The json_agg function is useful for creating JSON arrays from query results, which can be particularly handy when working with JSON data in PostgreSQL. Path expressions are written in the SQL/JSON path language and can also include arithmetic expressions and functions. If the expression matches the queried JSON data, the corresponding SQL/JSON item is returned. They follow the ordering rules for B-tree operations outlined at Section 8.14.4. JSON query functions and operators pass the provided path expression to the path engine for evaluation. The standard comparison operators shown in Table 9.1 are available for jsonb, but not for json. The GROUP BY clause groups the results by department. The field/element/path extraction operators that accept integer JSON array subscripts all support negative subscripting from the end of arrays.I've managed to write the function BUT it only returns the first row. We covered the basics of JSON data types and functions, and how to extract data from JSON fields. I currently have the query hard coded in a node.js implementation but would like to move it into the Db and simply call a function. In this article, we explored different aspects of handling JSON data in PostgreSQL. We selected the department and used json_agg(name) to aggregate the names of employees in the “HR” department into a JSON array. I have a query which by itself produces several rows of data and I use the rowtojson function to format that data for use in a rest api.The result of this query will be: | department | employees | |-|-| | HR | | You can use the json_agg function to aggregate the names of employees in the “HR” department into a JSON array: SELECT department, json_agg(name) AS employees FROM employees WHERE department = 'HR' GROUP BY department Here’s an example of how to use the json_agg function to aggregate values from a table:Ĭonsider a table named employees: CREATE TABLE employees ( id serial PRIMARY KEY, name text, department text ) Īnd it contains the following data: | id | name | department | |-|-|-| | 1 | Alice | HR | | 2 | Bob | IT | | 3 | Carol | HR | | 4 | David | IT | Where expression is the value or column you want to aggregate into the JSON array. Here is the basic syntax for the json_agg function: json_agg(expression) This function is particularly useful when you want to combine rows or values into a single JSON array in the result of a query. It takes one or more values and returns a JSON array that contains those values as elements. The json_agg function is used to aggregate values into a JSON array in PostgreSQL database.
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