6.8 KiB
| toc_priority | toc_title |
|---|---|
| 46 | Working with maps |
Functions for maps
map
Arranges key:value pairs into a JSON data structure.
Syntax
map(key1, value1[, key2, value2, ...])
Parameters
key— The key part of the pair. String or Integer.value— The value part of the pair. String, Integer or Array.
Returned value
- JSON with
key:valuepairs.
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
mapAdd
Collect all the keys and sum corresponding values.
Syntax
mapAdd(Tuple(Array, Array), Tuple(Array, Array) [, ...])
Parameters
Arguments are tuples of two arrays, where items in the first array represent keys, and the second array contains values for the each key. All key arrays should have same type, and all value arrays should contain items which are promote to the one type (Int64, UInt64 or Float64). The common promoted type is used as a type for the result array.
Returned value
- Returns one tuple, where the first array contains the sorted keys and the second array contains values.
Example
Query:
SELECT mapAdd(([toUInt8(1), 2], [1, 1]), ([toUInt8(1), 2], [1, 1])) as res, toTypeName(res) as type;
Result:
┌─res───────────┬─type───────────────────────────────┐
│ ([1,2],[2,2]) │ Tuple(Array(UInt8), Array(UInt64)) │
└───────────────┴────────────────────────────────────┘
mapSubtract
Collect all the keys and subtract corresponding values.
Syntax
mapSubtract(Tuple(Array, Array), Tuple(Array, Array) [, ...])
Parameters
Arguments are tuples of two arrays, where items in the first array represent keys, and the second array contains values for the each key. All key arrays should have same type, and all value arrays should contain items which are promote to the one type (Int64, UInt64 or Float64). The common promoted type is used as a type for the result array.
Returned value
- Returns one tuple, where the first array contains the sorted keys and the second array contains values.
Example
Query:
SELECT mapSubtract(([toUInt8(1), 2], [toInt32(1), 1]), ([toUInt8(1), 2], [toInt32(2), 1])) as res, toTypeName(res) as type;
Result:
┌─res────────────┬─type──────────────────────────────┐
│ ([1,2],[-1,0]) │ Tuple(Array(UInt8), Array(Int64)) │
└────────────────┴───────────────────────────────────┘
mapPopulateSeries
Fills missing keys in the maps (key and value array pair), where keys are integers. Also, it supports specifying the max key, which is used to extend the keys array.
Syntax
mapPopulateSeries(keys, values[, max])
Generates a map, where keys are a series of numbers, from minimum to maximum keys (or max argument if it specified) taken from keys array with a step size of one, and corresponding values taken from values array. If the value is not specified for the key, then it uses the default value in the resulting map. For repeated keys, only the first value (in order of appearing) gets associated with the key.
The number of elements in keys and values must be the same for each row.
Parameters
Returned value
Example
Query:
select mapPopulateSeries([1,2,4], [11,22,44], 5) as res, toTypeName(res) as type;
Result:
┌─res──────────────────────────┬─type──────────────────────────────┐
│ ([1,2,3,4,5],[11,22,0,44,0]) │ Tuple(Array(UInt8), Array(UInt8)) │
└──────────────────────────────┴───────────────────────────────────┘