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.

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

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 or DateTime type is supported.

Examples:

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.

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

INSERT INTO test.Orders VALUES (1, 'Jarlsberg Cheese', toDateTime('2008-10-11 13:23:44'));

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.

Logical Negation Operator

NOT a The not(a) function.

Logical AND Operator

a AND b – Theand(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() function, each row will be replicated regardless of the "a" condition.

Conditional Expression

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

• For Nullable 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.

:) 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 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.

:) 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