MySQL5.7编写存储过程报错'as在此位置无效，期望;'问题求助

你遇到的as is not valid in this position expecting ';'报错的直接诱因是最外层SELECT查询存在语法错误：

• 你给整段返回结果的SELECT查询额外套了一层括号，还在括号末尾追加了as ca的别名定义。这种写法仅适用于该查询作为子查询嵌套在其他外层查询中的场景，直接在存储过程中作为返回结果的独立查询，不允许在整体外层括号后追加别名，删掉最外层的括号和末尾的as ca即可解决当前报错。

你的代码中还存在几处会导致后续运行异常的问题：

• 所有形如:startDateTime的占位符被单引号包裹后，会被MySQL识别为固定字符串，不会作为动态参数解析。如果是存储过程的入参，直接写参数名即可，不需要加单引号；如果是要构造动态SQL，需要配合PREPARE、EXECUTE语法执行。
• coalesce(':stageCode')写法不符合函数要求，coalesce函数至少需要传入2个参数，作用是返回第一个非空的参数，此处如果是要判断参数是否为空，直接写:stageCode is null即可。
• stage_code in (':stageCode')写法存在逻辑问题，参数被单引号包裹后，即使传入逗号分隔的多个枚举值，也会被识别为单个字符串，无法匹配多值场景。

DROP PROCEDURE IF EXISTS load_content;

DELIMITER $$
-- 若需要传入参数，可在括号内定义，示例：CREATE PROCEDURE load_content(IN p_startDateTime DATETIME, IN p_endDateTime DATETIME)
CREATE PROCEDURE load_content()
BEGIN
       SELECT DISTINCT
        ca.id AS id, cp.provider_id  AS cpId,
        ca.license_start_date AS startDateTime,
        ca.license_end_date   AS endDateTime,
        ca.content_group_id AS contentGroupId,
        ca.episode AS episode,
        ca.series_id AS seriesId,
        ca.is_episode AS isEpisode,
        aw.stage_code AS stageCode,
        tal.title  AS title,
        tal.synopsis  AS synopsis,
        ta.content_type AS contentType
        FROM (SELECT * FROM content_asset
        WHERE (:startDateTime is null OR license_start_date <= :startDateTime)
        AND (:endDateTime is null OR license_end_date >= :endDateTime)
        AND (:id is null OR id = :id)
        AND (:isEpisode is null OR is_episode = :isEpisode)) as ca 
        INNER JOIN title_asset ta ON ca.title_asset_id = ta.id
        INNER JOIN (select * from title_asset_localized
        WHERE (:title is null OR title like CONCAT('%', :title, '%'))
        AND language = :language) tal ON ta.id = tal.title_asset_id
        INNER JOIN (select * from content_provider
        WHERE (:cpId is null OR provider_id like CONCAT('%', :cpId, '%' ) )) cp
        ON cp.idx = ca.provider_id
        INNER JOIN (select * from asset_workflow
        WHERE asset_type = :contentManagementType
        AND (:stageCode is null OR stage_code in (:stageCode))) as aw ON aw.asset_id = ca.id;
END $$ 
DELIMITER ;

内容的提问来源于stack exchange，提问作者Clara