sql - 从 plpgsql 标识符中的连接字符串中删除双引号

Question

我编写了以下函数，它从另一个表“parameters_ltree_{time_created}”返回记录，其中 time_created 是 historical_ltree 表中的一列。

CREATE OF REPLAE function get_my_path(date_string text, path_arg ltree) RETURNS SETOF  ltree AS
$BODY$
DECLARE
    p text;
    d text;
BEGIN
    d := quote_ident(date_string);
    p := 'parameters_ltree_';
    RETURN QUERY EXECUTE format(
    'SELECT  path from %I' || '%I
    WHERE path = %I
    ORDER BY path
    LIMIT 1'
    , p, date_string, path_arg);

END
$BODY$
LANGUAGE plpgsql;

SELECT id, path, get_my_path(to_char(time_created, 'YYYYMMDD')), path) from historical_ltree

该函数可以编译，但是当我在底部运行 SELECT 查询时，它会抛出一个语法错误:

ERROR: relation "parameters_ltree_" does not exist
LINE 1: SELECT path FROM parameters_ltree_"20161201"
                         ^

我尝试了很多不同的方法来使连接正常工作，但都无济于事，包括将 date_string 作为数字传递。

Answer 1

尝试更改为:

    RETURN QUERY EXECUTE format(
    'SELECT  path from %I
    WHERE path = %L
    ORDER BY path
    LIMIT 1'
    , 'parameters_ltree_'||date_string, path_arg);

https://www.postgresql.org/docs/current/static/functions-string.html

s formats the argument value as a simple string. A null value is treated as an empty string.

I treats the argument value as an SQL identifier, double-quoting it if necessary. It is an error for the value to be null (equivalent to quote_ident).

L quotes the argument value as an SQL literal. A null value is displayed as the string NULL, without quotes (equivalent to quote_nullable).