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Anna 2020-12-27 14:47:15 +03:00
parent 51b76f7367
commit 45b8ddd7ab
2 changed files with 13 additions and 13 deletions
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6
docs/en/operations/settings/settings.md
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@ -2472,12 +2472,12 @@ Default value: `0`.
## data_type_default_nullable {#data_type_default_nullable}
Allows data types without explicit modifiers in table definition will be [Nullable](../../sql-reference/data-types/nullable.md#data_type-nullable).
Allows data types without explicit modifiers in column definition will be [Nullable](../../sql-reference/data-types/nullable.md#data_type-nullable).
Possible values:
- 1 — `Nullable`-type expressions are allowed in a table definition.
- 0 — `Nullable`-type expressions are not allowed in a table definition.
- 1 — The data type in a column definition is `Nullable`.
- 0 — The data type in a column definition is not `Nullable`.
Default value: `0`.

20
docs/en/sql-reference/statements/create/table.md
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@ -16,8 +16,8 @@ By default, tables are created only on the current server. Distributed DDL queri
``` sql
CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
(
name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1] [compression_codec] [TTL expr1],
name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2] [compression_codec] [TTL expr2],
name1 [type1] [NULL|NOT NULL] [DEFAULT|MATERIALIZED|ALIAS expr1] [compression_codec] [TTL expr1],
name2 [type2] [NULL|NOT NULL] [DEFAULT|MATERIALIZED|ALIAS expr2] [compression_codec] [TTL expr2],
...
) ENGINE = engine
```
@ -57,6 +57,14 @@ In all cases, if `IF NOT EXISTS` is specified, the query won’t return an error
There can be other clauses after the `ENGINE` clause in the query. See detailed documentation on how to create tables in the descriptions of [table engines](../../../engines/table-engines/index.md#table_engines).
## NULL Or NOT NULL Modifiers {#null-modifiers}
`NULL` and `NOT NULL` modifiers after data type in column definition allow or do not allow it to be [Nullable](../../../sql-reference/data-types/nullable.md#data_type-nullable).
If the type is not `Nullable` and if `NULL` is specified, it will be treated as `Nullable`; if `NOT NULL` is specified, then no. For example, `INT NULL` is the same as `Nullable(INT)`. If the type is `Nullable` and `NULL` or `NOT NULL` modifiers are specified, the exception will be thrown.
See also [data_type_default_nullable](../../../operations/settings/settings.md#data_type_default_nullable) setting.
## Default Values {#create-default-values}
The column description can specify an expression for a default value, in one of the following ways: `DEFAULT expr`, `MATERIALIZED expr`, `ALIAS expr`.
@ -99,14 +107,6 @@ If you add a new column to a table but later change its default expression, the
It is not possible to set default values for elements in nested data structures.
## NULL Or NOT NULL Modifiers
`NULL` and `NOT NULL` modifiers after data type in table definition allow or do not allow it to be [Nullable](../../sql-reference/data-types/nullable.md#data_type-nullable).
If the type is not `Nullable` and if `NULL` is specified, it will be treated as `Nullable`; if `NOT NULL` is specified, then no. For example, `INT NULL` is the same as `Nullable(INT)`. If the type is `Nullable` and `NULL` or `NOT NULL` modifiers are specified, the exception will be thrown.
See also [data_type_default_nullable](../../operations/settings/settings.md#data_type_default_nullable) setting.
## Primary Key {#primary-key}
You can define a [primary key](../../../engines/table-engines/mergetree-family/mergetree.md#primary-keys-and-indexes-in-queries) when creating a table. Primary key can be specified in two ways: