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Comment:Additional clarification on syntax restrictions in SELECT statements.
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SHA1:4c5d78209a5b03a04c805cca2db21d50bcf265e3
User & Date: drh 2014-01-30 15:32:07
Context
2014-01-30
15:56
Update the mmap documentation to describe the problem of Windows not truncating memory mapped files. check-in: fa77748670 user: drh tags: trunk
15:32
Additional clarification on syntax restrictions in SELECT statements. check-in: 4c5d78209a user: drh tags: trunk
15:03
Further enhancements to the SELECT documentation. check-in: 979599b0b6 user: drh tags: trunk
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<p>The "[select-stmt]" syntax diagram above attempts to show as much of the
SELECT statement syntax as possible in a single diagram, as some readers
find that helpful.  Alternative syntax diagrams that break the syntax down
into smaller chunks are shown elsewhere in this document.

<p>Note that there are paths through the syntax diagrams for SELECT that
are not allowed in practice.  For example, an [ORDER BY] or [LIMIT] clause


can only occur on the right-most SELECT of a [compound select], even though
the [select-stmt] syntax diagram shows that they can occur anywhere. 
And, a [VALUES] clause may not immediately follow a [WITH] clause in
a [simple SELECT] even though the [extended-simple-select-stmt] diagram
shows that it can.  Restrictions such as these are described in the text.






<p>The SELECT statement is the most complicated command in the SQL language.
To make the description easier to follow, some of the passages below describe
the way the data returned by a SELECT statement is determined as a series of
steps. It is important to keep in mind that this is purely illustrative -
in practice neither SQLite nor any other SQL engine is required to follow 
this or any other specific process.
................................................................................
</ul>


<h3>The WITH Clause</h3>

<p>SELECT statements may be optional preceded by a single
[WITH clause] that defines one or more [common table expressions]
for using within the SELECT statement.



<tcl>
##############################################################################
Section UPDATE update {UPDATE *UPDATEs}

RecursiveBubbleDiagram update-stmt
</tcl>







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any changes to the database.

<p>The "[select-stmt]" syntax diagram above attempts to show as much of the
SELECT statement syntax as possible in a single diagram, as some readers
find that helpful.  Alternative syntax diagrams that break the syntax down
into smaller chunks are shown elsewhere in this document.

<p>Note that there are paths through the syntax diagrams that
are not allowed in practice.  Some example:
<ul>
<li>An [ORDER BY] or [LIMIT] clause can only occur on the right-most 
    SELECT of a [compound select].


<li>A [VALUES] clause can be the first element in a [compound SELECT]
    that uses a [WITH] clause, but a [simple SELECT] that consists of
    just a [VALUES] clause cannot be preceded by a [WITH] clause.
<li>The [WITH] clause must occur on the first SELECT of a [compound SELECT].
    It cannot follow a [compound-operator].
</ul>
These and other similar syntax restrictions are described in the text.

<p>The SELECT statement is the most complicated command in the SQL language.
To make the description easier to follow, some of the passages below describe
the way the data returned by a SELECT statement is determined as a series of
steps. It is important to keep in mind that this is purely illustrative -
in practice neither SQLite nor any other SQL engine is required to follow 
this or any other specific process.
................................................................................
</ul>


<h3>The WITH Clause</h3>

<p>SELECT statements may be optional preceded by a single
[WITH clause] that defines one or more [common table expressions]
for use within the SELECT statement.  Contrary to what the
[select-stmt] syntax diagram shows, a [WITH clause] cannot occur
after a [compound-operator].

<tcl>
##############################################################################
Section UPDATE update {UPDATE *UPDATEs}

RecursiveBubbleDiagram update-stmt
</tcl>