Join operators.

src/main/java/com/alexfu/sqlitequerybuilder/builder/JoinOnBuilder.java

@@ -17,7 +17,23 @@ public SelectWhereBuilder where(String condition) {
   }
 
   public SelectJoinBuilder join(String table) {
-    return new SelectJoinBuilder(this, table);
+    return new SelectJoinBuilder(this, table, JoinType.JOIN);
+  }
+
+  public SelectJoinBuilder leftOuterJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.LEFT_OUTER_JOIN);
+  }
+
+  public SelectJoinBuilder crossJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.CROSS_JOIN);
+  }
+
+  public SelectJoinBuilder naturalJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.NATURAL_JOIN);
+  }
+
+  public SelectJoinBuilder naturalLeftOuterJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.NATURAL_LEFT_OUTER_JOIN);
   }
 
   @Override

src/main/java/com/alexfu/sqlitequerybuilder/builder/JoinType.java

@@ -0,0 +1,19 @@
+package com.alexfu.sqlitequerybuilder.builder;
+
+public enum JoinType {
+    JOIN("JOIN"),
+    CROSS_JOIN("CROSS JOIN"),
+    LEFT_OUTER_JOIN("LEFT OUTER JOIN"),
+    NATURAL_JOIN("NATURAL JOIN"),
+    NATURAL_LEFT_OUTER_JOIN("NATURAL LEFT OUTER JOIN");
+
+    private final String sql;
+
+    JoinType(String sql) {
+        this.sql = sql;
+    }
+
+    public final String toSQL() {
+        return sql;
+    }
+}

src/main/java/com/alexfu/sqlitequerybuilder/builder/SelectFromBuilder.java

@@ -17,7 +17,23 @@ public SelectWhereBuilder where(String condition) {
   }
 
   public SelectJoinBuilder join(String table) {
-    return new SelectJoinBuilder(this, table);
+    return new SelectJoinBuilder(this, table, JoinType.JOIN);
+  }
+
+  public SelectJoinBuilder leftOuterJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.LEFT_OUTER_JOIN);
+  }
+
+  public SelectJoinBuilder crossJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.CROSS_JOIN);
+  }
+
+  public SelectJoinBuilder naturalJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.NATURAL_JOIN);
+  }
+
+  public SelectJoinBuilder naturalLeftOuterJoin(String table) {
+    return new SelectJoinBuilder(this, table, JoinType.NATURAL_LEFT_OUTER_JOIN);
   }
 
   public SelectOrderByBuilder orderBy(String column) {

src/main/java/com/alexfu/sqlitequerybuilder/builder/SelectJoinBuilder.java

@@ -8,10 +8,12 @@ public class SelectJoinBuilder extends SegmentBuilder {
 
   private Builder prefix;
   private String table;
+  private JoinType joinType;
 
-  public SelectJoinBuilder(Builder prefix, String table) {
+  public SelectJoinBuilder(Builder prefix, String table, JoinType joinType) {
     this.prefix = prefix;
     this.table = table;
+    this.joinType = joinType;
   }
 
   public JoinOnBuilder on(String condition) {
@@ -20,6 +22,6 @@ public JoinOnBuilder on(String condition) {
 
   @Override
   public String build() {
-    return join(" ", prefix.build(), "JOIN", table);
+    return join(" ", prefix.build(), joinType.toSQL(), table);
   }
 }

src/test/java/com/alexfu/sqlitequerybuilder/SelectTest.java

@@ -4,6 +4,7 @@
 
 import com.alexfu.sqlitequerybuilder.api.SQLiteQueryBuilder;
 import com.alexfu.sqlitequerybuilder.api.SelectType;
+import com.alexfu.sqlitequerybuilder.builder.JoinType;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
@@ -63,6 +64,52 @@ public void selectJoinTest() {
     assertThat(query).isEqualTo( "SELECT * FROM mytable JOIN secondtable ON mytable.id = secondtable.id WHERE id = 1");
   }
 
+  @Test
+  public void selectLeftOuterJoinTest() {
+    String query = SQLiteQueryBuilder
+            .select("*")
+            .from("mytable")
+            .leftOuterJoin("secondtable")
+            .on("mytable.id = secondtable.id")
+            .where("id = 1")
+            .build();
+
+    assertThat(query).isEqualTo( "SELECT * FROM mytable LEFT OUTER JOIN secondtable ON mytable.id = secondtable.id WHERE id = 1");
+  }
+
+  @Test
+  public void selectCrossJoinTest() {
+    String query = SQLiteQueryBuilder
+            .select("*")
+            .from("mytable")
+            .crossJoin("secondtable")
+            .build();
+
+    assertThat(query).isEqualTo( "SELECT * FROM mytable CROSS JOIN secondtable");
+  }
+
+  @Test
+  public void selectNaturalJoinTest() {
+    String query = SQLiteQueryBuilder
+            .select("*")
+            .from("mytable")
+            .naturalJoin("secondtable")
+            .build();
+
+    assertThat(query).isEqualTo( "SELECT * FROM mytable NATURAL JOIN secondtable");
+  }
+
+  @Test
+  public void selectNaturalLeftOuterJoinTest() {
+    String query = SQLiteQueryBuilder
+            .select("*")
+            .from("mytable")
+            .naturalLeftOuterJoin("secondtable")
+            .build();
+
+    assertThat(query).isEqualTo( "SELECT * FROM mytable NATURAL LEFT OUTER JOIN secondtable");
+  }
+
   @Test
   public void selectMultiJoinTest() {
     String query = SQLiteQueryBuilder