# Parameters

***prestd*** uses query string to apply filtering, sorting, paginating, and etc to api queries.

### Filters

HTTP method `GET`

| query string                             | Description                                                                                                                                                                                |
| ---------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `_page={set page number}`                | the api return is paged, this parameter sets which page you want                                                                                                                           |
| `_page_size={number to return by pages}` | delimits the number of records per page, default `10`. Every time you specify a page size, you must include the page you are accessing.                                                    |
| `?_select={field name 1},{fiel name 2}`  | Limit fields list on result - sql ansii standard                                                                                                                                           |
| `?_count={field name}`                   | Count per field - `*` representation all fields                                                                                                                                            |
| `?_count_first=true`                     | Query string `_count` returns a list, passing this parameter will return the first record as a non-list object, **by default** this parameter is set to `false` (*return list non-object*) |
| `?_renderer=xml`                         | Set API render syntax, supported: `json` (by default), `xml`                                                                                                                               |
| `?_distinct=true`                        | `DISTINCT` clause with SELECT                                                                                                                                                              |
| `?_order={FIELD}`                        | `ORDER BY` in sql query. For `DESC` order, use the prefix `-`. For *multiple* orders, the fields are separated by comma `fieldname01,-fieldname02,fieldname03`                             |
| `?_groupby={FIELD}`                      | `GROUP BY` in sql query, The grouper is more complicated, a topic has been created to describe how to use                                                                                  |
| `?{FIELD NAME}={VALUE}`                  | Filter by field, you can set as many query parameters as needed                                                                                                                            |

#### Functions support

Used to perform data **aggregation**(**grouping** and **selection**)

| name     | Use in request   |
| -------- | ---------------- |
| SUM      | `sum:field`      |
| AVG      | `avg:field`      |
| MAX      | `max:field`      |
| MIN      | `min:field`      |
| STDDEV   | `stddev:field`   |
| VARIANCE | `variance:field` |

**`SELECT` with function:**

```
/{DATABASE}/{SCHEMA}/{TABLE}?_select=fieldname00,sum:fieldname01&_groupby=fieldname01
```

**`GROUP BY` with function:**

```
/{DATABASE}/{SCHEMA}/{TABLE}?_groupby=fieldname->>having:GROUPFUNC:FIELDNAME:CONDITION:VALUE-CONDITION
/{DATABASE}/{SCHEMA}/{TABLE}?_select=fieldname00,sum:fieldname01&_groupby=fieldname01->>having:sum:fieldname01:$gt:500
```

### Operators Reference Guide

The following operators are used for filtering data in queries. Each operator defines a specific matching condition that determines which records are included in the result set.

***

| Operator         | Description                                                  | Example Usage                                   |
| ---------------- | ------------------------------------------------------------ | ----------------------------------------------- |
| `$eq`            | Matches values that are equal to a specified value.          | `status=$eq.active`                             |
| `$gt`            | Matches values greater than a specified value.               | `age=$gt.25`                                    |
| `$gte`           | Matches values greater than or equal to a specified value.   | `salary=$gte.50000`                             |
| `$lt`            | Matches values less than a specified value.                  | `experience=$lt.5`                              |
| `$lte`           | Matches values less than or equal to a specified value.      | `rating=$lte.4.5`                               |
| `$ne`            | Matches values that are not equal to a specified value.      | `status=$ne.closed`                             |
| `$in`            | Matches any of the values specified in an array.             | `role=$in.admin,editor,viewer`                  |
| `$nin`           | Matches none of the values specified in an array.            | `department=$nin.hr,finance`                    |
| `$null`          | Matches if the field value is null.                          | `remarks=$null`                                 |
| `$notnull`       | Matches if the field value is not null.                      | `remarks=$notnull`                              |
| `$true`          | Matches if the field value is true.                          | `is_verified=$true`                             |
| `$nottrue`       | Matches if the field value is not true.                      | `is_verified=$nottrue`                          |
| `$false`         | Matches if the field value is false.                         | `is_active=$false`                              |
| `$notfalse`      | Matches if the field value is not false.                     | `is_active=$notfalse`                           |
| `$like`          | Matches the entire string (case-sensitive).                  | `name=$like.John%`                              |
| `$ilike`         | Matches the entire string, case-insensitive.                 | `city=$ilike.mumbai%`                           |
| `$nlike`         | Excludes matches that cover the entire string.               | `email=$nlike.%@test.com`                       |
| `$nilike`        | Excludes matches, case-insensitive.                          | `email=$nilike.%@gmail.com`                     |
| `$ltreelanc`     | Checks if left argument is an ancestor of right (or equal).  | `category_path=$ltreelanc.electronics`          |
| `$ltreerdesc`    | Checks if left argument is a descendant of right (or equal). | `category_path=$ltreerdesc.electronics.mobiles` |
| `$ltreematch`    | Checks if ltree matches lquery.                              | `tags=$ltreematch.tech.*`                       |
| `$ltreematchtxt` | Checks if ltree matches ltxtquery.                           | `tags=$ltreematchtxt.smartphone & android`      |

***

### Notes

* Comma (`,`) is used to separate multiple values in `$in` and `$nin` operators.
* Pattern matching operators like `$like` and `$ilike` support SQL wildcards (`%`, `_`).
* LTree operators (`$ltreelanc`, `$ltreerdesc`, etc.) are useful for hierarchical data filtering.


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.prestd.com/api-reference/parameters.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.