diff --git a/docs/en/data_types/enum.md b/docs/en/data_types/enum.md index 754b6651f56..247ec070190 100644 --- a/docs/en/data_types/enum.md +++ b/docs/en/data_types/enum.md @@ -1,26 +1,29 @@ +# Enum -# Enum8, Enum16 +Enumerated type storing pairs of the `'string' = integer` format. -Includes the `Enum8` and `Enum16` types. `Enum` saves the finite set of pairs of `'string' = integer`. In ClickHouse, all operations with the `Enum` data type are performed as if value contains integers, although the user is working with string constants. This is more effective in terms of performance than working with the `String` data type. +ClickHouse supports: -- `Enum8` is described by pairs of `'String' = Int8`. -- `Enum16` is described by pairs of `'String' = Int16`. +- 8-bit `Enum`. It can contain up to 256 values with enumeration of `[-128, 127]`. +- 16-bit `Enum`. It can contain up to 65536 values with enumeration of `[-32768, 32767]`. + +ClickHouse automatically chooses a type for `Enum` at data insertion. Also, you can use `Enum8` or `Enum16` types to be sure in size of storage. ## Usage examples Here we create a table with an `Enum8('hello' = 1, 'world' = 2)` type column: -``` +```sql CREATE TABLE t_enum ( - x Enum8('hello' = 1, 'world' = 2) + x Enum('hello' = 1, 'world' = 2) ) ENGINE = TinyLog ``` -This column `x` can only store the values that are listed in the type definition: `'hello'` or `'world'`. If you try to save any other value, ClickHouse will generate an exception. +This column `x` can only store the values that are listed in the type definition: `'hello'` or `'world'`. If you try to save any other value, ClickHouse will generate an exception. ClickHouse automatically chooses the 8-bit size for enumeration of this `Enum`. -``` +```sql :) INSERT INTO t_enum VALUES ('hello'), ('world'), ('hello') INSERT INTO t_enum VALUES @@ -35,12 +38,12 @@ INSERT INTO t_enum VALUES Exception on client: -Code: 49. DB::Exception: Unknown element 'a' for type Enum8('hello' = 1, 'world' = 2) +Code: 49. DB::Exception: Unknown element 'a' for type Enum('hello' = 1, 'world' = 2) ``` When you query data from the table, ClickHouse outputs the string values from `Enum`. -``` +```sql SELECT * FROM t_enum ┌─x─────┐ @@ -52,7 +55,7 @@ SELECT * FROM t_enum If you need to see the numeric equivalents of the rows, you must cast the `Enum` value to integer type. -``` +```sql SELECT CAST(x, 'Int8') FROM t_enum ┌─CAST(x, 'Int8')─┐ @@ -64,12 +67,12 @@ SELECT CAST(x, 'Int8') FROM t_enum To create an Enum value in a query, you also need to use `CAST`. -``` -SELECT toTypeName(CAST('a', 'Enum8(\'a\' = 1, \'b\' = 2)')) +```sql +SELECT toTypeName(CAST('a', 'Enum(\'a\' = 1, \'b\' = 2)')) -┌─toTypeName(CAST('a', 'Enum8(\'a\' = 1, \'b\' = 2)'))─┐ -│ Enum8('a' = 1, 'b' = 2) │ -└──────────────────────────────────────────────────────┘ +┌─toTypeName(CAST('a', 'Enum(\'a\' = 1, \'b\' = 2)'))─┐ +│ Enum8('a' = 1, 'b' = 2) │ +└─────────────────────────────────────────────────────┘ ``` ## General rules and usage