TSQL Where Statement OR + AND - tsql

Question

I have a very basic SELECT statement that is causing me some grief.
I have a primary table of tools that I am selecting data from. In that table, I only want tools where the status is not Decommissioned.
From there, I am checking the tool name against my LIKE clause to see if it's a close match. This is done for my AJAX typeahead.
Lastly, it's joining a table called akas which contains tool names that can also be used in reference to the main tool. These are basically other aliases the tools go by.
The issue I am facing is that it is still including records with the Decommissioned status. I am pretty sure its the WHERE clause.. Any thoughts?
SELECT t.toolName,
t.tool AS toolID,
t.toolType,
t.toolStatus,
e1.PreferredName AS ownerFirst,
e1.LastName AS ownerLast,
e1.NTID AS ownerNTID
FROM dbo.ti_tools AS t
LEFT OUTER JOIN
dbo.ti_toolAKAs AS a
ON t.tool = a.tool
LEFT OUTER JOIN dbo.EmployeeTable AS e1
ON t.toolOwner = e1.QID
WHERE (t.toolName LIKE '%' + #tool + '%') OR (a.aka LIKE '%' + #tool + '%')
AND t.toolStatus <> 'Decommissioned'
ORDER BY t.toolName ASC
FOR XML PATH ('tools'), TYPE, ELEMENTS, ROOT ('root');

Answer 1

Order of operations
AND has greater precedence than OR.
Change your WHERE clause to the following, using parentheses around the two OR conditions to separate them logically from the commission check:
WHERE ((t.toolName LIKE '%' + #tool + '%') OR (a.aka LIKE '%' + #tool + '%'))
AND t.toolStatus <> 'Decommissioned'
Your original WHERE clause was being evaluated identically to this:
WHERE (t.toolName LIKE '%' + #tool + '%') OR
((a.aka LIKE '%' + #tool + '%') AND t.toolStatus <> 'Decommissioned')

Answer 2

Add round brackets:
SELECT t.toolName,
t.tool AS toolID,
t.toolType,
t.toolStatus,
e1.PreferredName AS ownerFirst,
e1.LastName AS ownerLast,
e1.NTID AS ownerNTID
FROM dbo.ti_tools AS t
LEFT OUTER JOIN dbo.ti_toolAKAs AS a
ON t.tool = a.tool
LEFT OUTER JOIN dbo.EmployeeTable AS e1
ON t.toolOwner = e1.QID
WHERE ((t.toolName LIKE '%' + #tool + '%') OR (a.aka LIKE '%' + #tool + '%'))
AND t.toolStatus <> 'Decommissioned'
ORDER BY t.toolName ASC
FOR XML PATH ('tools'), TYPE, ELEMENTS, ROOT ('root');
The case is very simple:
cond1 OR cond2 AND cond3
<=>
cond1 OR (cond2 AND cond3)
And you get records that satisfy only cond1. What you really want is:
(cond1 OR cond2) AND cond3