动态创建的sql不开心

Question

I have a table which contains records of a 'widget' many of the columns contain just the Id of a record in a different table. When editing the widget record users are allowed to do a save even if it is incomplete. They can open it later and continue. The problem I have, is when it is incomplete my query returns nothing because the where clause contain fields which have default 0 in them and there is no match in the other tables. Here is a sample of script which illustrates this problem.

select Client,Make,Model,Shape
from
widget,clients,makes,models,shapes
where 
widget.ClientId = '3' and
widget.MakeId = makes.Id and
widget.ModelId = models.Id and
widget.ShapeId = shapes.Id 

I am building this query dynamically using PHP so am trying to keep it as simple as possible. All sugestions welcome, thanks.

Answer 1

The problem is that you are using an implicit inner join (implicit meaning that you do the join in the where clause). Inner joins return matching records only, therefore if some of the data are incomplete, no records will be returned.

Use an outer join instead, that return all records from one of the tables in the join and the matching records from the other table (MySQL does not support full outer join, but this is not relevant here anyway).

Based on your description widget table is your main table, so use left join to join all other tables on widget to get the widget even if it is incomplete:

select c.Client, m.make, md.model, s.shape
from widget w
left join clients c on c.id = w.ClientId
left join makes m on m.id = w.MakeId
left join models md on md.id = w.ModelId
left join shapes s on s.id = w.ShapeId

Answer 2

select c.Client, m.make, md.model, s.shape
from widget w
join clients c on c.id = w.ClientId
join makes m on m.id = w.MakeId
join models md on md.id = w.ModelId
join shapes s on s.id = w.ShapeId

Use Joins instead of multiple tables in FROM Clause.

Answer 3

Instead of direct join use LEFT JOIN so that no matter if there is records from other tables, still first table entries will be returned:

SELECT Client, Make, Model, Shape
FROM widget
LEFT JOIN clients ON widget.ClientId = widget.Id
LEFT JOIN makes ON widget.MakeId = makes.Id
LEFT JOIN models ON widget.ModelId = models.Id
LEFT JOIN shapes ON widget.ShapeId = shapes.Id
WHERE widget.ClientId = 3

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Table columns should be in lower case

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Table names should be in singular form, eg model , shape

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Foreign keys should be in other table. Instead of widget having ModelId , model should have widget id

I may be wrong if relations are different