Using DBMS_SQL for Dynamic SQL Execution in EDB Postgres Advanced Server 16

A common use case for using DBMS_SQL subprograms in EDB Postgres Advanced Server 16 is dynamic SQL execution in stored procedures. This is particularly useful when the SQL statement to be executed is not known at compile time and must be constructed at runtime.

Using DBMS_SQL subprograms in EDB Postgres Advanced Server 16 allows for dynamic SQL execution. Here's a practical example:

Suppose you want to create a function that dynamically selects data from a given table and column names provided at runtime.

1. Function Definition:
   

   CREATE OR REPLACE FUNCTION dynamic_query(table_name text, column_name text)
   RETURNS SETOF record AS $$
   DECLARE
       cur_id INTEGER;
       query TEXT;
       result_set RECORD;
   BEGIN
       cur_id := DBMS_SQL.OPEN_CURSOR();
       query := 'SELECT ' || quote_ident(column_name) || ' FROM ' || quote_ident(table_name);
       DBMS_SQL.PARSE(cur_id, query);
       DBMS_SQL.DEFINE_COLUMN(cur_id, 1, result_set);
       DBMS_SQL.EXECUTE(cur_id);
   
       LOOP
           EXIT WHEN NOT DBMS_SQL.FETCH_ROWS(cur_id) > 0;
           DBMS_SQL.COLUMN_VALUE(cur_id, 1, result_set);
           RETURN NEXT result_set;
       END LOOP;
   
       DBMS_SQL.CLOSE_CURSOR(cur_id);
   END;
   $$ LANGUAGE plpgsql;
   
   

2. Function Usage:
   

   -- Assuming you have a table 'employees' with a column 'name'
   SELECT * FROM dynamic_query('employees', 'name');
   
   

In this example, the dynamic_query function takes a table name and column name as input, constructs a SELECT query, executes it, and returns the result set. This approach is useful when you need to build and execute SQL queries dynamically based on runtime conditions.

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