allows getting a column from a tuple. ‘N’ is the column index, starting from 1. N must be a constant. ‘N’ must be a constant. ‘N’ must be a strict postive integer no greater than the size of the tuple. There is no cost to execute the function.

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