ClickHouse/docs/en/query_language/operators.md

# Operators

All operators are transformed to the corresponding functions at the query parsing stage, in accordance with their precedence and associativity.
Groups of operators are listed in order of priority (the higher it is in the list, the earlier the operator is connected to its arguments).

## Access Operators

`a[N]` Access to an element of an array; ` arrayElement(a, N) function`.

`a.N` – Access to a tuble element; `tupleElement(a, N)` function.

## Numeric Negation Operator

`-a`  – The `negate (a)` function.

## Multiplication and Division Operators

`a * b`  – The `multiply (a, b) function.`

`a / b`  – The ` divide(a, b) function.`

`a % b` – The `modulo(a, b) function.`

## Addition and Subtraction Operators

`a + b` – The `plus(a, b) function.`

`a - b`  – The `minus(a, b) function.`

## Comparison Operators

`a = b` – The `equals(a, b) function.`

`a == b` – The ` equals(a, b) function.`

`a != b` – The `notEquals(a, b) function.`

`a <> b` – The `notEquals(a, b) function.`

`a <= b` – The `lessOrEquals(a, b) function.`

`a >= b` – The `greaterOrEquals(a, b) function.`

`a < b` – The `less(a, b) function.`

`a > b` – The `greater(a, b) function.`

`a LIKE s` – The `like(a, b) function.`

`a NOT LIKE s` – The `notLike(a, b) function.`

`a BETWEEN b AND c` – The same as `a >= b AND a <= c.`

`a NOT BETWEEN b AND c` – The same as `a < b OR a > c.`

## Operators for Working With Data Sets

*See the section [IN operators](select.md#select-in-operators).*

`a IN ...` – The `in(a, b) function`

`a NOT IN ...` – The `notIn(a, b) function.`

`a GLOBAL IN ...` – The `globalIn(a, b) function.`

`a GLOBAL NOT IN ...` – The `globalNotIn(a, b) function.`

## Operator for Working With Dates and Times

``` sql
EXTRACT(part FROM date);
```

Extracts a part from a given date. For example, you can retrieve a month from a given date, or a second from a time.

The `part` parameter specifies which part of the date to retrieve. The following values are available:

- `DAY` — The day of the month. Possible values: 1–31.
- `MONTH` — The number of a month. Possible values: 1–12.
- `YEAR` — The year.
- `SECOND` — The second. Possible values: 0–59.
- `MINUTE` — The minute. Possible values: 0–59.
- `HOUR` — The hour. Possible values: 0–23.

The `part` parameter is case-insensitive.

The `date` parameter specifies the date or the time to process. Either [Date](../data_types/date.md) or [DateTime](../data_types/datetime.md) type is supported.

Examples:

``` sql
SELECT EXTRACT(DAY FROM toDate('2017-06-15'));
SELECT EXTRACT(MONTH FROM toDate('2017-06-15'));
SELECT EXTRACT(YEAR FROM toDate('2017-06-15'));
```

In the following example we create a table and insert into it a value with the `DateTime` type. 

``` sql
CREATE TABLE test.Orders
(
    OrderId UInt64, 
    OrderName String, 
    OrderDate DateTime
)
ENGINE = Log;
```

``` sql
INSERT INTO test.Orders VALUES (1, 'Jarlsberg Cheese', toDateTime('2008-10-11 13:23:44'));
```
``` sql
SELECT 
    toYear(OrderDate) AS OrderYear, 
    toMonth(OrderDate) AS OrderMonth, 
    toDayOfMonth(OrderDate) AS OrderDay, 
    toHour(OrderDate) AS OrderHour, 
    toMinute(OrderDate) AS OrderMinute,
    toSecond(OrderDate) AS OrderSecond
FROM test.Orders;

┌─OrderYear─┬─OrderMonth─┬─OrderDay─┬─OrderHour─┬─OrderMinute─┬─OrderSecond─┐
│      2008 │         10 │       11 │        13 │          23 │          44 │
└───────────┴────────────┴──────────┴───────────┴─────────────┴─────────────┘
```

You can see more examples in [tests](https://github.com/yandex/ClickHouse/blob/master/dbms/tests/queries/0_stateless/00619_extract.sql).

## Logical Negation Operator

`NOT a` The `not(a) function.`

## Logical AND Operator

`a AND b` – The`and(a, b) function.`

## Logical OR Operator

`a OR b` – The `or(a, b) function.`

## Conditional Operator

`a ? b : c` – The `if(a, b, c) function.`

Note:

The conditional operator calculates the values of b and c, then checks whether condition a is met, and then returns the corresponding value. If `b` or `C` is an [arrayJoin()](functions/array_join.md#functions_arrayjoin) function, each row will be replicated regardless of the "a" condition.

## Conditional Expression {#operator_case}

``` sql
CASE [x]
    WHEN a THEN b
    [WHEN ... THEN ...]
    [ELSE c]
END
```

If `x` is specified, then `transform(x, [a, ...], [b, ...], c)` function is used. Otherwise – `multiIf(a, b, ..., c)`.

If there is no `ELSE c` clause in the expression, the default value is `NULL`.

The `transform` function does not work with `NULL`.

## Concatenation Operator

`s1 || s2` – The `concat(s1, s2) function.`

## Lambda Creation Operator

`x -> expr` – The `lambda(x, expr) function.`

The following operators do not have a priority, since they are brackets:

## Array Creation Operator

`[x1, ...]` – The `array(x1, ...) function.`

## Tuple Creation Operator

`(x1, x2, ...)` – The `tuple(x2, x2, ...) function.`

## Associativity

All binary operators have left associativity. For example, `1 + 2 + 3` is transformed to `plus(plus(1, 2), 3)`.
Sometimes this doesn't work the way you expect. For example, ` SELECT 4 > 2 > 3` will result in 0.

For efficiency, the `and` and `or` functions accept any number of arguments. The corresponding chains of `AND` and `OR` operators are transformed to a single call of these functions.

## Checking for `NULL`

ClickHouse supports the `IS NULL` and `IS NOT NULL` operators.

### IS NULL {#operator-is-null}

- For [Nullable](../data_types/nullable.md) type values, the `IS NULL` operator returns:
    - `1`, if the value is `NULL`.
    - `0` otherwise.
- For other values, the `IS NULL` operator always returns `0`.

```bash
:) SELECT x+100 FROM t_null WHERE y IS NULL

SELECT x + 100
FROM t_null
WHERE isNull(y)

┌─plus(x, 100)─┐
│          101 │
└──────────────┘

1 rows in set. Elapsed: 0.002 sec.
```


### IS NOT NULL

- For [Nullable](../data_types/nullable.md) type values, the `IS NOT NULL` operator returns:
    - `0`, if the value is `NULL`.
    - `1` otherwise.
- For other values, the `IS NOT NULL` operator always returns `1`.

```bash
:) SELECT * FROM t_null WHERE y IS NOT NULL

SELECT *
FROM t_null
WHERE isNotNull(y)

┌─x─┬─y─┐
│ 2 │ 3 │
└───┴───┘

1 rows in set. Elapsed: 0.002 sec.
```

[Original article](https://clickhouse.yandex/docs/en/query_language/operators/) <!--hide-->