Question

我有两个选择查询

如果查询1有结果，则返回该结果
如果查询1未产生结果，则执行查询2

这两个查询来自同一个表，但查询条件不能共存。

我该怎么做？

Answer 1

您可以尝试使用@@ ROWCOUNT ...

IF OBJECT_ID('tempdb..#TestData', 'U') IS NOT NULL 
DROP TABLE #TestData;

CREATE TABLE #TestData (
    SomeNumber INT NOT NULL 
    );
INSERT #TestData (SomeNumber) VALUES (1), (2), (3), (4), (5);

--=====================================================

SELECT * FROM #TestData td WHERE td.SomeNumber = 22;

IF @@ROWCOUNT = 0
BEGIN 
    SELECT * FROM #TestData td WHERE td.SomeNumber <= 5;
END;

Answer 2

使用IF ELSE

的另一种方法

IF ((SELECT COUNT(1) FROM table_name WHERE condition_1 ) = 0) 
    SELECT col_1, col_2, ... col_n FROM table_name WHERE condition_2
ELSE 
    SELECT col_1, col_2, ... col_n FROM table_name WHERE condition_1

Answer 3

这将检查query1是否有结果并将其设置为变量。如果ELSE将检查是否有query1的结果，那么query1否则query2

DECLARE @rec_cnt INT

SET @rec_cnt = (SELECT 1
                  FROM table
                 WHERE condition1)

IF @rec_cnt IS NOT NULL 
   (SELECT *
      FROM table
     WHERE condition1);
ELSE
   (SELECT *
      FROM table
     WHERE condition2);

Answer 4

IF EXISTS (SELECT TOP 1 1 FROM table1 WHERE condition1)
    SELECT col_1, col_2 FROM table1 WHERE condition1
ELSE 
     SELECT col_1, col_2 FROM table1 WHERE condition2

两个SQL查询语句，只选择一个

4 个答案: