Question

Need some help with a SQL query.

I have three tables TestOptions, CreateScript and TestResults.

Testoptions holds all data for a particular test. CreateScript holds collections of tests which are run in order, denoted by index. TestResults hold the results.

I want to display a list of tests for a particular instrument. The list will contain. TestType, TestName, limits of the test and the result. Some tests may not have been carried out yet so the there will be no entry for that test in the test results table. If there the test has not been carried out, the test details still need to be retrieved. The list will be ordered by index and grouped by TestType.

So far I’ve got:

SELECT TestType, TestName, LowerLimits, UpperLimits, ResultRecorded  
FROM CreateScriptTable 
INNER JOIN TestOptionsTable ON CreateScriptTable.TestName =T estOptionsTable.TestName 
LEFT JOIN TestResultsTable ON CreateScriptTable.TestName = TestResultsTable.TestName 
WHERE CreateScriptTable.InstrumentType= 'instType' 
AND jobNo ='000'
AND SerialNo ='000'
ORDER BY [Index] ASC, TestType

SerialNo and JobNo are only in TestResults table.
This query only gives the details of the tests that have been entered in the test results table. I would like all test details and the result if the test has been completed.

The expected output is as follows:

TestType    TestName    Lower       Upper       Result
type1       test1       12            20        12
type1       test2       96           108        105
type2       test2       98           108        
type3       test3       95           105

The actual output is more like

TestType    TestName    Lower       Upper       Result
type1       test1       12            20        12
type1       test2       96            108       105

Only tests with entries in the results table showing.

Possibly I am not approaching the joins correctly. I have messed around with inner, left, right and full joins but to no avail and am pretty stumped right now.

Answer 1

You can move your criteria for columns in the left-joined table from the WHERE clause to the JOIN clause to prevent them from virtually changing your left join to an inner join like so:

SELECT TestType, TestName, LowerLimits, UpperLimits, ResultRecorded  
FROM CreateScriptTable 
INNER JOIN TestOptionsTable ON CreateScriptTable.TestName =TestOptionsTable.TestName 
LEFT JOIN TestResultsTable ON CreateScriptTable.TestName = TestResultsTable.TestName AND jobNo ='000' AND SerialNo ='000'
WHERE CreateScriptTable.InstrumentType= 'instType' 
ORDER BY [Index] ASC, TestType