40 lines
1.2 KiB
Plaintext
40 lines
1.2 KiB
Plaintext
== Why is this an issue?
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An "EXISTS" statement is generally used to select/update/delete some rows of a table based on the content of columns of other tables.
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If the "SELECT" statement used as argument of the "EXISTS" statement is always returning "true" for all rows of the main ``++SELECT++`` statement, the ``++EXISTS++`` statement is useless and has the same effect as if it was not there. Still, this is probably not the original intend of the developer to have an ``++EXISTS++`` statement that is always true.
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As a consequence, the ``++SELECT++`` statement of an ``++EXISTS++`` statement should always contain a ``++WHERE++`` clause.
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What is true for ``++EXISTS++`` is also true for ``++NOT EXISTS++``.
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=== Noncompliant code example
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[source,text]
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----
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SELECT *
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FROM sys.[databases] AS [sd]
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WHERE EXISTS (SELECT 1
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FROM [sys].[master_files] AS [mf])
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----
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=== Compliant solution
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[source,text]
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----
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SELECT *
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FROM sys.[databases] AS [sd]
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WHERE EXISTS (SELECT 1
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FROM [sys].[master_files] AS [mf]
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WHERE [mf].[database_id] = [sd].[database_id])
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----
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=== Exceptions
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This rule doesn't raise an issue when ``++EXISTS++`` is used in the context of a ``++WHILE++`` or a ``++IF++`` statement.
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