来自具有多连接的其他表的informix更新

Question

以下查询似乎无效并且语法错误：

update const_acad_record
set const_acad_record.education_level = school_category_type.education_level
FROM school_category_type, sch_rec sch_rec
where const_acad_record.organization_ID = sch_rec.id and
sch_rec.ctgry = school_category_type.code

如果我将此转换为子查询，如下所示，它可以工作，但会更新比所需更多的记录：

update const_acad_record
set education_level = (SELECT education_level
FROM school_category_type sct, sch_rec sr
where const_acad_record.organization_ID = sr.id and
sr.ctgry = sct.code)

（education_level列来自表格school_category_type。）

Answer 1

您通常还需要一个语句级IsKeyboardFocusWithin子句，以将更新的记录数限制为具有匹配条目的记录。我认为在这个例子中，它可以采取以下形式：

WHERE

^{未经测试的SQL}

这会将行更新限制为具有匹配记录的行。如果没有语句级WHERE子句，则表（UPDATE const_acad_record SET education_level = (SELECT education_level FROM school_category_type sct JOIN sch_rec sr ON sr.ctgry = sct.code WHERE const_acad_record.organization_ID = sr.id) WHERE EXISTS(SELECT education_level FROM school_category_type sct JOIN sch_rec sr ON sr.ctgry = sct.code WHERE const_acad_record.organization_ID = sr.id) ）中的所有行都会更新，而const_acad_record中没有匹配条目的行将设置为SELECT。

如果我更好地理解表格，我可能会在语句级查询中使用IN子句，例如：

NULL

^{未经测试的SQL}

在其他问题中，不清楚列UPDATE const_acad_record SET Education_Level = (SELECT education_level FROM school_category_type sct JOIN sch_rec sr ON sr.ctgry = sct.code WHERE const_acad_record.organization_ID = sr.id) WHERE Organization_ID IN (SELECT sr.id FROM school_category_type sct JOIN sch_rec sr ON sr.ctgry = sct.code) 是来自表education_level还是表school_category_type;这可能会改变适当的。