Question

我有这个查询，如果表格中不存在相同ID的金额等于或高于此金额，则应插入金额。

我在MySQL 5.1和MSSQL 2k5下试过这个：

的MySQL

INSERT IGNORE INTO test（id，amount） SELECT 6,50 FROM测试什么不存在（选择1来自测试WHERE数量＆gt; = 50 AND id = 6）LIMIT 1

MSSQL

INSERT INTO test（id，amount） SELECT 6,50 FROM测试什么不存在（选择TOP 1 1 FROM测试WHERE数量＆gt; = 50 AND id = 6）

如果表中至少有一个条目，则此查询可以正常工作。如果表是空的，它将永远不会工作。这与MySQL（5.1）和MSSQL（2005）下的行为相同。我不明白为什么。即使表格完全为空，任何人都有解释和修复此查询的方法吗？

编辑：我主要需要MySQL;

更新：我专门为MySQL启动了一个新问题： MySQL Problem with inserting a row with certain conditions

Answer 1

它失败，因为select语句根据返回的行数选择值6和50。由于您的表是空的 - 没有返回任何行来获得这些值。

将其修改为

 INSERT INTO test (id, amount) SELECT 6, 50 WHERE NOT EXISTS (SELECT TOP 1 1 FROM test WHERE amount >= 50 AND id = 6)

Answer 2

按如下方式更改您的查询：

INSERT INTO test (id, amount) 
SELECT 6, 50 FROM test 
WHERE (SELECT count(*) FROM test WHERE amount >= 50 AND id = 6) = 0

Answer 3

我一步一步地尝试了这个：

    -- create a test-table with one entry
SELECT id = 1, amount = 50 
into #TEST

-- see if statement works when table is not empty
INSERT INTO #test (id, amount)  
SELECT id = 6, amount = 50 
FROM #test  
WHERE NOT EXISTS (SELECT * FROM #test WHERE amount >= 50 AND id = 6) 

-- show content of test-table
select * from #test

-- empty the test table
truncate table #test

-- try to insert a first dataentry
INSERT INTO #test (id, amount)  
SELECT id = 6, amount = 50 
FROM #test  
WHERE NOT EXISTS (SELECT * FROM #test WHERE amount >= 50 AND id = 6) 
union
SELECT id = 6, amount = 50 
where (SELECT C = COUNT(*)  FROM #test WHERE amount >= 50 AND id = 6) = 0

-- show content of test-table
select * from #test

-- remove Test-table
drop table #test

首先我尝试重现这种行为，是的，这很奇怪。工会 - 想想管理空表案件，并且这很好。

Answer 4

好吧，那是真正的问题。试试这个，使用第二个表（＃test2）：

    -- create a test-table with one entry
SELECT id = 1, amount = 50 
into #TEST

-- create a second test-table with one entry
SELECT id = 1, amount = 50 
into #TEST2

-- see if statement works when table is not empty
INSERT INTO #test (id, amount)  
SELECT id = 6, amount = 50 
FROM #test  
WHERE NOT EXISTS (SELECT * FROM #test WHERE amount >= 50 AND id = 6) 

-- show content of test-table
select * from #test

-- empty the test table
truncate table #test

INSERT INTO #test (id, amount) SELECT 6, 50 WHERE NOT EXISTS (SELECT TOP 1 1 FROM #test WHERE amount >= 50 AND id = 6)  

-- try to insert a first dataentry
INSERT INTO #test (id, amount)  
SELECT id = 6, amount = 50 
FROM #test  
WHERE NOT EXISTS (SELECT * FROM #test WHERE amount >= 50 AND id = 6) 
union
SELECT id = 6, amount = 50 
from #test2
where (SELECT C = COUNT(*)  FROM #test) = 0


-- show content of test-table
select * from #test

-- remove Test-table
drop table #test

（假设您知道前面带有＃的表，这是MS-SQL中的临时表。）

BonyT已经解释了原因。

INSERT和WHERE NOT EXISTS的奇怪SQL行为

4 个答案: