ClickHouse/docs/en/query_language/functions/conditional_functions.md

Conditional functions

if(cond, then, else), cond ? operator then : else

Returns then if cond != 0, or else if cond = 0. cond must be of type UInt8, and then and else must have the lowest common type.

then and else can be NULL

multiIf

Allows you to write the CASE operator more compactly in the query.

multiIf(cond_1, then_1, cond_2, then_2...else)

Parameters:

• cond_N — The condition for the function to return then_N.
• then_N — The result of the function when executed.
• else — The result of the function if none of the conditions is met.

The function accepts 2N+1 parameters.

Returned values

The function returns one of the values then_N or else, depending on the conditions cond_N.

Example

Take the table

┌─x─┬────y─┐
│ 1 │ ᴺᵁᴸᴸ │
│ 2 │    3 │
└───┴──────┘

Run the query SELECT multiIf(isNull(y) x, y < 3, y, NULL) FROM t_null. Result:

┌─multiIf(isNull(y), x, less(y, 3), y, NULL)─┐
│                                          1 │
│                                       ᴺᵁᴸᴸ │
└────────────────────────────────────────────┘