Postgresql动态SQL查询执行

Question

我有一个函数,它使用一些If Else条件动态生成SELECT查询.我已将该查询存储在TEXT类型变量中

    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

但是使用plpgsql(用于postgres的PL/SQL)我不知道如何在变量中执行相同的查询.请帮我解决一下这个 .提前致谢

Answer 1

来自文档（Postgres 9.1）：

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

其中 command-string 是一个表达式，生成包含要执行的命令的字符串（文本类型）。可选目标是记录变量、行变量或逗号分隔的简单变量和记录/行字段列表，命令的结果将存储在其中。

换句话说：

将字符串中的移动INTO old_ans_col_val到您所在的位置EXECUTE。