How do update to table1.column value from table2.rows count with where condition in SQL server

Question

如何使用SQL Server中的where条件从table2.rows更新到table1.column值

Answer 1

Give this a go. See if it gives you enough to work with.

DECLARE @TABLE1 AS TABLE (KeyField CHAR(1)
                         ,CountField INT
                         )
DECLARE @TABLE2 AS TABLE (KeyField CHAR(1)
                         ,OtherData NVARCHAR(MAX)
                         )

INSERT  INTO @TABLE1
        (KeyField, CountField)
VALUES  ('A', 0) 
,       ('B', 0)
,       ('C', 0)

INSERT  INTO @TABLE2
        (KeyField, OtherData)
VALUES  ('A', CAST(NEWID() AS NVARCHAR(MAX)))
,       ('A', CAST(NEWID() AS NVARCHAR(MAX)))
,       ('B', CAST(NEWID() AS NVARCHAR(MAX)))
,       ('B', CAST(NEWID() AS NVARCHAR(MAX)))
,       ('B', CAST(NEWID() AS NVARCHAR(MAX)))
,       ('C', CAST(NEWID() AS NVARCHAR(MAX)))

;
WITH    cte
          AS (SELECT    KeyField
              ,         COUNT(1) AS Cnt
              FROM      @TABLE2
              GROUP BY  KeyField
             )
    UPDATE  T1
    SET     T1.CountField = T2.Cnt
    FROM    @TABLE1 T1
    JOIN    cte T2 ON T2.KeyField = T1.KeyField

SELECT * FROM @TABLE1

For future ref it helps if you can post some data sets and expected results. For now though this should get you going in the right direction.