diff --git a/jOOQ/src/main/java/org/jooq/Select.java b/jOOQ/src/main/java/org/jooq/Select.java
index ef4f806d1f..b7eb0368a3 100644
--- a/jOOQ/src/main/java/org/jooq/Select.java
+++ b/jOOQ/src/main/java/org/jooq/Select.java
@@ -233,7 +233,7 @@ extends
      * Subject to change in future jOOQ versions, use at your own risk.
      */
     @Experimental
-    UnmodifiableList<? extends SelectFieldOrAsterisk> $distinctOn();
+    @NotNull UnmodifiableList<? extends SelectFieldOrAsterisk> $distinctOn();
 
     /**
      * Experimental query object model accessor method, see also {@link QOM}.
diff --git a/jOOQ/src/main/java/org/jooq/conf/Settings.java b/jOOQ/src/main/java/org/jooq/conf/Settings.java
index 5e12c165da..2d48c537db 100644
--- a/jOOQ/src/main/java/org/jooq/conf/Settings.java
+++ b/jOOQ/src/main/java/org/jooq/conf/Settings.java
@@ -177,6 +177,8 @@ public class Settings
     @XmlElement(defaultValue = "true")
     protected Boolean transformPatternsCaseElseNull = true;
     @XmlElement(defaultValue = "true")
+    protected Boolean transformPatternsCaseElseCase = true;
+    @XmlElement(defaultValue = "true")
     protected Boolean transformPatternsTrivialCaseAbbreviation = true;
     @XmlElement(defaultValue = "true")
     protected Boolean transformPatternsTrivialPredicates = true;
@@ -2139,6 +2141,34 @@ public class Settings
         this.transformPatternsCaseElseNull = value;
     }
 
+    /**
+     * Transform <code>CASE … ELSE CASE …</code> by flattening the nested <code>CASE</code>.
+     * <p>
+     * <code>CASE WHEN a THEN b ELSE CASE WHEN c THEN d END END</code> is equivalent to <code>CASE WHEN a THEN b WHEN c THEN d END</code>.
+     * <p>
+     * This feature is available in the commercial distribution only.
+     * 
+     * @return
+     *     possible object is
+     *     {@link Boolean }
+     *     
+     */
+    public Boolean isTransformPatternsCaseElseCase() {
+        return transformPatternsCaseElseCase;
+    }
+
+    /**
+     * Sets the value of the transformPatternsCaseElseCase property.
+     * 
+     * @param value
+     *     allowed object is
+     *     {@link Boolean }
+     *     
+     */
+    public void setTransformPatternsCaseElseCase(Boolean value) {
+        this.transformPatternsCaseElseCase = value;
+    }
+
     /**
      * Transform trivial case abbreviations like <code>NVL(NULL, a)</code> to <code>a</code>.
      * <p>
@@ -5161,6 +5191,11 @@ public class Settings
         return this;
     }
 
+    public Settings withTransformPatternsCaseElseCase(Boolean value) {
+        setTransformPatternsCaseElseCase(value);
+        return this;
+    }
+
     public Settings withTransformPatternsTrivialCaseAbbreviation(Boolean value) {
         setTransformPatternsTrivialCaseAbbreviation(value);
         return this;
@@ -6140,6 +6175,7 @@ public class Settings
         builder.append("transformPatternsMergeRangePredicates", transformPatternsMergeRangePredicates);
         builder.append("transformPatternsMergeBetweenSymmetricPredicates", transformPatternsMergeBetweenSymmetricPredicates);
         builder.append("transformPatternsCaseElseNull", transformPatternsCaseElseNull);
+        builder.append("transformPatternsCaseElseCase", transformPatternsCaseElseCase);
         builder.append("transformPatternsTrivialCaseAbbreviation", transformPatternsTrivialCaseAbbreviation);
         builder.append("transformPatternsTrivialPredicates", transformPatternsTrivialPredicates);
         builder.append("transformPatternsScalarSubqueryCountAsteriskGtZero", transformPatternsScalarSubqueryCountAsteriskGtZero);
@@ -6844,6 +6880,15 @@ public class Settings
                 return false;
             }
         }
+        if (transformPatternsCaseElseCase == null) {
+            if (other.transformPatternsCaseElseCase!= null) {
+                return false;
+            }
+        } else {
+            if (!transformPatternsCaseElseCase.equals(other.transformPatternsCaseElseCase)) {
+                return false;
+            }
+        }
         if (transformPatternsTrivialCaseAbbreviation == null) {
             if (other.transformPatternsTrivialCaseAbbreviation!= null) {
                 return false;
@@ -7958,6 +8003,7 @@ public class Settings
         result = ((prime*result)+((transformPatternsMergeRangePredicates == null)? 0 :transformPatternsMergeRangePredicates.hashCode()));
         result = ((prime*result)+((transformPatternsMergeBetweenSymmetricPredicates == null)? 0 :transformPatternsMergeBetweenSymmetricPredicates.hashCode()));
         result = ((prime*result)+((transformPatternsCaseElseNull == null)? 0 :transformPatternsCaseElseNull.hashCode()));
+        result = ((prime*result)+((transformPatternsCaseElseCase == null)? 0 :transformPatternsCaseElseCase.hashCode()));
         result = ((prime*result)+((transformPatternsTrivialCaseAbbreviation == null)? 0 :transformPatternsTrivialCaseAbbreviation.hashCode()));
         result = ((prime*result)+((transformPatternsTrivialPredicates == null)? 0 :transformPatternsTrivialPredicates.hashCode()));
         result = ((prime*result)+((transformPatternsScalarSubqueryCountAsteriskGtZero == null)? 0 :transformPatternsScalarSubqueryCountAsteriskGtZero.hashCode()));
diff --git a/jOOQ/src/main/java/org/jooq/impl/Patterns.java b/jOOQ/src/main/java/org/jooq/impl/Patterns.java
index 5e88619685..5110b2274f 100644
--- a/jOOQ/src/main/java/org/jooq/impl/Patterns.java
+++ b/jOOQ/src/main/java/org/jooq/impl/Patterns.java
@@ -1722,6 +1722,13 @@ package org.jooq.impl;
 
 
 
+
+
+
+
+
+
+
 
 
 
diff --git a/jOOQ/src/main/java/org/jooq/impl/QOM.java b/jOOQ/src/main/java/org/jooq/impl/QOM.java
index eee1a79ec8..543fb3dc4d 100644
--- a/jOOQ/src/main/java/org/jooq/impl/QOM.java
+++ b/jOOQ/src/main/java/org/jooq/impl/QOM.java
@@ -251,7 +251,13 @@ public final class QOM {
             java.util.List<Q>
         permits
             QueryPartListView
-    {}
+    {
+        @NotNull default UnmodifiableList<Q> $concat(UnmodifiableList<Q> other) {
+            QueryPartList<Q> r = new QueryPartList<>(this);
+            r.addAll(other);
+            return r;
+        }
+    }
 
     public /*sealed*/ interface With
         extends
diff --git a/jOOQ/src/main/resources/org/jooq/xsd/jooq-runtime-3.18.0.xsd b/jOOQ/src/main/resources/org/jooq/xsd/jooq-runtime-3.18.0.xsd
index db0fb86afe..c32981d557 100644
--- a/jOOQ/src/main/resources/org/jooq/xsd/jooq-runtime-3.18.0.xsd
+++ b/jOOQ/src/main/resources/org/jooq/xsd/jooq-runtime-3.18.0.xsd
@@ -560,6 +560,14 @@ This feature is available in the commercial distribution only.]]></jxb:javadoc><
 This feature is available in the commercial distribution only.]]></jxb:javadoc></jxb:property></appinfo></annotation>
       </element>
       
+      <element name="transformPatternsCaseElseCase" type="boolean" minOccurs="0" maxOccurs="1" default="true">
+        <annotation><appinfo><jxb:property><jxb:javadoc><![CDATA[Transform <code>CASE .. ELSE CASE ..</code> by flattening the nested <code>CASE</code>.
+<p>
+<code>CASE WHEN a THEN b ELSE CASE WHEN c THEN d END END</code> is equivalent to <code>CASE WHEN a THEN b WHEN c THEN d END</code>.
+<p>
+This feature is available in the commercial distribution only.]]></jxb:javadoc></jxb:property></appinfo></annotation>
+      </element>
+      
       <element name="transformPatternsTrivialCaseAbbreviation" type="boolean" minOccurs="0" maxOccurs="1" default="true">
         <annotation><appinfo><jxb:property><jxb:javadoc><![CDATA[Transform trivial case abbreviations like <code>NVL(NULL, a)</code> to <code>a</code>.
 <p>