MS SQL Server: Filter Query Results / Search Queries

Introduction

Hasura provides a powerful yet simple syntax to filter query results on MS SQL Server. This is useful for building search queries or filtering data based on some criteria. You can utilize arguments and operators to filter results based on equality, comparison, pattern matching, etc.

The where argument

You can use the where argument in your queries to filter results based on some field's values (even nested objects' fields). You can even use multiple filters in the same where clause using the _and or the _or operators.

For example, to fetch data for an author whose name is "Sidney":

query {
  authors(where: { name: { _eq: "Sidney" } }) {
    id
    name
  }
}

You can also use nested objects' fields to filter rows from a table and also filter the nested objects as well.

For example, to fetch a list of authors who have articles with a rating greater than 4 along with those articles:

query {
  authors(where: { articles: { rating: { _gt: 4 } } }) {
    id
    name
    articles(where: { rating: { _gt: 4 } }) {
      id
      title
      rating
    }
  }
}

Here _eq and _gt are examples of comparison operators that can be used in the where argument to filter on equality.

You can see the complete specification of the where argument in the API reference.

Filter nested objects

The where argument can be used in array relationships as well to filter the nested objects. Object relationships have only one nested object and hence they do not expose the where argument.

Example:

Fetch all authors with only their 5 rated articles:

GraphiQL

Query Variables

Request Headers

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Supported operators

Operator	Use case
Simple Comparison Operators	Utilize comparison operators to selectively filter results by evaluating a field against a specific value.
Boolean Operators	Employ boolean operators to refine result filters based on logical expressions.
Text Search Operators	Apply text search operators to narrow down results according to the presence of text in a field.
Geospatial Operators	Leverage geospatial operators to narrow results based on geographical location data.
Nested Objects	Navigate and filter results using nested object structures for advanced filtering.

The TRUE expression ( { } )

The expression {} evaluates to true if an object exists (even if it's null).

For example:

• any query with the condition { where: {} } will return all objects without applying any filter.
• any query with the condition { where: { nested_object: {} } } will return all objects for which atleast one nested_object exists.

Evaluation of null values in comparison expressions

If in any comparison expression a null value is passed, a type mismatch error will be thrown.

For example, the expression { where: {id: { _eq: null }}} will throw an error.