Loop in MySql, or alternative?

问题

I have a MySql db with innoDB tables. Very simplified this is how two tables are layed out:

Table A:

• controlID(PK)
• controlText

Table B:

• controlOptionID(pk)
• controlID(FK to table A)
• controlOptionType
• controlOptionValue

So many controlOptions(table B) can reference one control(giving that control multiple options). But for each option two rows are made in table B: one row with controlOptionType = "linkToCreator" and controlOptionValue = (an ID to the template it was made from*). And the other row type = "optionSelected" and value = "true"(or false).

• = its a pretty complicated setup, but basically instead of set columns we are making dynamic ones by means of the type being what the column would have been called. So I couldnt link to the template with FK.

So now I need to select every control(which will have 2 controlOptions linking to it) where the one controlOptionValue value is true or false(depending on what i need) and the other controlOptionValue is an text ID that I specify.

What I think is the best way to do it is a

SELECT * FROM tableB WHERE controlOptionType = 'linkToCreator'

Then do a loop over that result set saying:

SELECT * FROM tableB WHERE tableB.controlID = (the controlID in this iterations row) AND tableB.controlValue = 'true'

But maybe thatls really inefficient, and either way I have no clue how to do that. It would be great if I could get a single query(i.e. not using stored procedures) that I specified templateID and true or false and it gave me a row result if it didn't find anything.

BTW this is for a search in our application with will need to go through TONS of rows so performance is paramount. And yes, I know the setup isnt the greatest...

Thanks :D

回答1:

Like this?

SELECT * FROM tableA AS A
LEFT JOIN tableB AS ctrl1 ON (A.controlID = ctrl1.controlID AND ctrl1.controlOptionType = ? AND ctrl1.controlOptionValue = ?)
LEFT JOIN tableB AS ctrl2 ON (A.controlID = ctrl2.controlID AND ctrl2.controlOptionType = ? AND ctrl2.controlOptionValue = ?)

回答2:

Try this:

SELECT * 
FROM Table_A 
LEFT JOIN Table_B
ON Table_A.ControlID = Table_B.ControlID
WHERE Table_A.controlOptionType = 'linkToCreator

来源：https://stackoverflow.com/questions/3339477/loop-in-mysql-or-alternative