Differences between equal sign(=) and IN with subquery

问题

I have a query it takes 20 seconds to execute, follow my query:

SELECT MATLIGA.COD_MAT_FAMILIA 
FROM 
    ORCAMENTOS.dbo.OR_1INSUMOS INSUMOS
    INNER JOIN ORCAMENTOS.dbo.OR_MAT_GRUPOS GRUPOS ON (GRUPOS.EMPRESA='01' AND GRUPOS.FILIAL='01' AND GRUPOS.CODIGO_INTERNO = 'HOT' )
    INNER JOIN ORCAMENTOS.dbo.OR_MATERIAIS MATER ON (MATER.EMPRESA='01' AND MATER.FILIAL='01' AND MATER.CODIGO_GRUPO=GRUPOS.ID AND MATER.ID = INSUMOS.COD_INSUMO_MATER )
    INNER JOIN ORCAMENTOS.dbo.OR_MAT_LIGACAO MATLIGA ON (MATLIGA.EMPRESA='01' AND MATLIGA.FILIAL='01' AND MATLIGA.CODIGO_MATERIAL  = INSUMOS.COD_INSUMO_MATER)
WHERE INSUMOS.EMPRESA='01' AND INSUMOS.FILIAL='01' 
AND INSUMOS.COD_INSUMO_MATER IS NOT NULL 
AND INSUMOS.NUMERO=10865812 
AND INSUMOS.OPCAO_SIMULACAO=1 
AND INSUMOS.CODIGO_MAQUINA = (SELECT COD_MAQ_PROPOSTA FROM ORCAMENTOS.dbo.OR_1SIMULACOES AS ORC WHERE  ORC.NUMERO=10865812 AND ORC.OPCAO_SIMULACAO = 1 AND ORC.EMPRESA='01' AND ORC.FILIAL='01' )  
AND INSUMOS.OPCAO_MAQUINA = (SELECT OPCAO_MAQUINA FROM ORCAMENTOS.dbo.OR_1SIMULACOES AS ORC WHERE  ORC.NUMERO=10865812 AND ORC.OPCAO_SIMULACAO = 1  AND ORC.EMPRESA='01' AND ORC.FILIAL='01' )  
GROUP BY MATLIGA.COD_MAT_FAMILIA  
ORDER BY  1 

In these two lines bellow, if I change the equal signal by (IN), ( = ALL ) or ( = ANY ) it reduces the costs to 1 second.

AND INSUMOS.CODIGO_MAQUINA IN (SELECT COD_MAQ_PROPOSTA FROM ORCAMENTOS.dbo.OR_1SIMULACOES AS ORC WHERE  ORC.NUMERO=10865812 AND ORC.OPCAO_SIMULACAO = 1 AND ORC.EMPRESA='01' AND ORC.FILIAL='01' )  
AND INSUMOS.OPCAO_MAQUINA IN (SELECT OPCAO_MAQUINA FROM ORCAMENTOS.dbo.OR_1SIMULACOES AS ORC WHERE  ORC.NUMERO=10865812 AND ORC.OPCAO_SIMULACAO = 1  AND ORC.EMPRESA='01' AND ORC.FILIAL='01' )  

Whats the difference between them?

Tks.

回答1:

There is a small semantic difference. The first query must fail if the subquery matches more than one record. So it has to finish the subquery until the end:

where col1 = (select col1 from table2)

The second query can stop once it encounters a match:

where col1 in (select col1 from table2)

来源：https://stackoverflow.com/questions/13741582/differences-between-equal-sign-and-in-with-subquery