问题:

I have this query which works but when I try to write the equivalent in LINQ I get the incorrect SQL produced.

My query is:

SELECT COUNT(*)
FROM tableName
GROUP BY ColumnId

I've tried writing it as:

tableName.GroupBy(x => x.ColumnId).Count()

But looking in LINQPad it is producing the SQL:

SELECT COUNT(*) AS [value]
FROM (
SELECT NULL AS [EMPTY]
FROM [tableName] AS [t0]
GROUP BY [t0].[ColumnId]
) AS [t1]

What am I doing wrong? Thanks!

回答1:

Your LINQ query is counting the number of groups but your SQL query is producing the counts by group. You want

var counts = tableName.GroupBy(x => x.ColumnId)
                      .Select(g => new { g.Key, Count = g.Count() });

to get the counts by group.

Note that if you want exactly the same SQL you want

var counts = tableName.GroupBy(x => x.ColumnId)
                      .Select(g => g.Count());

The first example above should be a little more useful as it gives the ids of each group as well.

Try tableName.GroupBy(x => x.ColumnId).Select(x => x.Count())