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Merge pull request #66534 from Blargian/docs_joinGetOrNull
[Docs] add `joinGetOrNull`
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Sergei Trifonov
GitHub
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d5c412e86a
@ -2449,11 +2449,11 @@ As you can see, `runningAccumulate` merges states for each group of rows separat
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## joinGet
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The function lets you extract data from the table the same way as from a [dictionary](../../sql-reference/dictionaries/index.md).
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Gets the data from [Join](../../engines/table-engines/special/join.md#creating-a-table) tables using the specified join key.
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The function lets you extract data from the table the same way as from a [dictionary](../../sql-reference/dictionaries/index.md). Gets the data from [Join](../../engines/table-engines/special/join.md#creating-a-table) tables using the specified join key.
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:::note
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Only supports tables created with the `ENGINE = Join(ANY, LEFT, <join_keys>)` statement.
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:::
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**Syntax**
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@ -2463,26 +2463,32 @@ joinGet(join_storage_table_name, `value_column`, join_keys)
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**Arguments**
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- `join_storage_table_name` — an [identifier](../../sql-reference/syntax.md#syntax-identifiers) indicating where the search is performed. The identifier is searched in the default database (see setting `default_database` in the config file). To override the default database, use `USE db_name` or specify the database and the table through the separator `db_name.db_table` as in the example.
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- `join_storage_table_name` — an [identifier](../../sql-reference/syntax.md#syntax-identifiers) indicating where the search is performed.
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- `value_column` — name of the column of the table that contains required data.
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- `join_keys` — list of keys.
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:::note
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The identifier is searched for in the default database (see setting `default_database` in the config file). To override the default database, use `USE db_name` or specify the database and the table through the separator `db_name.db_table` as in the example.
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:::
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**Returned value**
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Returns a list of values corresponded to list of keys.
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If certain does not exist in source table then `0` or `null` will be returned based on [join_use_nulls](../../operations/settings/settings.md#join_use_nulls) setting.
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- Returns a list of values corresponded to the list of keys.
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:::note
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If a certain key does not exist in source table then `0` or `null` will be returned based on [join_use_nulls](../../operations/settings/settings.md#join_use_nulls) setting during table creation.
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More info about `join_use_nulls` in [Join operation](../../engines/table-engines/special/join.md).
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:::
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**Example**
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Input table:
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```sql
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CREATE DATABASE db_test
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CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id) SETTINGS join_use_nulls = 1
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INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13)
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CREATE DATABASE db_test;
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CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
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INSERT INTO db_test.id_val VALUES (1, 11)(2, 12)(4, 13);
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SELECT * FROM db_test.id_val;
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```
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```text
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@ -2496,18 +2502,116 @@ INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13)
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Query:
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```sql
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SELECT joinGet(db_test.id_val, 'val', toUInt32(number)) from numbers(4) SETTINGS join_use_nulls = 1
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SELECT number, joinGet(db_test.id_val, 'val', toUInt32(number)) from numbers(4);
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```
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Result:
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```text
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┌─joinGet(db_test.id_val, 'val', toUInt32(number))─┐
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│ 0 │
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│ 11 │
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│ 12 │
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│ 0 │
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└──────────────────────────────────────────────────┘
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┌─number─┬─joinGet('db_test.id_val', 'val', toUInt32(number))─┐
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1. │ 0 │ 0 │
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2. │ 1 │ 11 │
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3. │ 2 │ 12 │
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4. │ 3 │ 0 │
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└────────┴────────────────────────────────────────────────────┘
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```
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Setting `join_use_nulls` can be used during table creation to change the behaviour of what gets returned if no key exists in the source table.
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```sql
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CREATE DATABASE db_test;
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CREATE TABLE db_test.id_val_nulls(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id) SETTINGS join_use_nulls=1;
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INSERT INTO db_test.id_val_nulls VALUES (1, 11)(2, 12)(4, 13);
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SELECT * FROM db_test.id_val_nulls;
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```
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```text
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┌─id─┬─val─┐
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│ 4 │ 13 │
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│ 2 │ 12 │
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│ 1 │ 11 │
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└────┴─────┘
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```
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Query:
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```sql
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SELECT number, joinGet(db_test.id_val_nulls, 'val', toUInt32(number)) from numbers(4);
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```
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Result:
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```text
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┌─number─┬─joinGet('db_test.id_val_nulls', 'val', toUInt32(number))─┐
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1. │ 0 │ ᴺᵁᴸᴸ │
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2. │ 1 │ 11 │
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3. │ 2 │ 12 │
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4. │ 3 │ ᴺᵁᴸᴸ │
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└────────┴──────────────────────────────────────────────────────────┘
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```
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## joinGetOrNull
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Like [joinGet](#joinget) but returns `NULL` when the key is missing instead of returning the default value.
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**Syntax**
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```sql
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joinGetOrNull(join_storage_table_name, `value_column`, join_keys)
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```
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**Arguments**
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- `join_storage_table_name` — an [identifier](../../sql-reference/syntax.md#syntax-identifiers) indicating where the search is performed.
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- `value_column` — name of the column of the table that contains required data.
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- `join_keys` — list of keys.
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:::note
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The identifier is searched for in the default database (see setting `default_database` in the config file). To override the default database, use `USE db_name` or specify the database and the table through the separator `db_name.db_table` as in the example.
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:::
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**Returned value**
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- Returns a list of values corresponded to the list of keys.
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:::note
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If a certain key does not exist in source table then `NULL` is returned for that key.
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:::
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**Example**
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Input table:
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```sql
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CREATE DATABASE db_test;
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CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
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INSERT INTO db_test.id_val VALUES (1, 11)(2, 12)(4, 13);
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SELECT * FROM db_test.id_val;
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```
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```text
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┌─id─┬─val─┐
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│ 4 │ 13 │
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│ 2 │ 12 │
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│ 1 │ 11 │
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└────┴─────┘
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```
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Query:
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```sql
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SELECT number, joinGetOrNull(db_test.id_val, 'val', toUInt32(number)) from numbers(4);
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```
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Result:
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```text
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┌─number─┬─joinGetOrNull('db_test.id_val', 'val', toUInt32(number))─┐
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1. │ 0 │ ᴺᵁᴸᴸ │
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2. │ 1 │ 11 │
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3. │ 2 │ 12 │
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4. │ 3 │ ᴺᵁᴸᴸ │
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└────────┴──────────────────────────────────────────────────────────┘
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```
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## catboostEvaluate
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@ -1866,6 +1866,7 @@ jdbc
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jemalloc
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jeprof
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joinGet
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joinGetOrNull
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json
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jsonMergePatch
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jsonasstring
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