Add convenience extensions to SQLJoinBuilder, SQLSelectBuilder, SQLAl…

…ias, and SQLBinaryExpression to simplify SQLKit queries in several common use cases. (#136)

Sources/SQLKit/Builders/SQLJoinBuilder.swift

@@ -60,6 +60,30 @@ extension SQLJoinBuilder {
         self.join(table, method: method, on: SQLBinaryExpression(left: left, op: op, right: right))
     }
 
+    /// Include the given table in the list of those used by the query,
+    /// performing an explicit join using the given method and condition(s).
+    /// Tables are joined left to right, in the same order as invocations of
+    /// `from()` and `join()`. The table specifier is a string assumed to be
+    /// a valid SQL identifier. The join method may be an arbitrary expression.
+    /// The condition is a triplet of inputs representing a binary expression.
+    ///
+    /// - Parameters:
+    ///   - table: The name of the table to join.
+    ///   - method: An expression providing the join method to use.
+    ///   - left: The left side of a binary expression used as a join condition.
+    ///   - op: The operator in a binary expression used as a join condition.
+    ///   - right: The right side of a binary expression used as a join condition.
+    @discardableResult
+    public func join(
+        _ table: String,
+        method: SQLExpression = SQLJoinMethod.inner,
+        on left: SQLExpression,
+        _ op: SQLBinaryOperator,
+        _ right: SQLExpression
+    ) -> Self {
+        self.join(SQLIdentifier(table), method: method, on: left, op, right)
+    }
+
     /// Include the given table in the list of those used by the query,
     /// performing an explicit join using the given method and a list of column
     /// names to be used as shorthand join conditions. Tables are joined left to

Sources/SQLKit/Builders/SQLSelectBuilder.swift

@@ -175,6 +175,23 @@ extension SQLSelectBuilder {
         return columns.reduce(self) { $0.column($1) }
     }
 
+    /// Specify a column to retrieve as a `String`, and an alias for it with another `String`.
+    @discardableResult
+    public func column(_ column: String, as alias: String) -> Self {
+        self.column(SQLIdentifier(column), as: SQLIdentifier(alias))
+    }
+
+    /// Specify a column to retrieve as an `SQLExpression`, and an alias for it with a `String`.
+    @discardableResult
+    public func column(_ column: SQLExpression, as alias: String) -> Self {
+        self.column(column, as: SQLIdentifier(alias))
+    }
+
+    /// Specify a column to retrieve as an `SQLExpression`, and an alias for it with another `SQLExpression`.
+    @discardableResult
+    public func column(_ column: SQLExpression, as alias: SQLExpression) -> Self {
+        self.column(SQLAlias(column, as: alias))
+    }
 }
 
 // MARK: From

Sources/SQLKit/Query/SQLAlias.swift

@@ -13,3 +13,9 @@ public struct SQLAlias: SQLExpression {
         self.alias.serialize(to: &serializer)
     }
 }
+
+extension SQLAlias {
+    public init(_ expression: SQLExpression, as alias: String) {
+        self.init(expression, as: SQLIdentifier(alias))
+    }
+}

Sources/SQLKit/Query/SQLBinaryExpression.swift

@@ -17,3 +17,9 @@ public struct SQLBinaryExpression: SQLExpression {
         self.right.serialize(to: &serializer)
     }
 }
+
+extension SQLBinaryExpression {
+    public init(_ left: SQLExpression, _ op: SQLBinaryOperator, _ right: SQLExpression) {
+        self.init(left: left, op: op, right: right)
+    }
+}