function - 使用执行 (plpgsql) 创建函数

Question

我想创建一个函数，根据表名返回主键的下一个值：

CREATE OR REPLACE FUNCTION next_pk (_table varchar) RETURNS INTEGER AS $$
    BEGIN
        RETURN EXECUTE 'SELECT COALESCE (MAX (primary_key), 0) + 1 FROM ' || quote_ident (_table) || ' limit 1';
    END;
$$ LANGUAGE plpgsql;

select next_pk ('myTable');

但它给出了以下错误：

ERROR:  type "execute" does not exist
LINE 1: SELECT EXECUTE 'SELECT COALESCE (MAX (primary_key), 0) + 1 F...

有什么线索吗？谢谢。

Answer 1

您需要整数变量并“执行”：

CREATE OR REPLACE FUNCTION next_pk (_table varchar) RETURNS INTEGER AS $$
DECLARE
    result integer;    
BEGIN  
    EXECUTE 
        'SELECT COALESCE (MAX (primary_key), 0) + 1 FROM ' || quote_ident (_table) 
        INTO result;
    RETURN result;
END;
$$ LANGUAGE plpgsql;

select next_pk ('myTable');