From 29d5ba52238be7832cbbd7a3c2dab10956e07da9 Mon Sep 17 00:00:00 2001 From: Alexey Milovidov Date: Mon, 25 Apr 2022 03:00:58 +0200 Subject: [PATCH] Resubmit two wrong doc changes --- docs/zh/sql-reference/data-types/map.md | 108 +++++++++++++++++- .../sql-reference/statements/alter/setting.md | 58 +++++++++- 2 files changed, 164 insertions(+), 2 deletions(-) mode change 120000 => 100644 docs/zh/sql-reference/data-types/map.md mode change 120000 => 100644 docs/zh/sql-reference/statements/alter/setting.md diff --git a/docs/zh/sql-reference/data-types/map.md b/docs/zh/sql-reference/data-types/map.md deleted file mode 120000 index 20de64e06d7..00000000000 --- a/docs/zh/sql-reference/data-types/map.md +++ /dev/null @@ -1 +0,0 @@ -../../../en/sql-reference/data-types/map.md \ No newline at end of file diff --git a/docs/zh/sql-reference/data-types/map.md b/docs/zh/sql-reference/data-types/map.md new file mode 100644 index 00000000000..4ef0bca74a6 --- /dev/null +++ b/docs/zh/sql-reference/data-types/map.md @@ -0,0 +1,107 @@ +--- +toc_priority: 65 +toc_title: Map(key, value) +--- + +# Map(key, value) {#data_type-map} + +`Map(key, value)` 可以存储 `key:value` 键值对类型的数据。 + +**参数** + +- `key` — 键值对的key，类型可以是：[String](../../sql-reference/data-types/string.md), [Integer](../../sql-reference/data-types/int-uint.md), [LowCardinality](../../sql-reference/data-types/lowcardinality.md), 或者 [FixedString](../../sql-reference/data-types/fixedstring.md). +- `value` — 键值对的value，类型可以是：[String](../../sql-reference/data-types/string.md), [Integer](../../sql-reference/data-types/int-uint.md), [Array](../../sql-reference/data-types/array.md), [LowCardinality](../../sql-reference/data-types/lowcardinality.md), 或者 [FixedString](../../sql-reference/data-types/fixedstring.md). + +使用 `a['key']` 可以从 `a Map('key', 'value')` 类型的列中获取到对应的值，这是一个线性复杂度的查询。 + +**示例** + +示例表: + +``` sql +CREATE TABLE table_map (a Map(String, UInt64)) ENGINE=Memory; +INSERT INTO table_map VALUES ({'key1':1, 'key2':10}), ({'key1':2,'key2':20}), ({'key1':3,'key2':30}); +``` + +查询 `key2` 的所有值: + +```sql +SELECT a['key2'] FROM table_map; +``` +查询结果: + +```text +┌─arrayElement(a, 'key2')─┐ +│ 10 │ +│ 20 │ +│ 30 │ +└─────────────────────────┘ +``` + +如果在 `Map()` 类型的列中，查询的 `key` 值不存在，那么根据 `value` 的类型，查询结果将会是数字0，空字符串或者空数组。 + +```sql +INSERT INTO table_map VALUES ({'key3':100}), ({}); +SELECT a['key3'] FROM table_map; +``` + +查询结果: + +```text +┌─arrayElement(a, 'key3')─┐ +│ 100 │ +│ 0 │ +└─────────────────────────┘ +┌─arrayElement(a, 'key3')─┐ +│ 0 │ +│ 0 │ +│ 0 │ +└─────────────────────────┘ +``` + +## 将Tuple类型转换成Map类型 {#map-and-tuple} + +您可以使用 [CAST](../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-cast) 方法将 `Tuple()` 转换成 `Map()` ： + +``` sql +SELECT CAST(([1, 2, 3], ['Ready', 'Steady', 'Go']), 'Map(UInt8, String)') AS map; +``` + +``` text +┌─map───────────────────────────┐ +│ {1:'Ready',2:'Steady',3:'Go'} │ +└───────────────────────────────┘ +``` + +## Map.keys 和 Map.values 单独使用 {#map-subcolumns} + +为了更好使用 `Map` 类型，在一定的场景下，可以单独使用 `keys` 或者 `values`，而不需要将整个列的数据都读取出来。 + +**示例** + +查询: + +``` sql +CREATE TABLE t_map (`a` Map(String, UInt64)) ENGINE = Memory; +INSERT INTO t_map VALUES (map('key1', 1, 'key2', 2, 'key3', 3)); +SELECT a.keys FROM t_map; +SELECT a.values FROM t_map; +``` + +结果: + +``` text +┌─a.keys─────────────────┐ +│ ['key1','key2','key3'] │ +└────────────────────────┘ +┌─a.values─┐ +│ [1,2,3] │ +└──────────┘ +``` + +**另请参阅** + +- [map()](../../sql-reference/functions/tuple-map-functions.md#function-map) function +- [CAST()](../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-cast) function + +[Original article](https://clickhouse.com/docs/zh/sql-reference/data-types/map/) diff --git a/docs/zh/sql-reference/statements/alter/setting.md b/docs/zh/sql-reference/statements/alter/setting.md deleted file mode 120000 index 12fdba11505..00000000000 --- a/docs/zh/sql-reference/statements/alter/setting.md +++ /dev/null @@ -1 +0,0 @@ -../../../../en/sql-reference/statements/alter/setting.md \ No newline at end of file diff --git a/docs/zh/sql-reference/statements/alter/setting.md b/docs/zh/sql-reference/statements/alter/setting.md new file mode 100644 index 00000000000..83998a20237 --- /dev/null +++ b/docs/zh/sql-reference/statements/alter/setting.md @@ -0,0 +1,57 @@ +--- +toc_priority: 38 +toc_title: SETTING +--- + +# 表设置操作 {#table_settings_manipulations} + +这是一组更改表设置的操作。你可以修改设置或将其重置为默认值。单个查询可以同时更改多个设置。 如果指定名称的设置不存在，则查询会引发异常。 + +**语法** + +``` sql +ALTER TABLE [db].name [ON CLUSTER cluster] MODIFY|RESET SETTING ... +``` + +!!! note "注意" + 这些查询只能应用于 [MergeTree](../../../engines/table-engines/mergetree-family/mergetree.md) 表。 + + +## 修改设置 {#alter_modify_setting} + +更改表设置 + +**语法** + +```sql +MODIFY SETTING setting_name=value [, ...] +``` + +**示例** + +```sql +CREATE TABLE example_table (id UInt32, data String) ENGINE=MergeTree() ORDER BY id; +ALTER TABLE example_table MODIFY SETTING max_part_loading_threads=8, max_parts_in_total=50000; +``` + +## 重置设置 {#alter_reset_setting} + +重置表设置为默认值。如果设置处于默认状态，则不采取任何操作。 + +**语法** + +```sql +RESET SETTING setting_name [, ...] +``` + +**示例** + +```sql +CREATE TABLE example_table (id UInt32, data String) ENGINE=MergeTree() ORDER BY id + SETTINGS max_part_loading_threads=8; +ALTER TABLE example_table RESET SETTING max_part_loading_threads; +``` + +**参见** + +- [MergeTree settings](../../../operations/settings/merge-tree-settings.md)