documenting SUM, TOTAL, AVG, COUNT

* by some insane oversight on my part, these were missing until now.
  I think perhaps I'd thought I'd caught them under "Math"

docs/print.html

@@ -590,11 +590,11 @@ <h2 id="group-by"><a class="header" href="#group-by">GROUP BY</a></h2>
 clause or a column created with an <a href="sql/functions.html#aggregate-functions">aggregate function</a>,
 such as <code>SUM</code>.</p>
 <pre><code class="language-sql">SELECT name, price FROM products GROUP BY name, price;
-SELECT name, sum(price) FROM products GROUP BY name;
+SELECT name, SUM(price) FROM products GROUP BY name;
 </code></pre>
 <h2 id="having"><a class="header" href="#having">HAVING</a></h2>
 <p><code>HAVING</code> adds a search condition to an aggregate query.</p>
-<pre><code class="language-sql">SELECT name, sum(price) FROM products GROUP BY name HAVING LENGTH(name) &gt; 4;
+<pre><code class="language-sql">SELECT name, SUM(price) FROM products GROUP BY name HAVING LENGTH(name) &gt; 4;
 </code></pre>
 <p>It is most often used with <code>GROUP BY</code> (seen above), but it is also legal
 with other aggregates:</p>
@@ -1231,6 +1231,26 @@ <h3 id="min-max"><a class="header" href="#min-max">MIN, MAX</a></h3>
 </code></pre>
 <p>NOTE: <code>MIN</code> and <code>MAX</code> also have non-aggregate equivalents, which are 2-arity.
 When used that way, they each return the minimum or maximum value of the two values provided.</p>
+<h3 id="sum"><a class="header" href="#sum">SUM</a></h3>
+<p>The <code>SUM</code> function returns the sum of all non-null values under the column given as a parameter.</p>
+<pre><code class="language-sql">SELECT SUM(price) FROM products;
+</code></pre>
+<p>If all values for the given column are <code>NULL</code>, <code>SUM</code> returns <code>NULL</code>.</p>
+<h3 id="total"><a class="header" href="#total">TOTAL</a></h3>
+<p>The <code>TOTAL</code> function is equivalent to <code>SUM</code> except that it returns <code>0.0</code> in the case where
+all input values are <code>NULL</code>.</p>
+<h3 id="avg"><a class="header" href="#avg">AVG</a></h3>
+<p>The <code>AVG</code> function takes a numerical-type-agnostic average of all values under the
+column given as a parameter.</p>
+<pre><code class="language-sql">SELECT AVG(price) FROM products;
+</code></pre>
+<h3 id="count"><a class="header" href="#count">COUNT</a></h3>
+<p>The <code>COUNT</code> function returns the count of <em>non-null</em>, <em>non-empty</em> values for the specified column.</p>
+<pre><code>SELECT COUNT(price) FROM sales;
+</code></pre>
+<p>NOTE: Because null/empty values are ignored, the behaviour of <code>COUNT</code> will differ from other
+SQL dialects. Whether or not <code>COUNT(price)</code> and <code>COUNT(1)</code> are equivalent is dependent on
+whether the <code>price</code> attribute exists with a non-null value on each document.</p>
 <h3 id="array_agg"><a class="header" href="#array_agg">ARRAY_AGG</a></h3>
 <p>The <code>ARRAY_AGG</code> function concatenates the results of an expression into an array.
 The parameter may be <a href="sql/queries.html#order-by-sorting-results">ordered</a>

docs/sql/functions.html

@@ -369,6 +369,26 @@ <h3 id="min-max"><a class="header" href="#min-max">MIN, MAX</a></h3>
 </code></pre>
 <p>NOTE: <code>MIN</code> and <code>MAX</code> also have non-aggregate equivalents, which are 2-arity.
 When used that way, they each return the minimum or maximum value of the two values provided.</p>
+<h3 id="sum"><a class="header" href="#sum">SUM</a></h3>
+<p>The <code>SUM</code> function returns the sum of all non-null values under the column given as a parameter.</p>
+<pre><code class="language-sql">SELECT SUM(price) FROM products;
+</code></pre>
+<p>If all values for the given column are <code>NULL</code>, <code>SUM</code> returns <code>NULL</code>.</p>
+<h3 id="total"><a class="header" href="#total">TOTAL</a></h3>
+<p>The <code>TOTAL</code> function is equivalent to <code>SUM</code> except that it returns <code>0.0</code> in the case where
+all input values are <code>NULL</code>.</p>
+<h3 id="avg"><a class="header" href="#avg">AVG</a></h3>
+<p>The <code>AVG</code> function takes a numerical-type-agnostic average of all values under the
+column given as a parameter.</p>
+<pre><code class="language-sql">SELECT AVG(price) FROM products;
+</code></pre>
+<h3 id="count"><a class="header" href="#count">COUNT</a></h3>
+<p>The <code>COUNT</code> function returns the count of <em>non-null</em>, <em>non-empty</em> values for the specified column.</p>
+<pre><code>SELECT COUNT(price) FROM sales;
+</code></pre>
+<p>NOTE: Because null/empty values are ignored, the behaviour of <code>COUNT</code> will differ from other
+SQL dialects. Whether or not <code>COUNT(price)</code> and <code>COUNT(1)</code> are equivalent is dependent on
+whether the <code>price</code> attribute exists with a non-null value on each document.</p>
 <h3 id="array_agg"><a class="header" href="#array_agg">ARRAY_AGG</a></h3>
 <p>The <code>ARRAY_AGG</code> function concatenates the results of an expression into an array.
 The parameter may be <a href="queries.html#order-by-sorting-results">ordered</a>

docs/sql/queries.html

@@ -296,11 +296,11 @@ <h2 id="group-by"><a class="header" href="#group-by">GROUP BY</a></h2>
 clause or a column created with an <a href="functions.html#aggregate-functions">aggregate function</a>,
 such as <code>SUM</code>.</p>
 <pre><code class="language-sql">SELECT name, price FROM products GROUP BY name, price;
-SELECT name, sum(price) FROM products GROUP BY name;
+SELECT name, SUM(price) FROM products GROUP BY name;
 </code></pre>
 <h2 id="having"><a class="header" href="#having">HAVING</a></h2>
 <p><code>HAVING</code> adds a search condition to an aggregate query.</p>
-<pre><code class="language-sql">SELECT name, sum(price) FROM products GROUP BY name HAVING LENGTH(name) &gt; 4;
+<pre><code class="language-sql">SELECT name, SUM(price) FROM products GROUP BY name HAVING LENGTH(name) &gt; 4;
 </code></pre>
 <p>It is most often used with <code>GROUP BY</code> (seen above), but it is also legal
 with other aggregates:</p>

src/sql/functions.md

@@ -301,6 +301,42 @@ SELECT MAX(price) FROM products;
 NOTE: `MIN` and `MAX` also have non-aggregate equivalents, which are 2-arity.
 When used that way, they each return the minimum or maximum value of the two values provided.
 
+### SUM
+
+The `SUM` function returns the sum of all non-null values under the column given as a parameter.
+
+```sql
+SELECT SUM(price) FROM products;
+```
+
+If all values for the given column are `NULL`, `SUM` returns `NULL`.
+
+### TOTAL
+
+The `TOTAL` function is equivalent to `SUM` except that it returns `0.0` in the case where
+all input values are `NULL`.
+
+### AVG
+
+The `AVG` function takes a numerical-type-agnostic average of all values under the
+column given as a parameter.
+
+```sql
+SELECT AVG(price) FROM products;
+```
+
+### COUNT
+
+The `COUNT` function returns the count of _non-null_, _non-empty_ values for the specified column.
+
+```
+SELECT COUNT(price) FROM sales;
+```
+
+NOTE: Because null/empty values are ignored, the behaviour of `COUNT` will differ from other
+SQL dialects. Whether or not `COUNT(price)` and `COUNT(1)` are equivalent is dependent on
+whether the `price` attribute exists with a non-null value on each document.
+
 ### ARRAY_AGG
 
 The `ARRAY_AGG` function concatenates the results of an expression into an array.

src/sql/queries.md

@@ -207,15 +207,15 @@ such as `SUM`.
 
 ```sql
 SELECT name, price FROM products GROUP BY name, price;
-SELECT name, sum(price) FROM products GROUP BY name;
+SELECT name, SUM(price) FROM products GROUP BY name;
 ```
 
 ## HAVING
 
 `HAVING` adds a search condition to an aggregate query.
 
 ```sql
-SELECT name, sum(price) FROM products GROUP BY name HAVING LENGTH(name) > 4;
+SELECT name, SUM(price) FROM products GROUP BY name HAVING LENGTH(name) > 4;
 ```
 
 It is most often used with `GROUP BY` (seen above), but it is also legal