Sql server 显示类型转换警告的执行计划-在Cond列上

正在表达式中获取类型转换。。。。。可能会影响查询范围选择中的“CardinalityEstimate”。 表T1和T2都具有聚集索引

如何克服警告

CREATE TABLE T1
(
    KEY INT IDENTITY(1,1) NOT NULL,
    CODE VARCHAR(50), 
    DESCRIPTION VARCHAR(100),
    EXTERNAL_KEY VARCHAR(15),
    FLAG BIT
) 

INSERT INTO T1 VALUES(1,'ASS','DESC','NULL',0) 
INSERT INTO T1 VALUES(1,'ASS1','DESC','45213',1) 
INSERT INTO T1 VALUES(1,'ASS2','DESC','NULL',1) 
INSERT INTO T1 VALUES(1,'ASS3','DESC','NULL',0) 
INSERT INTO T1 VALUES(1,'ASS4','DESC','56321',1)

CREATE TABLE T2
(
    KEY INT IDENTITY(1,1) NOT NULL,
    CODE VARCHAR(50), 
    DESCRIPTION VARCHAR(100),
    EXTERNAL_KEY NUMERIC(14,0)
)

INSERT INTO T2 VALUES(1,'DSA','DESC',51256) 
INSERT INTO T2 VALUES(1,'DSA1','DESC',45213) 
INSERT INTO T2 VALUES(1,'DSA2','DESC',51256) 
INSERT INTO T2 VALUES(1,'DSA3','DESC',56321)

实际查询：

SELECT T1.KEY,T1.FLAG,T2.KEY, FROM T2 INNER JOIN T1 ON 
CAST(NULLIF(RTRIM(T1.EXTERNAL_KEY),'') AS NUMERIC(14,0)) = T2.EXTERNAL_KEY
WHERE T1.EXTERNAL_KEY IS NOT NULL

---

示例数据和查询都存在一些问题

KEY INT IDENTITY（1,1）NOT NULL

应更改为

[KEY]NOT NULL

或不插入标识列

插入T1值（'ASS'、'DESC'、'NULL'，0）

当您用单引号括住'NULL'时，您也不插入DB NULL，而是插入文本NULL。为了这个。下面的代码应该可以工作

---

---

但是，我认为您希望NULL为NULL而不是文本，因此请将插入内容从插入T1（代码、描述、外部密钥、标志）值（'ASS'，'DESC'，'NULL'，0）更改为插入T1（代码、描述、外部密钥、标志）值（'ASS'，'DESC'，NULL，0）

---

样本数据 密码

SELECT T1.[KEY],T1.FLAG,T2.[KEY]
FROM T2 
INNER JOIN T1 
ON NULLIF(T1.EXTERNAL_KEY ,'NULL')=T2.EXTERNAL_KEY 
WHERE T1.EXTERNAL_KEY IS NOT NULL

IF OBJECT_ID('tempdb..#T1') IS NOT NULL
    DROP TABLE #T1

IF OBJECT_ID('tempdb..#T2') IS NOT NULL
    DROP TABLE #T2

CREATE TABLE #T1
(
    [KEY] INT IDENTITY(1,1) NOT NULL,
    CODE VARCHAR(50), 
    DESCRIPTION VARCHAR(100),
    EXTERNAL_KEY VARCHAR(15),
    FLAG BIT
) 
GO

INSERT INTO #T1(CODE,DESCRIPTION,EXTERNAL_KEY,FLAG) VALUES('ASS','DESC',NULL,0) 
INSERT INTO #T1(CODE,DESCRIPTION,EXTERNAL_KEY,FLAG) VALUES('ASS1','DESC','45213',1) 
INSERT INTO #T1(CODE,DESCRIPTION,EXTERNAL_KEY,FLAG)VALUES('ASS2','DESC',NULL,1) 
INSERT INTO #T1(CODE,DESCRIPTION,EXTERNAL_KEY,FLAG)VALUES('ASS3','DESC',NULL,0) 
INSERT INTO #T1(CODE,DESCRIPTION,EXTERNAL_KEY,FLAG)VALUES('ASS4','DESC','56321',1)

CREATE TABLE #T2
(
    [KEY] INT IDENTITY(1,1) NOT NULL,
    CODE VARCHAR(50), 
    DESCRIPTION VARCHAR(100),
    EXTERNAL_KEY NUMERIC(14,0)
)
GO

INSERT INTO #T2 (CODE,DESCRIPTION,EXTERNAL_KEY) VALUES('DSA','DESC',51256) 
INSERT INTO #T2 (CODE,DESCRIPTION,EXTERNAL_KEY)VALUES('DSA1','DESC',45213) 
INSERT INTO #T2 (CODE,DESCRIPTION,EXTERNAL_KEY)VALUES('DSA2','DESC',51256) 
INSERT INTO #T2 (CODE,DESCRIPTION,EXTERNAL_KEY)VALUES('DSA3','DESC',56321)

SELECT #T1.[KEY],#T1.FLAG,#T2.[KEY]
FROM #T2 
INNER JOIN #T1 
ON NULLIF(#T1.EXTERNAL_KEY ,NULL)=#T2.EXTERNAL_KEY 
WHERE #T1.EXTERNAL_KEY IS NOT NULL