Fix grammatical errors

site/_docs/adapter.md

@@ -221,7 +221,7 @@ runnable as a service), repository persistence, authorization and security.
 
 There are many other APIs that allow you to extend Calcite's capabilities.
 
-In this section, we briefly describe those APIs, to give you an idea what is
+In this section, we briefly describe those APIs, to give you an idea of what is
 possible. To fully use these APIs you will need to read other documentation
 such as the javadoc for the interfaces, and possibly seek out the tests that
 we have written for them.
@@ -236,7 +236,7 @@ They are straightforward to write (you just write a Java class and register it
 in your schema) but do not offer much flexibility in the number and type of
 arguments, resolving overloaded functions, or deriving the return type.
 
-It you want that flexibility, you probably need to write you a
+If you want that flexibility, you probably need to write a
 *user-defined operator*
 (see [<code>interface SqlOperator</code>]({{ site.apiRoot }}/org/apache/calcite/sql/SqlOperator.html)).
 
@@ -303,7 +303,7 @@ appear in more than one window. For example, 10:37 appears in both the
 
 Window functions are computed incrementally: when the clock ticks from
 10:14 to 10:15, two rows might enter the window and three rows leave.
-For this, window functions have have an extra life-cycle operation:
+For this, window functions have an extra life-cycle operation:
 
 * `remove` removes a value from an accumulator.
 
@@ -352,7 +352,7 @@ SELECT * FROM TABLE(Ramp(3, 4))
 {% endhighlight %}
 
 *User-defined table macros* use the same SQL syntax as table functions,
-but are defined differently. Rather than generating data, they generate an
+but are defined differently. Rather than generating data, they generate a
 relational expression.
 Table macros are invoked during query preparation and the relational expression
 they produce can then be optimized.

site/_docs/algebra.md

@@ -207,7 +207,7 @@ In this case, we create an EnumerableSort on top of the input RelNode.
 You can reference a field by name or ordinal.
 
 Ordinals are zero-based. Each operator guarantees the order in which its output
-fields occur. For example, `Project` returns the fields in the generated by
+fields occur. For example, `Project` returns the fields generated by
 each of the scalar expressions.
 
 The field names of an operator are guaranteed to be unique, but sometimes that

site/_docs/druid_adapter.md

@@ -179,7 +179,7 @@ Currently there are two types:
   but can be used to perform set operations as well.
 
 In the model definition, there is an array of Strings called `complexMetrics` that declares
-the alias for each complex metric defined. The alias is used in SQL, but it's real column name
+the alias for each complex metric defined. The alias is used in SQL, but its real column name
 is used when Calcite generates the JSON query for druid.
 
 # Foodmart data set

site/_docs/file_adapter.md

@@ -275,7 +275,7 @@ sqlline> select distinct deptno from depts;
 
 ## JSON files and model-free browsing
 
-Some files are describe their own schema, and for these files, we do not need a model. For example, `DEPTS.json` has an integer `DEPTNO` column and a string `NAME` column:
+Some files describe their own schema, and for these files, we do not need a model. For example, `DEPTS.json` has an integer `DEPTNO` column and a string `NAME` column:
 
 {% highlight json %}
 [