Postgresql Dynamic SQL Query Execution

Question

I have a function which generates a SELECT query dynamically using some If Else conditions .I have stored that query in a TEXT type variable as

    CREATE OR REPLACE FUNCTION func_updateanswercodes(ans_id_param BIGINT, 
                              que_id_param BIGINT, 
                              overwrite_param INTEGER, 
                              new_ans_code_param CHARACTER VARYING)
    RETURNS INTEGER AS
    $BODY$
...................
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        dyn_sql = 'SELECT ' || que_col_name || ' INTO old_ans_col_val FROM';
                    IF SUBSTR(que_col_name, 0, 8) = 'pro_ans' THEN
                        dyn_sql = dyn_sql || ' profile_answers JOIN registrations ON (pro_ans_frn_pro_id = reg_frn_pro_id)';
                        ELSIF SUBSTR(que_col_name, 0, 8) = 'reg_ans' THEN
                        dyn_sql = dyn_sql || ' reg_answers ';
                        ELSIF SUBSTR(que_col_name, 0, 8) = 'tvl_ans' THEN
                        dyn_sql = dyn_sql || ' tvl_answers '; --35
                                END IF;
                    dyn_sql = dyn_sql || ' WHERE';
                    IF SUBSTR(que_col_name, 0, 8) = 'pro_ans' THEN
                        dyn_sql = dyn_sql || ' reg_id ';
                        ELSIF SUBSTR(que_col_name, 0, 8) = 'reg_ans' THEN
                        dyn_sql = dyn_sql || ' reg_ans_frn_reg_id ';
                        ELSIF SUBSTR(que_col_name, 0, 8) = 'tvl_ans' THEN
                        dyn_sql = dyn_sql || ' tvl_ans_frn_reg_id ';
                                END IF;
                        dyn_sql = dyn_sql || '= ' || CAST(temp_reg AS VARCHAR) ||';'

    /* Here want to execute that query in variable dync_sql
...........................
.............................
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    END;
    $BODY$
    LANGUAGE plpgsql VOLATILE

But with plpgsql(PL/SQL for postgres) I don't know how to execute this same query in a variable . Please help me with this . Thanks in Advance

Answer 1

From the docs (Postgres 9.1):

EXECUTE command-string [ INTO [STRICT] target ] [ USING expression [, ... ] ];

where command-string is an expression yielding a string (of type text) containing the command to be executed. The optional target is a record variable, a row variable, or a comma-separated list of simple variables and record/row fields, into which the results of the command will be stored.

In other words:

Move the INTO old_ans_col_val from the String to the place where you EXECUTE it.

Answer 2

Use EXECUTE for details see the manual

Note that you have to take your INTO part out of the query string and put it at the end.

EXECUTE dyn_sql INTO old_ans_col_val;