Map

map

Arranges key:value pairs into Map(key, value) data type.

Syntax

map(key1, value1[, key2, value2, ...])

Arguments

• key — The key part of the pair. String or Integer .

• value — The value part of the pair. String , Integer or Array .

Returned value

• Data structure as key:value pairs.

Type: Map(key, value) .

Examples

Query:

SELECT map('key1', number, 'key2', number * 2) FROM numbers(3);

Result:

┌─map('key1', number, 'key2', multiply(number, 2))─┐

│ {'key1':0,'key2':0}                              │

│ {'key1':1,'key2':2}                              │

│ {'key1':2,'key2':4}                              │

└──────────────────────────────────────────────────┘

Query:

CREATE TABLE table_map (a Map(String, UInt64)) ENGINE = MergeTree() ORDER BY a;

INSERT INTO table_map SELECT map('key1', number, 'key2', number * 2) FROM numbers(3);

SELECT a['key2'] FROM table_map;

Result:

┌─arrayElement(a, 'key2')─┐

│                       0 │

│                       2 │

│                       4 │

└─────────────────────────┘

See Also

• Map(key, value) data type

tuple

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.

The function implements the operator (x, y, …) .

Syntax

tuple(x, y, …)

tupleElement

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.

The function implements the operator x.N .

Syntax

tupleElement(tuple, n)