added Postgresql positional-parameters

content/postgresql/concepts/positional-parameters/positional-parameters.md

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+Title: 'Postional parameters in sql'
+Description: 'positional parameters are placeholders used in SQL statements for passing values dynamically to queries or functions. '
+Subjects:
+  - 'Web Development'
+  - 'Computer Science'
+  - 'postgresql'
+  Tags:
+  - 'positional-parameters'
+  - 'Documentation'
+  CatalogContent:
+  - 'getting-started-off-platform-for-data-science'
+  - 'paths/design-databases-with-postgresql'
+  - 'paths/computer-science'
+
+## Syntax
+
+**Positional parameters** are often utilized in prepared statements or in dynamic SQL queries.They must always appear first in a parameter set. In access method services, positional parameters are never optional.They serve as placeholders for dynamic values that will be supplied later when executing the query or prepared statement.
+When a query or prepared statement is executed, the positional parameters are replaced with actual values based on the order in which they appear and the values provided during execution.
+
+## Example
+Here's an example of positional parameters in PostgreSQL:
+
+Suppose we have a table called employees with columns id, name, and age. We want to retrieve employees whose age is greater than a specified value, and we want to make this value dynamic using positional parameters.
+
+First, let's create a simple table:
+```sql
+CREATE TABLE employees (
+    id SERIAL PRIMARY KEY,
+    name TEXT,
+    age INTEGER
+);
+
+INSERT INTO employees (name, age) VALUES
+('John', 30),
+('Alice', 25),
+('Bob', 35);
+
+```
+Now, let's write a query using positional parameters to retrieve employees older than a specified age:
+```sql
+PREPARE get_older_employees (INTEGER) AS
+SELECT * FROM employees WHERE age > $1;
+
+```
+In this query:
+
+PREPARE creates a prepared statement named get_older_employees.
+(INTEGER) specifies the data type of the positional parameter.
+$1 is the positional parameter reference.
+Now, we can execute the prepared statement with a specific value for the age parameter:
+
+```sql
+EXECUTE get_older_employees(25);
+
+```
+This will return all employees whose age is greater than 25.
+
+The benefit of using positional parameters is that you can reuse the prepared statement with different parameter values without needing to rewrite the entire query. It also helps prevent SQL injection attacks by separating the query logic from the input values.