使用的选择语句具有不同数量的mysql列

Question

I have an error "the used select statements have a different number of columns mysql"

My query

SELECT
* FROM
inventory 
WHERE
barcode1 = 'DR963560860GYYQBKBBD2' 
OR barcode2 = 'DR963560860GYYQBKBBD2' 
OR barcode3 = 'DR963560860GYYQBKBBD2' 
OR barcode4 = 'DR963560860GYYQBKBBD2' UNION
SELECT
p.id AS 'PartId',
m.`Name` AS 'Model',
c.`Name` AS 'Color',
pt.`Name` AS 'PartType' 
FROM
inventory i
JOIN part p ON p.Id = i.PartId
JOIN model m ON m.Id = p.ModelId
JOIN color c ON c.Id = p.ColorId
JOIN parttype pt ON pt.Id = p.PartTypeId 
WHERE
barcode1 = @barcode
OR barcode2 = @barcode
OR barcode3 = 'DR963560860GYYQBKBBD2' 
OR barcode4 = 'DR963560860GYYQBKBBD2';

What i want to get is all the data in inventory table in the first select statement, and another one is from another table.

Before, I have two queries which is

SELECT
    * 
     FROM
    inventory 
    WHERE
    barcode1 = @Barcode 
    OR barcode2 = @Barcode 
    OR barcode3 = @Barcode 
    OR barcode4 = @Barcode`

that will retrieve all the information in inventory and the other one is

SELECT
p.id AS 'PartId',
m.`Name` AS 'Model',
c.`Name` AS 'Color',
pt.`Name` AS 'PartType'
FROM
inventory i
JOIN part p ON p.Id = i.PartId
JOIN model m ON m.Id = p.ModelId
JOIN color c ON c.Id = p.ColorId
JOIN parttype pt ON pt.Id = p.PartTypeId 
WHERE
barcode1 = @Barcode
OR barcode2 = @Barcode
OR barcode3 = @Barcode
OR barcode4 = @Barcode

That will load just the four columns.

Since my output load too slow, i will combine it in one query. Is this possible? How can I do that?

I'm a beginner in MySQL.

Answer 1

The problem you have is because you use Union on two tables with different number of column. For Example if you get something in TableA:

| Id | Name | Age|
+----+------+----+
| 1  | Andy | 3  |

And another TableB

| Id | Name | Age| Gender |
+----+------+----+--------|
| 1  | Andy | 3  | Male   |

If you try to union them you will get error, as they cannot be combined (because of different number of columns).

So your problem is that your first Select *... return more columns than the second select where you select only 4 columns. The key to solve it, is to specify exact which columns you need to select so that both selects have same number of columns.

Something like this

SELECT
    p.id AS 'PartId',
    m.`Name` AS 'Model',
    c.`Name` AS 'Color',
    pt.`Name` AS 'PartType' 
FROM
    inventory i
    JOIN part p ON p.Id = i.PartId
    JOIN model m ON m.Id = p.ModelId
    JOIN color c ON c.Id = p.ColorId
    JOIN parttype pt ON pt.Id = p.PartTypeId 
WHERE
    i.barcode1 = 'DR963560860GYYQBKBBD2' 
    OR i.barcode2 = 'DR963560860GYYQBKBBD2' 
    OR i.barcode3 = 'DR963560860GYYQBKBBD2' 
    OR i.barcode4 = 'DR963560860GYYQBKBBD2' 
UNION
SELECT
    p.id AS 'PartId',
    m.`Name` AS 'Model',
    c.`Name` AS 'Color',
    pt.`Name` AS 'PartType' 
FROM
    inventory i
    JOIN part p ON p.Id = i.PartId
    JOIN model m ON m.Id = p.ModelId
    JOIN color c ON c.Id = p.ColorId
    JOIN parttype pt ON pt.Id = p.PartTypeId 
WHERE
    barcode1 = @barcode
    OR barcode2 = @barcode
    OR barcode3 = 'DR963560860GYYQBKBBD2' 
    OR barcode4 = 'DR963560860GYYQBKBBD2';

Answer 2

I don't see why you are using a union (ie a vertical merge) when a join(a horizontal merge) would seem more appropriate

SELECT i.*,   
p.id AS 'PartId',
m.`Name` AS 'Model',
c.`Name` AS 'Color',
pt.`Name` AS 'PartType'
FROM
inventory i
JOIN part p ON p.Id = i.PartId
JOIN model m ON m.Id = p.ModelId
JOIN color c ON c.Id = p.ColorId
JOIN parttype pt ON pt.Id = p.PartTypeId 
WHERE
barcode1 = @Barcode
OR barcode2 = @Barcode
OR barcode3 = @Barcode
OR barcode4 = @Barcode