Question

我需要选择 n 表中的所有行，其中 n ＆gt;以毫秒为单位访问数据集。单个查询会导致错误“定义的字段太多”。我的猜测是它超过了255场限制。

SELECT * FROM ((((((((((((((((Forms 
LEFT JOIN Layouts ON Layouts.Name = Forms.Name) 
LEFT JOIN Layout ON Layout.Name = Forms.Name) 
LEFT JOIN Form ON Form.Name = Forms.Name) 
LEFT JOIN Sections ON Sections.ID] = Form.ID) 
LEFT JOIN Checks ON Checks.ID = Form.ID) 
LEFT JOIN Dates ON Dates.ID = Form.ID) 
LEFT JOIN Combos ON Combos.ID = Form.ID) 
LEFT JOIN Labels ON Labels.ID = Form.ID) 
LEFT JOIN Flash ON Flash.ID = Form.ID) 
LEFT JOIN Links ON Links.ID = Form.ID) 
LEFT JOIN Groups ON Groups.ID = Form.ID) 
LEFT JOIN Lists ON Lists.ID = Form.ID) 
LEFT JOIN Pictures ON Pictures.ID = Form.ID) 
LEFT JOIN Grids ON Grids.ID = Form.ID) 
LEFT JOIN Shapes ON Shapes.ID = Form.ID) 
LEFT JOIN Texts ON Texts.ID = Form.ID) 
WHERE Forms.Name = 'History'

我从一些SO用户那里读到，这种访问大量列/字段的方法是不恰当或不好的做法。在许多表都相关的情况下获取大量字段的正确方法或思路是什么？

Answer 1

您的查询中的问题是select *，而不是联接。如果Form.Id确实是您要加入的字段，那么这些联接可能很好。

而是列出select：

中的列

SELECT col1, col2, col3 . . .
FROM ((((((((((((((((Forms 
LEFT JOIN Layouts ON Layouts.Name = Forms.Name) 
LEFT JOIN Layout ON Layout.Name = Forms.Name) 
LEFT JOIN Form ON Form.Name = Forms.Name) 
LEFT JOIN Sections ON Sections.ID] = Form.ID) 
LEFT JOIN Checks ON Checks.ID = Form.ID) 
LEFT JOIN Dates ON Dates.ID = Form.ID) 
LEFT JOIN Combos ON Combos.ID = Form.ID) 
LEFT JOIN Labels ON Labels.ID = Form.ID) 
LEFT JOIN Flash ON Flash.ID = Form.ID) 
LEFT JOIN Links ON Links.ID = Form.ID) 
LEFT JOIN Groups ON Groups.ID = Form.ID) 
LEFT JOIN Lists ON Lists.ID = Form.ID) 
LEFT JOIN Pictures ON Pictures.ID = Form.ID) 
LEFT JOIN Grids ON Grids.ID = Form.ID) 
LEFT JOIN Shapes ON Shapes.ID = Form.ID) 
LEFT JOIN Texts ON Texts.ID = Form.ID) 
WHERE Forms.Name = 'History'

组合大量表和字段的正确方法是什么？

1 个答案: