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238 lines
6.6 KiB
Markdown
238 lines
6.6 KiB
Markdown
# Operators
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All operators are transformed to the corresponding functions at the query parsing stage, in accordance with their precedence and associativity.
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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).
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## Access Operators
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`a[N]` Access to an element of an array; ` arrayElement(a, N) function`.
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`a.N` – Access to a tuble element; `tupleElement(a, N)` function.
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## Numeric Negation Operator
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`-a` – The `negate (a)` function.
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## Multiplication and Division Operators
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`a * b` – The `multiply (a, b) function.`
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`a / b` – The ` divide(a, b) function.`
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`a % b` – The `modulo(a, b) function.`
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## Addition and Subtraction Operators
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`a + b` – The `plus(a, b) function.`
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`a - b` – The `minus(a, b) function.`
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## Comparison Operators
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`a = b` – The `equals(a, b) function.`
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`a == b` – The ` equals(a, b) function.`
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`a != b` – The `notEquals(a, b) function.`
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`a <> b` – The `notEquals(a, b) function.`
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`a <= b` – The `lessOrEquals(a, b) function.`
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`a >= b` – The `greaterOrEquals(a, b) function.`
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`a < b` – The `less(a, b) function.`
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`a > b` – The `greater(a, b) function.`
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`a LIKE s` – The `like(a, b) function.`
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`a NOT LIKE s` – The `notLike(a, b) function.`
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`a BETWEEN b AND c` – The same as `a >= b AND a <= c.`
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`a NOT BETWEEN b AND c` – The same as `a < b OR a > c.`
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## Operators for Working With Data Sets
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*See the section [IN operators](select.md#select-in-operators).*
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`a IN ...` – The `in(a, b) function`
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`a NOT IN ...` – The `notIn(a, b) function.`
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`a GLOBAL IN ...` – The `globalIn(a, b) function.`
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`a GLOBAL NOT IN ...` – The `globalNotIn(a, b) function.`
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## Operator for Working With Dates and Times {#operators-datetime}
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``` sql
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EXTRACT(part FROM date);
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```
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Extracts a part from a given date. For example, you can retrieve a month from a given date, or a second from a time.
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The `part` parameter specifies which part of the date to retrieve. The following values are available:
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- `DAY` — The day of the month. Possible values: 1–31.
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- `MONTH` — The number of a month. Possible values: 1–12.
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- `YEAR` — The year.
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- `SECOND` — The second. Possible values: 0–59.
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- `MINUTE` — The minute. Possible values: 0–59.
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- `HOUR` — The hour. Possible values: 0–23.
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The `part` parameter is case-insensitive.
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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.
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Examples:
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``` sql
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SELECT EXTRACT(DAY FROM toDate('2017-06-15'));
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SELECT EXTRACT(MONTH FROM toDate('2017-06-15'));
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SELECT EXTRACT(YEAR FROM toDate('2017-06-15'));
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```
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In the following example we create a table and insert into it a value with the `DateTime` type.
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``` sql
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CREATE TABLE test.Orders
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(
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OrderId UInt64,
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OrderName String,
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OrderDate DateTime
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)
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ENGINE = Log;
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```
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``` sql
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INSERT INTO test.Orders VALUES (1, 'Jarlsberg Cheese', toDateTime('2008-10-11 13:23:44'));
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```
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``` sql
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SELECT
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toYear(OrderDate) AS OrderYear,
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toMonth(OrderDate) AS OrderMonth,
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toDayOfMonth(OrderDate) AS OrderDay,
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toHour(OrderDate) AS OrderHour,
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toMinute(OrderDate) AS OrderMinute,
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toSecond(OrderDate) AS OrderSecond
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FROM test.Orders;
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┌─OrderYear─┬─OrderMonth─┬─OrderDay─┬─OrderHour─┬─OrderMinute─┬─OrderSecond─┐
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│ 2008 │ 10 │ 11 │ 13 │ 23 │ 44 │
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└───────────┴────────────┴──────────┴───────────┴─────────────┴─────────────┘
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```
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You can see more examples in [tests](https://github.com/yandex/ClickHouse/blob/master/dbms/tests/queries/0_stateless/00619_extract.sql).
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## Logical Negation Operator
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`NOT a` The `not(a) function.`
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## Logical AND Operator
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`a AND b` – The`and(a, b) function.`
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## Logical OR Operator
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`a OR b` – The `or(a, b) function.`
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## Conditional Operator
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`a ? b : c` – The `if(a, b, c) function.`
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Note:
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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.
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## Conditional Expression {#operator_case}
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``` sql
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CASE [x]
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WHEN a THEN b
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[WHEN ... THEN ...]
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[ELSE c]
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END
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```
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If `x` is specified, then `transform(x, [a, ...], [b, ...], c)` function is used. Otherwise – `multiIf(a, b, ..., c)`.
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If there is no `ELSE c` clause in the expression, the default value is `NULL`.
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The `transform` function does not work with `NULL`.
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## Concatenation Operator
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`s1 || s2` – The `concat(s1, s2) function.`
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## Lambda Creation Operator
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`x -> expr` – The `lambda(x, expr) function.`
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The following operators do not have a priority, since they are brackets:
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## Array Creation Operator
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`[x1, ...]` – The `array(x1, ...) function.`
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## Tuple Creation Operator
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`(x1, x2, ...)` – The `tuple(x2, x2, ...) function.`
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## Associativity
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All binary operators have left associativity. For example, `1 + 2 + 3` is transformed to `plus(plus(1, 2), 3)`.
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Sometimes this doesn't work the way you expect. For example, ` SELECT 4 > 2 > 3` will result in 0.
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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.
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## Checking for `NULL`
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ClickHouse supports the `IS NULL` and `IS NOT NULL` operators.
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### IS NULL {#operator-is-null}
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- For [Nullable](../data_types/nullable.md) type values, the `IS NULL` operator returns:
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- `1`, if the value is `NULL`.
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- `0` otherwise.
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- For other values, the `IS NULL` operator always returns `0`.
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```bash
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:) SELECT x+100 FROM t_null WHERE y IS NULL
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SELECT x + 100
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FROM t_null
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WHERE isNull(y)
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┌─plus(x, 100)─┐
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│ 101 │
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└──────────────┘
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1 rows in set. Elapsed: 0.002 sec.
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```
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### IS NOT NULL
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- For [Nullable](../data_types/nullable.md) type values, the `IS NOT NULL` operator returns:
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- `0`, if the value is `NULL`.
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- `1` otherwise.
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- For other values, the `IS NOT NULL` operator always returns `1`.
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```bash
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:) SELECT * FROM t_null WHERE y IS NOT NULL
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SELECT *
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FROM t_null
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WHERE isNotNull(y)
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┌─x─┬─y─┐
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│ 2 │ 3 │
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└───┴───┘
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1 rows in set. Elapsed: 0.002 sec.
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```
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[Original article](https://clickhouse.yandex/docs/en/query_language/operators/) <!--hide-->
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