From 4784a945c1047c64a6bbabc830bf2114de094dc7 Mon Sep 17 00:00:00 2001 From: Ivan Blinkov Date: Thu, 6 Sep 2018 21:13:20 +0300 Subject: [PATCH] restore NULL literal section in query_language/syntax.md --- docs/en/query_language/syntax.md | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/docs/en/query_language/syntax.md b/docs/en/query_language/syntax.md index 5d7409ec502..11ffb2e6a91 100644 --- a/docs/en/query_language/syntax.md +++ b/docs/en/query_language/syntax.md @@ -70,6 +70,20 @@ For more information, see the section "Operators2". An array must consist of at least one item, and a tuple must have at least two items. Tuples have a special purpose for use in the IN clause of a SELECT query. Tuples can be obtained as the result of a query, but they can't be saved to a database (with the exception of Memory-type tables). + + +### NULL Literal + +Indicates that the value is missing. + +In order to store `NULL` in a table field, it must be of the [Nullable](../data_types/nullable.md#data_type-nullable) type. + +Depending on the data format (input or output), `NULL` may have a different representation. For more information, see the documentation for [data formats](../interfaces/formats.md#formats). + +There are many nuances to processing `NULL`. For example, if at least one of the arguments of a comparison operation is `NULL`, the result of this operation will also be `NULL`. The same is true for multiplication, addition, and other operations. For more information, read the documentation for each operation. + +In queries, you can check `NULL` using the [IS NULL](operators.md#operator-is-null) and [IS NOT NULL](operators.md#operator-is-not-null) operators and the related functions `isNull` and `isNotNull`. + ## Functions Functions are written like an identifier with a list of arguments (possibly empty) in brackets. In contrast to standard SQL, the brackets are required, even for an empty arguments list. Example: `now()`.