sp_BlitzIndex: prefix ambiguous columns in check_id 21

Fixes BrentOzarULTD#3957

Check 21 (More Than 5 Percent NC Indexes Are Unused) joins #IndexSanity
to an aggregated derived table aliased `perc`, and `perc` exposes its own
`database_name`. The outer SELECT and WHERE referenced several columns
without a table alias, including `database_name`, which SQL Server rejected
with "Ambiguous column name 'database_name'" at @mode = 4.

Prefix every column in the check 21 outer query and its inner derived
table with the correct alias (i., sz., or perc.) so the query parses
cleanly and future joins don't reintroduce the ambiguity.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: BrentOzar

sp_BlitzIndex.sql

@@ -5197,50 +5197,51 @@ BEGIN
             RAISERROR(N'check_id 21: More Than 5 Percent NC Indexes Are Unused', 0,1) WITH NOWAIT;
             INSERT    #BlitzIndexResults ( check_id, index_sanity_id, Priority, findings_group, finding, [database_name], URL, details, index_definition,
                                             secret_columns, index_usage_summary, index_size_summary )
-                        SELECT  21 AS check_id, 
-                                MAX(i.index_sanity_id) AS index_sanity_id, 
+                        SELECT  21 AS check_id,
+                                MAX(i.index_sanity_id) AS index_sanity_id,
                                 150 AS Priority,
                                 N'Over-Indexing' AS findings_group,
                                 N'More Than 5 Percent NC Indexes Are Unused' AS finding,
-                                [database_name] AS [Database Name],
+                                i.[database_name] AS [Database Name],
                                 N'https://www.brentozar.com/go/IndexHoarder' AS URL,
                                 CAST (MAX(perc.percent_NC_indexes_unused) AS NVARCHAR(30)) + N' percent NC indexes (' + CAST(COUNT(*) AS NVARCHAR(10)) + N') unused. ' +
                                 N'These take up ' + CAST (MAX(perc.NC_indexes_unused_reserved_MB) AS NVARCHAR(30)) + N'MB of space.' AS details,
                                 i.database_name + ' (' + CAST (COUNT(*) AS NVARCHAR(30)) + N' indexes)' AS index_definition,
-                                '' AS secret_columns, 
-                                CAST(SUM(total_reads) AS NVARCHAR(256)) + N' reads (ALL); '
-                                    + CAST(SUM([user_updates]) AS NVARCHAR(256)) + N' writes (ALL)' AS index_usage_summary,
-                                
-                                REPLACE(CONVERT(NVARCHAR(30),CAST(MAX([total_rows]) AS MONEY), 1), '.00', '') + N' rows (MAX)'
-                                    + CASE WHEN SUM(total_reserved_MB) > 1024 THEN 
-                                        N'; ' + CAST(CAST(SUM(total_reserved_MB)/1024. AS NUMERIC(29,1)) AS NVARCHAR(30)) + 'GB (ALL)'
-                                    WHEN SUM(total_reserved_MB) > 0 THEN
-                                        N'; ' + CAST(CAST(SUM(total_reserved_MB) AS NUMERIC(29,1)) AS NVARCHAR(30)) + 'MB (ALL)'
+                                '' AS secret_columns,
+                                CAST(SUM(i.total_reads) AS NVARCHAR(256)) + N' reads (ALL); '
+                                    + CAST(SUM(i.[user_updates]) AS NVARCHAR(256)) + N' writes (ALL)' AS index_usage_summary,
+
+                                REPLACE(CONVERT(NVARCHAR(30),CAST(MAX(sz.[total_rows]) AS MONEY), 1), '.00', '') + N' rows (MAX)'
+                                    + CASE WHEN SUM(sz.total_reserved_MB) > 1024 THEN
+                                        N'; ' + CAST(CAST(SUM(sz.total_reserved_MB)/1024. AS NUMERIC(29,1)) AS NVARCHAR(30)) + 'GB (ALL)'
+                                    WHEN SUM(sz.total_reserved_MB) > 0 THEN
+                                        N'; ' + CAST(CAST(SUM(sz.total_reserved_MB) AS NUMERIC(29,1)) AS NVARCHAR(30)) + 'MB (ALL)'
                                     ELSE ''
                                     END AS index_size_summary
                         FROM    #IndexSanity i
                         JOIN    #IndexSanitySize sz ON i.index_sanity_id = sz.index_sanity_id
                         JOIN (
                                 SELECT  i.database_name,
-                                        CAST((100.00 * SUM(CASE WHEN total_reads = 0 THEN 1 ELSE 0 END)) / COUNT(*) AS NUMERIC(29,1)) AS percent_NC_indexes_unused,
-                                        CAST(SUM(CASE WHEN total_reads = 0 THEN sz.total_reserved_MB ELSE 0 END) AS NUMERIC(29,1)) AS NC_indexes_unused_reserved_MB
+                                        CAST((100.00 * SUM(CASE WHEN i.total_reads = 0 THEN 1 ELSE 0 END)) / COUNT(*) AS NUMERIC(29,1)) AS percent_NC_indexes_unused,
+                                        CAST(SUM(CASE WHEN i.total_reads = 0 THEN sz.total_reserved_MB ELSE 0 END) AS NUMERIC(29,1)) AS NC_indexes_unused_reserved_MB
                                 FROM    #IndexSanity i
                                 JOIN    #IndexSanitySize sz ON i.index_sanity_id = sz.index_sanity_id
-                                WHERE   index_id NOT IN ( 0, 1 )
+                                WHERE   i.index_id NOT IN ( 0, 1 )
                                         AND i.is_unique = 0
                                         /*Skipping tables created in the last week, or modified in past 2 days*/
                                         AND i.create_date < DATEADD(dd,-7,GETDATE())
                                         AND i.modify_date < DATEADD(dd,-2,GETDATE())
                                 GROUP BY i.database_name
                              ) AS perc ON i.database_name = perc.database_name
-                        WHERE    index_id NOT IN ( 0, 1 )
+                        WHERE    i.index_id NOT IN ( 0, 1 )
                                 AND i.is_unique = 0
-                                AND total_reads = 0
+                                AND i.total_reads = 0
                                 /*Skipping tables created in the last week, or modified in past 2 days*/
                                 AND	i.create_date < DATEADD(dd,-7,GETDATE())
                                 AND i.modify_date < DATEADD(dd,-2,GETDATE())
                                 AND perc.percent_NC_indexes_unused >= 5
-                        GROUP BY i.database_name 
+                                AND sz.total_reserved_MB >= CASE WHEN (@GetAllDatabases = 1 OR @Mode = 0) THEN @ThresholdMB ELSE sz.total_reserved_MB END
+                        GROUP BY i.database_name
                 OPTION    ( RECOMPILE );
 
             RAISERROR(N'check_id 23: Indexes with 7 or more columns. (Borderline)', 0,1) WITH NOWAIT;