MySQL 将来自两个单独且复杂的查询的列合并为一行

Question

I'm working on a website where there are many distinct lines of garments. A line is defined as garments of the same design, style, manufacturer etc. Within a line, garments come in different sizes and colours.

To compose a chart of all the colours available in one particular line the following query works fine (I'm working in Coldfusion but PHP would use the same query).

SELECT 
skuColourwayID,cHex,cLongName,skuID, cwColID1
from garment_sku
join garment_colourways
on cwID=skuColourwayID
join garment_colour_name
on cID=cwColID1
where skuLineID= <cfqueryPARAM value = "#url.lnID#" CFSQLType = "CF_SQL_INTEGER">
group by skuColourwayID

In order to accumulate all the info I need, I have to access three tables using joins. (I don't have any choice about how the data is presented to me). The line is identified by lnID which in the above case starts as a url variable. Starting with the sku table (garment_sku) I access the colourways table (garment_colourways) and get the colourway colour id (cwColID1). By applying this to the colour name table (garment_colour_name) I can get the actual name of the colour, and it's hex value.

This all works perfectly, EXCEPT a few garments come in bi-colours (ie different colour sleeves to body or collar etc). There is a second column in the garment_sku table, cwColID2 which denotes the second colour.

One way around this would be to perform two separate queries, where cwColID1 is replaced by cwColID2 in the second query. I could then combine the queries programatically to achive the bi-colour where required. However, this seems rather inelegant and I'm sure MySQL has a way of dealing with this in one query?

I hate to say it but there is also provison in the tables for a third colourway cwColID3 though I've never come across any three colour garments and would be very happy to solve this for just the two colours.

Thanks for any help you can give.

Answer 1

You just need to JOIN to the garment_colour_name table a second time to get the name of the second colour. Note that since not all garments will have 2 colours, you need to use a LEFT JOIN rather than an INNER JOIN :

SELECT 
    skuColourwayID,
    gc1.cHex AS c1Hex, 
    gc1.cLongName AS c1Name,
    gc2.cHex AS c2Hex,
    gc2.cLongName AS c2Name,
    skuID, 
    cwColID1,
    cwColID2
from garment_sku
join garment_colourways
on cwID=skuColourwayID
join garment_colour_name gc1
on gc1.cID=cwColID1
left join garment_colour_name gc2
on gc2.cID=cwColID2
where skuLineID= <cfqueryPARAM value = "#url.lnID#" CFSQLType = "CF_SQL_INTEGER">
group by skuColourwayID