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nullif and reformat utility.md
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Alex-Monahan authored Jun 26, 2023
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Expand Up @@ -8,28 +8,29 @@ expanded: Functions
## Utility Functions
The functions below are difficult to categorize into specific function types and are broadly useful.

| Function | Description | Example | Result |
| Function| Description| Example| Result|
|:----------------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:---------------------------------------|:--------------------------------------|
| `alias(column)` | Return the name of the column | `alias(column1)` | `'column1'` |
| `checkpoint(database)` | Synchronize WAL with file for (optional) database without interrupting transactions. | `checkpoint(my_db)` | success boolean |
| `coalesce(expr, ...)` | Return the first expression that evaluates to a non-`NULL` value. Accepts 1 or more parameters. Each expression can be a column, literal value, function result, or many others. | `coalesce(NULL,NULL,'default_string')` | `'default_string'` |
| `ifnull(expr, other)` | A two-argument version of coalesce | `ifnull(NULL,'default_string')` | `'default_string'` |
| `current_schema()` | Return the name of the currently active schema. Default is main. | `current_schema()` | `'main'` |
| `current_schemas(boolean)` | Return list of schemas. Pass a parameter of `True` to include implicit schemas. | `current_schemas(true)` | `['temp', 'main', 'pg_catalog']` |
| `current_setting('setting_name')` | Return the current value of the configuration setting | `current_setting('access_mode')` | `'automatic'` |
| `currval('sequence_name')` | Return the current value of the sequence. Note that `nextval` must be called at least once prior to calling `currval`. | `currval('my_sequence_name')` | `1` |
| `force_checkpoint(database)` | Synchronize WAL with file for (optional) database interrupting transactions. | `force_checkpoint(my_db)` | success boolean |
| `gen_random_uuid()` | Alias of `uuid`. Return a random uuid similar to this: eeccb8c5-9943-b2bb-bb5e-222f4e14b687. | `gen_random_uuid()` | various |
| `hash(`*`value`*`)` | Returns an integer with the hash of the *value* | `hash('🦆')` | `2595805878642663834` |
| `icu_sort_key(string , collator)` | Surrogate key used to sort special characters according to the specific locale. Collator parameter is optional. Valid only when ICU extension is installed. | `icu_sort_key('ö','DE')` | 460145960106 |
| `md5(string)` | Return an md5 one-way hash of the *string*. | `md5('123')` | `'202cb962ac59075b964b07152d234b70'` |
| `nextval('sequence_name')` | Return the following value of the sequence. | `nextval('my_sequence_name')` | `2` |
| `pg_typeof(expression)` | Returns the lower case name of the data type of the result of the expression. For Postgres compatibility. | `pg_typeof('abc')` | `'varchar'` |
| `stats(expression)` | Returns a string with statistics about the expression. Expression can be a column, constant, or SQL expression. | `stats(5)` | `'[Min: 5, Max: 5][Has Null: false]'` |
| `txid_current()` | Returns the current transaction's ID (a `BIGINT`). It will assign a new one if the current transaction does not have one already. | `txid_current()` | various |
| `typeof(expression)` | Returns the name of the data type of the result of the expression. | `typeof('abc')` | `'VARCHAR'` |
| `uuid()` | Return a random uuid similar to this: eeccb8c5-9943-b2bb-bb5e-222f4e14b687. | `uuid()` | various |
| `version()` | Return the currently active version of DuckDB in this format: `v0.3.2` | `version()` | various |
| `alias(`*`column`*`)` | Return the name of the column| `alias(column1)` | `'column1'` |
| `checkpoint(`*`database`*`)`| Synchronize WAL with file for (optional) database without interrupting transactions. | `checkpoint(my_db)`| success boolean |
| `coalesce(`*`expr`*`, `*`...`*`)` | Return the first expression that evaluates to a non-`NULL` value. Accepts 1 or more parameters. Each expression can be a column, literal value, function result, or many others. | `coalesce(NULL,NULL,'default_string')` | `'default_string'`|
| `ifnull(`*`expr`*`, `*`other`*`)` | A two-argument version of coalesce | `ifnull(NULL,'default_string')` | `'default_string'`|
| `nullif(`*`a`*`, `*`b`*`)` | Return null if a = b, else return a. Equivalent to `CASE WHEN a=b THEN NULL ELSE a END`. | `nullif(1+1, 2)` | `NULL`|
| `current_schema()`| Return the name of the currently active schema. Default is main. | `current_schema()` | `'main'`|
| `current_schemas(`*`boolean`*`)`| Return list of schemas. Pass a parameter of `True` to include implicit schemas.| `current_schemas(true)`| `['temp', 'main', 'pg_catalog']`|
| `current_setting(`*`'setting_name'`*`)` | Return the current value of the configuration setting| `current_setting('access_mode')` | `'automatic'` |
| `currval(`*`'sequence_name'`*`)`| Return the current value of the sequence. Note that `nextval` must be called at least once prior to calling `currval`. | `currval('my_sequence_name')`| `1` |
| `force_checkpoint(`*`database`*`)`| Synchronize WAL with file for (optional) database interrupting transactions. | `force_checkpoint(my_db)`| success boolean |
| `gen_random_uuid()` | Alias of `uuid`. Return a random uuid similar to this: eeccb8c5-9943-b2bb-bb5e-222f4e14b687. | `gen_random_uuid()`| various |
| `hash(`*`value`*`)` | Returns an integer with the hash of the *value*| `hash('🦆')` | `2595805878642663834` |
| `icu_sort_key(`*`string`*`, `*`collator`*`)` | Surrogate key used to sort special characters according to the specific locale. Collator parameter is optional. Valid only when ICU extension is installed.| `icu_sort_key('ö','DE')` | 460145960106|
| `md5(`*`string`*`)` | Return an md5 one-way hash of the *string*.| `md5('123')` | `'202cb962ac59075b964b07152d234b70'`|
| `nextval(`*`'sequence_name'`*`)`| Return the following value of the sequence.| `nextval('my_sequence_name')`| `2` |
| `pg_typeof(`*`expression`*`)` | Returns the lower case name of the data type of the result of the expression. For Postgres compatibility.| `pg_typeof('abc')` | `'varchar'` |
| `stats(`*`expression`*`)` | Returns a string with statistics about the expression. Expression can be a column, constant, or SQL expression.| `stats(5)` | `'[Min: 5, Max: 5][Has Null: false]'` |
| `txid_current()`| Returns the current transaction's ID (a `BIGINT`). It will assign a new one if the current transaction does not have one already.| `txid_current()` | various |
| `typeof(`*`expression`*`)`| Returns the name of the data type of the result of the expression. | `typeof('abc')`| `'VARCHAR'` |
| `uuid()`| Return a random uuid similar to this: eeccb8c5-9943-b2bb-bb5e-222f4e14b687.| `uuid()` | various |
| `version()` | Return the currently active version of DuckDB in this format: `v0.3.2` | `version()`| various |

## Utility Table Functions
A table function is used in place of a table in a `FROM` clause.
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