mysql - #1064.您的 SQL 语法有错误；检查与 MySQL 服务器版本相对应的手册，了解在第 1 行 'NULL' 附近使用的正确语法

Question

我有以下代码。我收到如下错误:

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'NULL' at line 1

MySQL 代码:

set session group_concat_max_len = 8192*50;
SET @sql = NULL;

SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'select id, "',
      c.column_name,
      '" as word from limesurvey.lime_survey_697389 '
    ) SEPARATOR ' UNION ALL '
  ) INTO @sql
FROM information_schema.columns c
where c.table_name = 'limesurvey.lime_survey_697389'
  and c.column_name like '697389%'
  order by c.ordinal_position;


SET @sql 
  = CONCAT('select id, word
           from
           (', @sql, ') x order by id');


PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

有人可以帮忙吗？我是 MySQL 新手。

Answer 1

您不能为@sql 定义NULL 值。相反，你可以尝试这样:

SET @sql = '';

<罢工>

编辑:

您需要在存储的程序或函数中执行上述代码。 MYSQL 文档说:

MySQL supports the IF, CASE, ITERATE, LEAVE LOOP, WHILE, and REPEAT constructs for flow control within stored programs.