Postgresql 动态 SQL 查询执行

Question

我有一个使用一些 If Else 条件动态生成 SELECT 查询的函数。我将该查询存储在 TEXT 类型变量中作为

    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
    $BODY$
...................
................
...................
        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
...........................
.............................
.......................
    END;
    $BODY$
    LANGUAGE plpgsql VOLATILE

但是对于 plpgsql(PL/SQL for postgres)，我不知道如何在变量中执行相同的查询。请在这件事上给予我帮助 。提前致谢

Answer 1

来自文档(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.

换句话说:

将字符串中的 INTO old_ans_col_val 移动到您EXECUTE 的位置。